The Atheist Bible

Chapter on the Universe

The Atheist Bible / Chapter on the Universe. © Fabian M. Suchanek

Introduction

This chapter describes the current scientific view of the universe, including the Big Bang, the genesis of life, and the evolution of humans. The chapter consists of the following sections:

The Universe

The Earth

The Earth is spherical Wikicommons/Earth
We call “the Earth” the planet on which we perceive ourselves. The Earth is spherical. It takes the form of a huge ball. Evidence for this hypothesis is as follows Spherical Earth:
  1. When at sea it is possible to see high mountains or elevated lights in the distance before lower-lying ground and the mast of a boat before the hull. It is also possible to see further by climbing higher in the ship, or, when on land, on high cliffs.
  2. The sun is lower in the sky as you travel away from the tropics. For example, when traveling northward, stars such as Polaris, the north star, are higher in the sky, whereas other bright stars such as Canopus, visible in Egypt, disappear from the sky.
  3. The length of daylight varies more between summer and winter the farther you are from the equator.
  4. The Earth throws a circular shadow on the moon during a lunar eclipse.
  5. The times reported for lunar eclipses (which are seen simultaneously) are many hours later in the east (e.g. India) than in the west (e.g. Europe). Local times are confirmed later by travel using chronometers and telegraphic communication.
  6. When you travel far south, to Ethiopia or India, the sun throws a shadow south at certain times of the year. Even farther (e.g. Argentina) and the shadow is always in the south.
  7. It is possible to circumnavigate the world; that is, to travel around the world and return to where you started. Travelers who circumnavigate the Earth observe the gain or loss of a day relative to those who did not.
  8. An artificial satellite can circle the Earth continuously and even be geostationary.
  9. the Earth appears as a disc on photographs taken from space, regardless of the vantage point.
We have thus found several theories that predict a spherical Earth (7, 8, 9). We have also found that the hypothesis of the spherical Earth makes correct predictions (1-6). Hence we assume that the Earth is spherical. I have also personally verified the implications of this hypothesis by traveling around the world (see my Trip around the world).
The Church says that the Earth is flat, but I know that it is round. For I have seen the shadow of the Earth on the moon and I have more faith in the shadow than in the Church.

The Sun

We observe that there are other things in space than just Earth. We can, e.g., see the Sun and the Moon. We have the theory that if we can see something, then this something has physical existence, and hence we assume that the Sun and the Moon exist physically.

People first believed that the Sun revolves around the Earth. This theory, however predicts certain things that do not coincide with our perceptions. For example, planets change their position relative to the other planets. They seem to slow down, reverse their direction, and then accelerate again in the original direction (see picture).

Mars traces a loop in the sky Tunç Tezel

The Earth (green) overtakes Mars (red) while both turn counter-clockwise. In this process, Mars seems first right, then left, then right again, and then left. ThinkQuest
This was one of the observations that prompted Galileo Galilei to doubt the geocentric theory. A similar thing happens to the stars: A star that was first left of another star appears right to the other star a few months later. Again a few months later, it walks back to its original place. This contradicts the geocentric theory. If, however, we assume that the Earth revolves around the Sun, we can explain both phenomena. The picture on the right shows how Mars appears against the star background. Since the heliocentric theory predicts more correct perceptions than the geocentric one, we have accepted the former. This theory has made numerous true predictions in the past, among other things solar eclipses, lunar eclipses, and the shape of the moon at different times of the month. Hence, we assume it to be true.

Technically speaking, the Earth and the Sun attract each other through gravity. They revolve around each other, like two people who hold hands and dance around each other. However, Earth has a diameter of “only” 12,700 km. The Sun is 100 times larger than the Earth, and much heavier. Hence, the center of gravity lies entirely within the Sun. Thus, the Sun merely wobbles around this center, while the Earth follows a much larger circumference. It is more like a parent dancing with a child. Io9: the Earth revolves around the Sun — prove it

Elizabeth Anscombe: I can understand why people thought that the Sun revolves around the Earth.
Ludwig Wittgenstein: Why?
Elizabeth Anscombe: Well, it looks that way.
Ludwig Wittgenstein: How would it look if the Earth revolved around the Sun?

The Spinning Earth

The Earth revolves around the Sun with one turn per year. It also spins around its own axis, with one turn per day.
We have come to the conclusion that the Earth revolves around its own axis. This is why we have day and night: When our part of the Earth faces the Sun, we have daylight. When we turn away from the Sun, we enter into the night. The axis of the Earth is slightly tilted with respect to the axis of the movement around the Sun. In summer, our hemisphere is tilted towards the Sun. Hence, we spent longer in the illuminated half of the ball, and our days are longer. In Winter, our hemisphere is tilted away, and we spend more time during night. At the poles, the story is different: In June, the northern pole is entirely in the illuminated part of the ball, and hence the Sun never sets. The southern pole is in long darkness. In December, it is vice versa.

In summer, our hemisphere is tilted towards the Sun. Hence, the Sun rays arrive almost vertically. This is why the Sun appears high in the sky in summer. Also, we receive much more energy per square meter — it is warm. In winter, our hemisphere is tilted away from the Sun. The Sun appears low in the sky, and we receive less energy per square meter, because the surface is at an angle to the Sun rays — it is cold. At the Equator, the effects are minimal, because the Sun rays arrive nearly vertically throughout the year. Hence, there are no seasons. Thus, this theory offers not just true predictions, but also a surprising compression of different natural phenomena.

You might wonder why we do not feel the spinning of the Earth. This is because the atmosphere moves with us. When you are in an airplane and you close your eyes, you do not feel that you are moving at 1000 km per hour. You do not even feel when the plane flies in a curve. The same is true for our journey on Earth. There is one way to feel the spin, though: At the equator the centrifugal force is larger than at the poles. Hence, we are just a tiny bit more heavy at the poles. Since gravity remains the dominant force, this change is small: You gain 0.3% of your weight. But it is still measurable.

The Sun, with all the planets revolving around it, can still rapen a bunch of grapes — as if it had nothing else in the Universe to do.
Galileo Galilei (ascribed)

The Universe

The location of Earth in the Universe Wikicommons/Earth’s location in the universe
There are not just the Earth and the Sun in the Universe. There are other planets and stars. These objects emit or reflect light that we can see. We can even estimate their distance to our planet. This works as follows: We measure the angle at which the star is visible in December. Then we measure the angle again in June. Since the Earth has traveled around the Sun in these 6 months, the angles are slightly different. From these two angles and the distance of the Earth to the Sun, we can compute the distance of the star. This technique works for stars that are rather “close” (300 light years away).

For the other stars, we proceed as follows: Astronomers are able to spread out the white light into its constituent “rainbow” of colors. This is called the stellar spectrum. With the stars within the 300 light year range, astronomers have shown that stars with similar spectra have similar intensity of brightness. This allows them to predict the distance of stars beyond the 300 light year range. The spectra of the star is photographed and compared with the spectra of nearby stars whose distance is known. This will tell the actual brightness of the star. Measuring the apparent brightness (the farther it is, the less bright it will seem) the astronomer can then determine the distance of the star needed to give it that level of brightness. This method can be used for stars up to tens of thousands of light years away from the Earth. Rejection of Pascal’s wager / Age of the universe.

In recent times, more technology has become available: We can emit radio waves, and measure how they are reflected by celestial bodies. We can launch satellites and have them send back data. We can even send people to space and have them take pictures.

These techniques have led to the following conclusions: the Earth orbits the Sun at a distance of 150 million kilometers. The light needs 8 minutes to reach us from the Sun. We know that there are more planets orbiting the Sun than just Earth. The farthest objects orbiting the Sun are around 50 times farther from the Sun than Earth. To reach these objects, the light from the Sun needs around 7 hours (Kuiper belt; Pluto lives there). The Sun’s field of gravity reaches much farther though. The Sun’s gravity gives way to that of surrounding stars around 2 light years away from the Sun. This area makes up the Solar System.

The Solar System is just one of many such systems. Each system revolves around a star. The Solar System and its neighboring systems span a few hundred light years. This neighborhood is embedded in the Milky Way — our galaxy. The Milky Way spans 100,000 light years. This means that even if we travel at the speed of light, we would need half the time that humans exist to cross it. The Milky Way has between 200 and 400 billion stars like our Sun. So there are roughly 50 stars for every person on Earth.

The Milky Way lives in the “Local Group”. This group is not so local after all. It spans 10 million light years. The group lives in the Virgo Cluster, which spans 100 million light years. With its neighbors, the Virgo Cluster spans some billion light years. Since the Earth is roughly 5 billion years old, this means that the light that reaches us from there was sent before the Earth existed. Together with many such neighborhoods, it makes up the observable universe. It is around 100 billion light years across. This means that if a star at the fringes of the observable universe dies, it would take 50 billion years for us to notice that the light is gone. This means that the universe that we see is the universe that existed billions of years ago. According to the current scientific opinion, we cannot know how the universe is now, because no information can travel faster than light.

The Earth is at the center of the observable universe because what we can observe is 50 billion light years around us in all directions. This does not mean that the Earth would be at the center of the entire universe, of course. We do not know how big the universe is beyond what we can observe Earth’s location in the universe.

The discovery that we are just one particular species on one particular planet in one particular galaxy in our universe is making me much more humble than any burning bush ever could.
Christopher Hitchens, paraphrased from a television debate on 2010-11-26

The Big Bang

The Doppler effect
We all know the Doppler effect: When a firefighter car passes, the pitch is higher when the car approaches, and lower when the car has passed. This is because sound is a wave. When a sound-emitting body moves towards us, the waves arrive in a compressed form, which makes them sound higher. When the body moves away from us, the waves are dilated and the sound appears lower.

The same observation can be made for light. Light can be understood as waves. When these waves are delated, they do not turn “low-pitch” (as sound waves), but they turn slightly more red. Since light travels extremely fast, these effects are only visible when the light-emitting body moves away from us at an extremely high speed. We know roughly what should be the color of stars, because we know which color the nuclear reactions in them produce to emit the light. Now here is the surprise: All stars are slightly more red than they should be. This means that they are all moving away from us — at the speed of billions of kilometers per hour. This holds no matter where we look in the universe. Everything is moving away from us!

Does this mean that we are the center of the universe? Not necessarily. When you draw dots on a balloon and you inflate it, all points will move away from each other, and yet no dot is in the center any more than the others. This means that the universe is continuously expanding at incredible speeds. Ever since Edwin Hubble and his colleagues made this observation, the hypothesis of the expanding universe has been confirmed by a large number of other arguments. Among others, these are a cosmic background radiation, and predictions from Albert Einstein’s relativity theory.

Now, if the universe is expanding, this means that if we go back in time, the universe was smaller. If we go back really far, then the universe has most likely been a single dot. If this is true, then this single dot must have been very dense. This theory is commonly known as the “Big Bang theory”. Based on how fast the stars move away from us, the “big bang” must have been roughly 14 billion years ago.

Scientists have since been investigating the conditions of matter at the time after the big bang, and they have come up with theories to explain the composition of quarks, electrons, atoms, and molecules. These theories are continuously being developed, confirmed, rejected, and adjusted, as is usual in science. We can replicate the conditions near the beginning of the expansion in large particle accelerators. These studies confirm that the hypothesis of the big bang can explain today’s composition and proportion of matter in the universe. Therefore, the theory of the Big Bang is currently accepted as the best theory we have about the birth of the universe — although this may change if more evidence comes to light.

Space is big. Really big. You just won’t believe how mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space...
Douglas Adams in “A Hitchhiker’s Guide to the Galaxy”

Before the Big Bang

We have seen that the universe most likely started by a sort of Big Bang. The crucial question is, of course: What was before the big bang? Unfortunately, we do not have an answer to this question. Several theories have been proposed, including an oscillating universe, parallel universes, or a halt of time.

A halt of time is not completely illogical. To see this, consider Albert Einstein’s relativity theory. As everything in science, this theory is a set of rules. This theory predicts that time runs slower in a field of large gravity. For example, time runs slower in the center of Earth than in the sky. Absurd as this theory may sound, it has always made true predictions: Time runs indeed slightly slower close to the Earth than far away from it. The GPS satellites are a living proof. Their clocks are continuously adjusted in order to be in sync with the clocks on Earth. This is because their time runs differently from time on Earth. Now if the single dot of mass really existed at the beginning of the Big Bang, its mass must have been extremely large. This could have entailed that time did just not move at all. Then the question of “before” would not make any sense.

Still, this leaves open the question of “why” the Big Bang happened. The problem with science is that it can only propose theories that produce verifiable predictions. As long as no such theory has been found, science keeps searching. Until then, the answer to the question of why the Big Bang happened remains unknown.

Birth of the Earth

The current scientific hypothesis is that the Big Bang produced a large amount of interstellar dust and gas called the solar nebula. Gravity, inertia, and centrifugal forces formed the nebula into a rotating cloud. Gravity pulled the center of the cloud together to form a ball: The Sun was born. The compression heated the center, and this caused the start of nuclear fusion. This is a process in which two hydrogen atoms are forced so close together that their nuclei meet. The nuclei resist being forced together because they are all charged positively. If they do meet, they fuse together to a helium nucleus. This releases a large amount of energy in the form of heat. Such a fusion can be repeated in the laboratory, as Mark Oliphant showed in 1932. This is the same principle that hydrogen bombs use. The Sun fuses 620m tons of hydrogen each second. History of the Earth

How the early Earth might have looked Arguing with Atheists
The rest of the nebula was still rotating around the Sun. Again, gravity pulled together parts of the cloud, and clumped them together to form planets — a process called accretion. This process formed the Earth and the other planets. Much like for the Sun, the accretion heated up the center of the ball. However, the Earth attracted much less debris, was smaller, and hence did not start nuclear fusion. Still, the Earth was very hot. It was so hot that the metals in the debris melted, and fell to the center of the Earth. The outer layer cooled down and formed a crust. This process gave the Earth its layered structure: The inner core of the Earth is solid. It consists primarily of an iron-nickel alloy and is approximately 5000 °C hot. Its size is roughly 70% of the moon Inner core. The inner core is wrapped in the outer core, a liquid mix of iron and nickel with a temperature of about 4000 °C. The outer core is not under enough pressure to be solid. The outer layers of the Earth are cooler, and hence again solid.

At the time of the formation of the Earth, volcanism was rampant, and heat and materials from the inside of the Earth were spit out to the surface. These included water vapor. As the planet cooled, this vapor turned to water and formed the oceans. The crust of the Earth consisted of tectonic plates, and these moved around, floating on the liquid layers below. The plates moved several times before forming the continents that we know today.

The Age of the Earth

Cross section of a Sequoia Tree Web Exhibits
After having discussed the birth of planet Earth, we now turn to its age. Naturally, Earth has to be younger than the universe, i.e., younger than 14 billion years. Based on biblical sources, people have estimated the age of Earth to be around 6000 years. Biblical sources also tell us that the stars were created after the Earth (on the fourth day, see Bible/Genesis 1:14-1:19). Now here is the problem: Given that some of the stars are billions of light years away, and that we can see them, they must be billions of years old. Since the Bible tells us that the Earth is older than the stars, the Bible tells us that the Earth is billions of years old. At the same time, the Bible tells us that it is 6000 years old. Hence, the Bible contradicts itself.

Ancient trees tell us a lot about the age of the Earth. A tree adds one ring to its trunk every year. If we count the rings in a tree cross section, we can know when the tree was born. Some trees are thousands of years old. For example, we have found Bristlecone Pines aged over 5000 years Bristlecone Pine. But the rings also tell us more: In a year with good climate conditions, rings are thicker than in years with bad climate conditions. Thus, the thickness of rings gives us a pattern. Trees in the same geographic region experience the same climate conditions. Thus, all trees in the region exhibit the same pattern of ring thickness. Now let’s say we find a tree that died this year and that is 4000 years old. In its first 100 years, it exhibits a particular pattern of ring thickness. Let’s assume that we find another tree that died long ago, and that exhibits the very same pattern of ring thickness. However, this pattern now appears on the outer rings, closer to the death of the tree. Then we assume that the death of this tree coincides with the first 100 years of the first tree. Thus, we can calculate backwards when the second tree was born. We have found trees that were born 8000 years ago. Thus, the Earth must have existed 8000 years ago.

In the meantime, scientists have developed much more sophisticated methods of dating objects. The most common is so-called radiometric dating: Many atoms are unstable and will spontaneously decay into other kinds of atoms. While the moment of decay of each individual atom is completely random, in a large sample the rate of decay has been shown to be constant. The rate of decay of the radioactive atoms is specific to that particular element. This decay is normally given in terms of half-life, which is the time it takes for half the original amount of atoms (the “parent” atom) to decay to another type of atom (the “daughter” atom). The decay rate of the various particles had been determined experimentally. Thus by comparing the relative amount of “parent” and “daughter” atoms in a rock sample, a geologist can determine the age of that particular sample. There are many naturally occurring radioactive elements, with known “half-lives”, in the Earth. These can be used, when found together, to cross check the dating given by each other. One example of a radioactive element which is used for the dating of rocks is the element Potassium-40. Potassium-40 decays to Argon-40 with a half-life of 1.25 billion years. By using these radioactive clocks the oldest rock yet found in the Earth (from western Greenland) is dated at 3.9 billion years. Some moon rock samples, brought back to earth by the astronauts have been dated at 4.5 billion years. Analysis of these and other geologic and astronomical evidence led scientists to conclude that the solar system was formed about 4.6 billion years ago. Thus, the scientific estimate of the age of the Earth is larger than the one given by the Bible by a factor of a million. Rejection of Pascal’ Wager / The Creation Myths Radiometric dating

Young earth creationism is essentially the position that all of modern science, 90% of living scientists and 98% of living biologists, all major university biology departments, every major science journal, the international academy of sciences, and every major science organisation of the world, are all wrong regarding the originals and development of life.... but one particular tribe of uneducated, bronze aged, goat herders got it exactly right.
Chuck Easttom

Life

Life

One of the characteristics that distinguishes our planet from the others we know is that there is life. Different from inanimate entities, living beings can grow, reproduce, and exchange substances with the environment. This applies both to complex life forms (such as mammals and humans) and to more simple ones (such as bacteria, algae, or fungi).

According to the current scientific consensus, life started relatively early on Earth, but evolved relatively slowly. Life started “already” a few hundred million years after the birth of the Earth. Just for comparison: The time it took for life to start is 1000 times longer than the time that humanity exists. Some of the earliest forms of life that we can still see are fossils of some microorganisms on a sandstone discovered in Western Australia. These are 3.5 billion years old. These organisms consisted of only a few cells Abiogenesis. These evolved into multicellular organisms, into algae, then into plants, fish, land animals, and finally into humans.

We will now trace this process step by step.

Chemical Reactions

All matter is made of atoms. For the formation and the composition of atoms, the reader is referred to Wikipedia/Atom. Atoms can be plugged together, and the resulting structure is called a molecule. For example, two hydrogen atoms (abbreviated by “H”) attract each other by their electrical charge. Hence, they plug together and form a molecule of two hydrogens. We denote this process by
H    H    →    H-H
The left-hand side of this equation says that we have two separate hydrogen atoms. The right-hand side says that we still have two hydrogen atoms, but that these plugged together to form a molecule. This molecule is sometimes abbreviated as “H2”, because it consists of 2 hydrogen atoms.

The chemical reaction that forms water
Such molecules can again plug together to form larger molecules. They can also split up to atoms, or get transformed into other molecules. For example, water is formed when one oxygen-pair combines with two hydrogen pairs into two water molecules, as shown on the right.

In general, any process that transforms molecules or atoms into other molecules or atoms is called a chemical reaction Chemical Reaction. The chemical reaction may require heat or energy in order to proceed. In the example of water, the process requires energy to split the oxygen pairs and the hydrogen pairs. However, a chemical reaction may also emit energy. Reactions can also require the presence of other molecules (so-called catalyzers or reagents) to proceed Catalysis.

For this book, a chemical reaction is a theory that says that if certain chemical substances are brought together, and if energy and reagents or catalyzers are present as required, then a new chemical substance will form. These theories have validated themselves zillions of times. In large parts, they are testable, i.e., they can be reproduced in the laboratory. Chemical reactions also happen in real life all around us (for example, when wood burns, when soap cleans out stains, or when we cook meals).

A physicist is an atom’s way of studying itself.
Niels Bohr

Molecules

The Miller Urey Experiment Adrian J. Hunter @ Wikipedia
We have seen that atoms can plug together to form molecules. The current theory goes that when the Earth was born, volcanic eruptions released large amounts of carbon dioxide (CO2), nitrogen (N2), hydrogen sulfide (H2S), and sulfur dioxide (SO2) into the atmosphere. Lightening released heat energy, and hence there were many chemical reactions all around. Molecules just got plugged together randomly by chemical reactions from atoms and from previously assembled molecules. Some molecules would immediately dissolve thereafter, others would chemically react with other molecules, and again others would stay.

This theory can be experimentally verified, as Stanley Miller and Harold Urey showed in 1953. For this purpose, they simulated the early atmosphere of Earth by a gas mixture of methane (Ch3), ammonia (Nh2), and hydrogen (H2). They simulated the water vapor from the early oceans by pumping steam into this mixture. The steam was then allowed to condense back to water, the water was heated again to steam, pumped into the gas, and so on. Within a day, the mixture had turned pink. Miller and Urey showed that over 20 different forms of molecules had formed, many of which are basic components of living beings. Later analyses of the original experimental material showed that even more molecules had formed than those reported by Urey and Miller. Today, we know that the circumstances of the early Earth were probably different from what Urey and Miller assumed. If this experiment is repeated with gas mixtures that resemble more what we think was the original atmosphere of the Earth, then even more diverse molecules can be produced.

The Miller Urey experiment gives us a testable theory: Whenever a certain gas mixture is exposed to lightening, certain molecules form. This means that, if the early Earth had this gas mixture plus lightening, then the very same molecules formed. Interestingly, such molecules have since also been found on a comet The Guardian: Rosetta mission lander detects organic molecules on surface of comet, 2014-11-18.

Proteins

An Amino Acid
The Milley Urey Experiment produced a variety of molecules. Among these were also amino acids. Amino acids are molecules that consist of one amine (-NH2) and one carboxylic acid (-COOH), along with a side‐chain of atoms that is specific to each amino acid. The figure on the right shows the generic form of an amino acid, where the side‐chain is abbreviated by “R”:

These molecules can plug together to form peptides Peptide. This works through a chemical reaction that creates a bond between the carboxyl group of one amino acid and the amino group of another, as shown here:

Connecting two amino acids to a (small) peptide V8rik @ Wikicommons

Longer peptides are called proteins. Both peptides and proteins can perform a number of functions, if put together with other peptides, proteins, or molecules. For example, they can attach to each other through chemical bonds, alter their composition upon reacting with another molecule, decompose into smaller pieces, or aggregate to even larger molecules. All of this happens through chemical reactions. We will see a few of these in the sequel.

RNA

The Milley Urey Experiment produced a variety of larger molecules. Some of these molecules were amino acids, which can give rise to proteins. Later variants of the experiment could produce even more molecules. In particular, later experiments were able to produce nucleobases (also called nitrogenous bases). These are molecules that make up our DNA. There are 5 nucleous bases, called adenine (A), guanine (G), thymine (T), cytosine (C), and uracil (U). Two of them are shown here:

Each of these nucleobases can connect by chemical reactions to a five-carbon sugar and to a phosphate group. This yields a molecule called a nucleotide. The nucleotides for adenine and cytosine are shown here:

Two nucleotides can connect together by chemical bonds. This chemical reaction releases water, as shown here:

An RNA Molecule
Other nucleotides can bind to the free ends of this connection, so that we obtain a chain of nucleotides. Such a chain is called a Ribonucleic acid molecule (RNA). Often, the nucleotides are denoted by their initial letters, so that an RNA molecule could be, e.g., GGGAUUGUUCAA. In reality, the backbone of an RNA molecule is not straight. Bases at different points on the chain attract each other, so that the RNA forms loops (shown on the right). This gives RNA molecules a complex 3-dimensional structure.

RNA chains can be assembled in the laboratory. This gives us a theory, which basically says that if nucleotides are brought together, they form an RNA chain. This theory is testable, and has indeed been validated in the laboratory.

Chance

We have seen that certain molecules can plug together to form RNA chains — the precursor of DNA. However, only certain RNA sequences have biological functions. The others are just random sequences. Now the question is how likely it is that one particular RNA sequence got assembled by chance on the early Earth.

There are several such calculations on the Web (e.g., Ian Musgrave: Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations, 1998, The Truth About Abiogenesis And Probability, or the Fermi Paradox), but I could not find one that I would find convincing. Many of the variables in the game are just unknown. Hence, I cannot give a precise calculation here either. I can just show how such calculations usually proceed, and which factors are usually taken into account. For this purpose, I am using rather arbitrary quantities.

So here we go. Let’s say that we want to grow one particular RNA sequence, which contains 50 bases (50 is a reasonable number for an RNA sequence, but in the end it is an arbitrary choice). We start with one base. At each point of time, a new base attaches. There are 4 different bases. However, there are also other, competing molecules that can attach to our sequence, thus spoiling the entire thing. Let’s say that in total there are 10 types of molecules that can attach to our chain, and only one of them is the right one (again, 10 is an arbitrary guess). Then this gives us a chance of 1 in 10^50 of assembling that RNA sequence. This a huge number. It is roughly the total number of atoms on Earth. So is a chance of 1 in 10^50 too small to be ever met?

Several factors come into play here. First, there would not only by one RNA sequence growing, but billions of them in parallel. For comparison, one liter of water contains 10^25 molecules of water. Today’s oceans have a volume of roughly 10^21 litres of water. This means we had (and have) 10^46 molecules of water available on Earth. Assume that we have 1 base molecule per million water molecules (this is again an arbitrary guess, based on references in Ian Musgrave: Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations, 1998). Then this gives us 10^40 chains that could start in parallel. So we have a chance of 1 in 10^10 that one of them is the one we’re looking for. 10^10 is still a huge number. However, we also have a large amount of time: If it takes a day to grow such a chain (which is again an arbitrary guess), then it takes 27 million years to grow the chain we want. In comparison: Life started roughly 500 million years after the formation of the Earth.

Several additional factors come into play: Chains may be destroyed while they grow. Conditions may change during these millions of years, making it harder or easier to assemble the chains. For example, clay can speed up the formation of RNA molecules significantly Discover Magazine: What Came Before DNA?, 2014-06. The charged clay surface attracts the nucleotides and the increased local concentration of nucleotides leads to more chemical reactions Exploring Origins.org / Nucleic Acids. Another factor is that additional molecules may form over time, and these can hamper or speed up the process. Furthermore, there may be several RNA molecules that are different from the one we want to assemble, but which have the same functions. Then it is sufficient to assemble any of them. Note also that the experiment was not constrained to Earth. There are 10^22 stars in the visible universe alone. If only 1 in a million has an Earth-like planet (which is again an arbitrary guess), then this gives us 10^16 places in the universe to assemble RNA chains.

These calculations do not prove anything, because they are based on arbitrary numbers. They serve just to illustrate the magnitudes of the values involved. They also serve to illustrate that new data points may actually make the chances of life much bigger than we thought (take the example of clay). Some time ago, people thought that the chances of life were much smaller (see here for a “historical” perspective from 1996).

Be that as it may, we do know that we can build chains of amino acids to form peptides. Experiments in the laboratory show that we can build chains of 55 amino acids in 1-2 weeks Ian Musgrave: Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations, 1998. This gives us a testable theory for amino acids. It is assumed that RNA assembled in a very similar way. Experiments show that RNA chains of up to 50 nucleotides can indeed be assembled Protocell.

Replication

How RNA replication might work according to A. R. Hernández and J. A. Piccirilli: Chemical origins of life, Prebiotic RNA unstuck. Nature Chemistry, 2013
We have seen that RNA molecules can assemble by chance. It is assumed that some of these RNA molecules have the ability to replicate themselves. The figure on the right shows how this could work.

Thus, there could be RNA chains that were able to reproduce themselves. This is just one hypothesis. There are several laboratories in the world that work on self-replicating RNA chains, but as of now, none has succeeded in creating an RNA molecule that can replicate itself from individual nucleobases. As of 2016, the state of the art is:

Cells

A liposome SuperManu @ Wikipedia
So far, we have discussed how RNA molecules form. It is assumed that some of them are able to replicate. Now let us see how the first cells formed. A cell is basically a bubble‐shaped membrane, which separates the inside from the outside (shown on the right). It usually consists of molecules whose head is hydrophile, i.e., it is chemically attracted to water. Its tail is hydrophobe, i.e., it is chemically pushed away from water. When large quantities of such molecules are poured into water, they spontaneously form bubbles, because this is one of the ways in which all heads face the water and all tails are protected from water. Such a structure is called a vesicle, or liposome Liposome.

There are several molecules that have this property, and they are called lipids Lipid. One particular subclass of lipids are fatty acids. These are molecules that have a rather long tail. As other lipids, they spontaneously form vesicles when poured into water. When combined with clay (or, more precisely, montmorillonite), the process occurs even more quickly. Some of the vesicles form around the clay molecules. Since RNA attaches to the clay molecules, it is sufficient to mix fatty acids, clay, and RNA in order to get RNA chains inside vesicles. This means that we have cells that contain RNA chains Discover Magazine: What Came Before DNA?, 2004-06. The theory is that these constellations would have formed the first protocells Protocell.

Cell walls are relatively stable in their shape, but their individual fatty acids move around a lot. They enter the wall, leave the wall, or flip around from the inside to the outside and vice versa. This entails that the cell walls are permeable to certain molecules. Depending on the size, some peptides are able to walk through the cell wall. This gives us a structure that protects the RNA from larger molecules and from physical impact, and that allows other molecules to float in and out.

Cell Division

We have seen that vesicles (the ancestors of cells) are basically balls of fatty acids. Due to chemical reactions, such vesicles form spontaneously when fatty acids are in contact with water, and this process can be replicated in the laboratory. Clay plays a special role in this process, as it accelerates both the formation of vesicles and the formation of RNA. On the early Earth, storms, water movements, heat turbulences, and volcano eruptions would have mixed the elements, so that some RNA strains ended up in vesicles. Such a vesicle is called a cell. This process, likewise, can be replicated in the laboratory. The cell walls are permeable to certain molecules, and so nucleotides can enter and exit the cell. Some RNA strains are able to replicate themselves. They wait until the right molecule floats into the cell, and add it to the copy of themselves that they are currently assembling. When the copy is ready, it splits off.

Cell division.
In red: vesicles.
In blue: RNA strains.
At the same time, other vesicles would be floating around in the water. The cell ball continues to attract these vesicles, and integrate them into its cell body. Experiments in the laboratory show that vesicles grow continuously when they come in contact with other vesicles or “single” fatty acids. When cells grow, their surface increases, but their volume does not (as shown in the figure on the right). This gives the cell a prolonged shape, and makes it unstable. Eventually, it will break apart into two pieces. Now remember that we had an RNA strain and its copy floating around in the cell. If the two RNA strains happen to be in the same part of the splitting cell, then they will continue sharing that cell. However, if the cell keeps splitting, then the strains will eventually end up in two different cells. We have witnessed a cell replication and division.

At this point of the evolution, the life cycle of a cell is governed mainly by random fluctuation and random chemical reactions. Only a small fraction of the cells would actually be functional. Large numbers of cells would be empty, handicapped, mutilated, or destroyed by other chemical or physical interactions. It is possible that the entire cell population was destroyed at some point of time, and then re-formed through the same processes.

Mutation

We have seen that cells can form and replicate. The cells contain RNA strains, and these can interact with the cell wall and with other molecules or peptides in several ways. For example, we can imagine that a certain RNA strain has a subsequence of nucleotides that binds to fatty acids. Then this RNA strain would attach to the cell wall. When this RNA strain replicates, all of its copies would also attach to the cell wall.

We can also imagine that an RNA strain has a sequence that binds to certain peptides. When such peptides float into the cell, the RNA strain would accumulate them. Certain types of peptides can bind to other types of peptides, so that one particular RNA strain can end up accumulating ternary molecules in its cell. Certain peptides can interact with the wall of the cell, and either fortify it or disrupt it. If the RNA strain attracts such peptides, then the cell will behave very differently from other cells. Whenever the RNA strain replicates, it will copy this behavior to its clones.

Now we might wonder how such different behaviors come about when there was initially just one type of RNA strains that was able to replicate. The answer is that the copy mechanism of RNAs does not work 100% correctly. When one RNA assembles another RNA, it may occasionally introduce additional nucleotides or leave out others. Thus, each copy is usually slightly different from the others.

This process is called mutation. A mutation can completely destroy the behavior of the RNA. For example, if the mutation fails to maintain the subsequence that attaches to the cell wall, then the copy will lose this behavior. The mutation can also destroy the self-replication ability of the RNA. Then this particular copy will not continue to replicate. However, the mutation can also introduce new behaviors — simply because new subsequences may appear.

Early Life

At this point of our discussion, we have seen how molecules form, how peptides form, how RNA strains form, how cells form, and how cells divide and mutate. All of these processes happen purely by chemical reactions. Many of these processes can be replicated in the laboratory, giving us testable theories about them.

We have now arrived at little cells that replicate themselves, and we may discuss whether to call this “life”. Whether you want to call this “life” or not depends on how you prefer to use this word. However, the organisms that we have seen have all the ingredients that we usually require to call something “life”:

Darwinism

Darwin’s original book on the origin of species

in the Melbourne Museum of Natural History/Australia .

We have now arrived at a point where we can introduce the principle of Darwinism. This principle basically says:
If there is an organism that can replicate with mutations, and if this process continues for a long time, then those mutations that ensure the most successful replication will prevail.
Let us take an example. Let’s suppose we have one RNA strain that curls up, and another RNA strain that takes the form of a long string (this example is made up). When the cell divides, the division cuts the cell space into two random compartments. While the “curls” will most likely end up in one compartment, the “strings” may be cut in two. Now let’s say you take 100 cells with curls and 100 cells with strings. Let’s say they all replicate, so that each cell contains two of them. When the cells divide, the curls will end up unharmed. However, let’s say that half of the strings are cut in two by the cell division. Thus, we have 200 curls and 100 strings. Now the RNAs replicate again, giving us 400 curls and 200 strings. Again, all 400 curls survive, but only 100 strings survive. We see where this is going: While the curls will become more numerous, the strings will stay at 100 individuals. Now let us say that 10% of the cells suffer random destruction by mutation, chemical reactions, and physical impact in each cycle. Then the curls will double in each cycle, and then lose 10% of its individuals. The strings, in contrast, will be reduced in 50 steps to 0 individuals. Thus, the curls prevailed. After 50 steps, there will be only curls.

If you think about it, the principle of Darwinism is trivial: Whatever works best prevails. Whatever else there is dies out. Technically, the principle of evolution is a rule. Given a certain population of individuals, and given knowledge about which mutations ensure that the copies will survive, the rule predicts which population will prevail. The process of a changing and thereby surviving population is called evolution.

Darwinism was first developed by the British scientist Charles Darwinism in his 1859 book “On the Origin of Species” Darwinism.

Ribosomes

A ribosome producing a protein Bensaccount @ Wikipedia
At this stage of the early Earth, we have a number of cells that divide randomly, and that copy their RNA. Through the process of mutation, the cells formed variants. Some variants would be crushed by the elements, others would prove more stable. This process would favor variants that are more resistant to the environment, and faster in their replication cycle.

Over time, cells became more complex. Some cells would start interacting with proteins. Some RNA strains would attach certain proteins to their cell wall, others would collect certain proteins in the interior of the cell, and again others would use proteins to shape the cell. Thus, the population of cells with proteins would become much more varied. Eventually, one random mutation would create a protein called a ribosome Ribosome. Ribosomes can assemble other proteins from RNA strains. The ribosome maps each sequence of 3 nucleotides in the RNA strain to one amino acid in the protein. Thus, the RNA can essentially dictate which proteins to create Translation.

RNAs with a ribosome are able to create almost arbitrary proteins with arbitrary chemical properties and functions. These proteins can be free-floating, or they can attach to each other. They can be built so that they attach exactly to one particular other protein. This allows the cell to build up complex structures. It is as if you owned a 3D printer. The best thing about it is that the RNA encodes which proteins to produce. Thus, any copy of the RNA will build the same proteins. A sequence of nucleotides in an RNA that fulfils such a function is called a gene. The genes determine the build-up and the operations of a cell.

From now on, we will no longer speak in terms of atoms or molecules, but in terms of proteins. The proteins in real cells consist of hundreds of amino acids. They take complex 3-dimensional forms, and they can have complex, yet well-defined interactions with other proteins. Today, the RNA strains can be selectively modified in the laboratory, so that cells produce certain proteins or inhibit others Team Heidelberg: Phips in the Page / Technical Background, 2008.

Evolution of cells

The cell wall of an e. coli baterium, colored David Goodsell
Simple cells are just a vesicle plus an RNA. Later, ribosomes allowed the cells to produce almost arbitrary proteins. It is clear that RNA strains that teamed up with ribosomes had an evolutionary advantage. Over time, they would replace the strains that did not have this capability. Such cells would actively produce all types of proteins that fulfill all kinds of functions. Later, RNA strains would get replaced by DNA strains. These fulfill similar functions, but reproduce much more reliably.

This way, cells evolved into prokaryotes — simple single-celled beings. Prokaryotes continue to exist today. In fact, prokaryotes are the most diverse and abundant group of organisms on Earth and inhabit practically all environments where the temperature is below +140 °C. They are found in water, soil, air, animals’ gastrointestinal tracts, hot springs and even deep beneath the Earth’s crust in rocks. Practically all surfaces that have not been specially sterilized are covered by prokaryotes. The number of prokaryotes on Earth is estimated to be around five million trillion trillion, or 5×10^30, accounting for at least half the biomass on Earth. microbe

Prokaryotes include for example bacteria. Bacteria can be seen under the microscope. They are a reasonably well-understood form of life. Many of the proteins in a bacterium have been identified Bacterial cell structure. They are a proof that life can go on just by chemical reactions. Other types of single-celled life include fungi and algae. All of these are just collections of molecules, which continuously react with each other. These continuous reactions are what we call “life”.

It might be surprising to see what complexity a single cell brings with it. Yet, the process of cell evolution did not happen over night. Cells evolved over 2 billion years of time. This means that half of the time of the existence of Earth was needed just to get complex cells working.

Locomotion

Chemotaxis
A bacterium is a complex cell. The flagellum is a string of proteins that comes out of bacterium like a tail. It actually rotates. This rotation is powered by a chemical reaction: There is a concentration gradient in protons (not: proteins) between the interior and the exterior of the cell. This causes a constant flow of protons across the cell membrane. This flow, in turn, rotates the flagellum. The flagellum can rotate up to 10,000 times per minute.

This process moves the bacterium forward — up to a speed of 17cm per hour. This does not seem much, but is 60 times the length of the cell per second. The speed of the process can be regulated by changing the concentration gradient and thus the flow of protons. The direction of the rotation is controlled by a protein at the stem. When the flagellum turns counter-clockwise, the bacterium moves in one direction. When it turns clockwise, the bacterium just tumbles in place. The swimming of a bacterium is a sequence of tumble moments and swimming moments.

Bacteria need glucose (a molecule) to power these motions. This is their food. The bacterium swims in a liquid in which glucose is solved. The higher the concentration of glucose, the faster the bacterium can work and reproduce.The bacterium finds glucose as follows: It has a glucose receptor on the side opposite to the flagellum. Whenever a glucose molecule attaches, the bacterium switches to “swim” mode. Since the receptor is at the opposite side of the flagellum, the swimming happens in the direction of the glucose Team Heidelberg: Phips the Phage / Background, 2008. After some time, the glucose molecule detaches, and the bacterium switches back to “tumble” mode. It tumbles and changes direction until a new glucose molecule attaches. Thus, when it swims in the direction of increasing glucose concentration, it will swim more often and tumble less. If it swims in the other direction, it will swim less and tumble more. This leads to a random walk, which is slightly biased towards the direction of higher glucose levels. If this process is repeated, the bacterium will eventually swim to the source of the glucose Chemotaxis. That is: Those bacteria that managed to do this reproduced faster than those that did not have this capability. Therefore, they eventually prevailed.

It might seem close to unbelievable how such a complex mechanism evolved. However, remember that the DNA can encode and produce nearly arbitrary proteins. Through mutation, the cells would “try out” different proteins. Any design that gives a bacterium just the slightest advantage over other designs would have dominated the others. In fact, the flagellum is built up from the stem. New proteins are produced, and these assemble at the tip of the stem, thus prolonging the tail until it becomes a full flagellum (see Biologos: Self assembly of the bacterial flagellum for an explication by believers for believers; see Biologos: Complexity of life for a refutal of the concept of irreducible complexity). All in all, the evolution from cells to bacteria took 1 billion years — 5 thousand times longer than humans exist.

Today, the mechanism of locomotion in bacteria is reasonably well understood, down to the level of proteins, molecules, and atoms. The exact proteins involved in this process are catalogued here: Seesandra V. Rajagopala et al: The protein network of bacterial motility. Molecular Systems Biology, 2007.

Intention

We have seen how a bacterium moves towards higher concentrations of glucose. The process seems kind of intelligent, because the bacterium manages to swim towards the glucose even though it has only limited steering capacity. And yet, the process is entirely chemical. It would be easy to build a robot that shows the same behavior, and moves, say, towards the light. It is all just a purely mechanical procedure with no kind of thinking involved.

And yet, we have a tendency to say that the bacterium “wants” to move towards the glucose. What we mean is: Moving towards the glucose is beneficial for the reproduction of the bacteria. Therefore, those bacteria that moved towards the glucose prevailed over those that did not. Hence, any bacterium that we see today is hardwired to show this behavior. The behavior is no more voluntary than water flowing down a river: Both processes are entirely driven by physical and chemical laws, and are predictable. Still, we have a tendency to say that the water “wants” to flow downhill. Therefore, we shall now use the word “to want” to mean that a system is hardwired to show a certain behavior.

Multicellular organisms

We have seen how cells evolved, and how they became complex enough to become autonomous and self-moving organisms. The more complex organisms that we know consist of several cells. In particular, multicellular organisms consist of several types of cells, which each fulfill a particular function. The question is now how these came about.

Science has not yet found a conclusive answer to this question. All we know is that multicellularity evolved several times independently in several organism species. Not all of these evolutionary paths led to functional organisms. There are several hypotheses as to how cells first started grouping together Multicellular organism. The one that is considered most plausible is that multicellularity evolved from several cells of the same species that cling together. This may happen either because the cells fail to separate, or because separate cells of the same species attach to each other. Over time, the cells specialize: Some cells lose some functionality, and concentrate on one particular functionality instead.

This process can be observed in dictyostelids. Dictyostelids are amoeba, i.e., unicellular organisms. When food is readily available, they are individual amoebae, which feed and divide normally. However when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium, grex, or slug. The slug has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate Dictyostelid. This composite organism then moves towards areas of higher food concentration. Different cells take different roles in this process, and so we have a truly multicellular organism.

The question is now how this multicellular organism reproduces. For this to happen, the organism must duplicate, and make sure that all different cells are formed in their respective places. The amoeba does this as follows: Under the correct circumstances, the slug matures and forms a sporocarp (fruiting body) with a stalk supporting one or more sori (balls of spores). These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available Dictyostelid. That is: The multicellular organism serves as a host for baby amoeba. These baby amoeba are independent unicellular beings. However, when they are released, they may cling together and form again a multicellular being, in which they specialize to take one particular function. Thus, the amoeba by themselves are kind of the stem cells of the multicellular organism.

This process is an entirely chemical process, which has been discovered and analyzed. When an amoeba is stressed, it sends out a Cyclic adenosine monophosphate (cAMP) molecule. When another amoeba detects this molecule, it moves towards the concentration of this molecule. This leads to an aggregation of amoeba. Each of these also starts sending out cAMP molecules, thus calling even more amoebas. The entire DNA of the dictyostelid amoeba has been mapped and published. It contains around 12,500 genes. Thus, the entire process of how this multicellular being evolves has been catalogued.

Other organisms have developed more direct ways of replicating. The Nematode, e.g., is a worm that consists of 959 cells. These are generated in the egg, and each of them is specialized to take a certain function. The cells then move to their spot in the worm, forming the animal.

in the Science Museum in Chicago/US

Evolution

Evolution

We have seen how multicellular organisms evolved from simple molecules. The theory of evolution says that this process continued, and that all living beings evolved from these basic beings. In the form of a rule, the theory of evolution is:
For any species (contemporary or ancient; simple vesicles excluded), there is a previous species from which this species evolved through gradual mutation.
The theory says that we can trace the path from all contemporary species back down to simple vesicles. Vice versa, the theory predicts that simple beings evolved into more complex beings, and finally into the plants and animals that we know today. Living beings first evolved in the water, and later conquered also the land. Gradually, the beings became more complex: Fish, insects, dinosaurs, birds, and mammals evolved. The figure below illustrates the process of evolution on a timeline.

The timeline of life LadyofHats @ Wikicommons

But why would this be so? The principle that governs this process is natural selection.

Natural Selection

The principle of Darwinism says that, given a species that reproduces with mutations, the most beneficial mutations will prevail. This principle applies not just to cells, but to any species. The following traits can play a role:
Speed
If one individual can move faster than another individual, and if both are chased by a predator, then the slower individual will be eaten and the faster one will survive. Thus, the faster one has a higher chance of passing his genes on to the next generation. Thus, the next generation will, on average, be a tiny bit faster, too. Then the same effect happens in the next generation, and so on.
Adaptation
If one individual has a slight advantage over another individual (say, it has slightly longer fingers and can cling slightly better to tree branches, or it has a bit more fur and is protected better against the cold), then this individual will fare slightly better in life. It will have more chances to find food and to escape predators. Thus, it will have a slightly greater chance of passing on its genes, meaning that the next generation will also have this trait. If this is iterated for millions of individuals and for millions of years, eventually this trait will become even stronger.
Mating
If one individual is slightly better at mating than another individual (in whatever form), then the former will reproduce more often than the latter. Thus, its genes will prevail.
Resistance to illnesses
If one individual happens to have a mutation that makes it resistant against a certain fatal virus, and if this virus strikes the group, then only this individual will survive. Thus, any following generation (if any) will inherit this particular mutation. Note that this applies only to illnesses that appear before mating. Illnesses of age (such as Alzheimer) will not be eradicated this way, because they do not influence the reproductive success of the individual.
Every single individual and every single mutation is just a very small component in the game. A given individual with a disadvantageous mutation may still have more reproductive success than an individual with a better trait. However, if this experiment is repeated over millions of individuals, and millions of years, then the advantageous traits will prevail. It’s just like when two teams play football, and the ground is slightly sloped towards one of the goals. Of course, the downhill team can still win. However, when the teams play a dozen matches, it is more likely that the uphill team wins a bit more often. Now, evolution is actually more unfair than this: If a species is better adapted, it reproduces more frequently. In the analogy with the football game, this means: With every match that the uphill team wins, we make the slope just a tiny bit steeper. Of course, this will accelerate the process. The more the team wins, the steeper the slope will become, and the easier it will be to win again. In the end, the place will be vertical, and the downhill team has no chance whatsoever to win.

This process is called natural selection. It is powerful enough to change an organism completely. A species can grow wings, develop fur, gain more brain mass, learn certain behaviors, or adapt to certain climates. This is the process of evolution.

The Tree of Life

The tree of life, based on the Tree of Life web project (click to enlarge) LadyofHats @ Wikicommons
The theory of evolution says that all beings evolved by gradual change from previous beings. This does not mean that there would be one string of beings, in which each comes later than the other. When one population of beings becomes so different from the others that they do not reproduce with them any more, then this population forms a separate branch. This branch evolves on its own without interference from the other branches — it becomes a species. This process yields a tree-like structure, in which one branch evolves, eventually splits up into several branches, and these evolve again, only to eventually split up again. This structure is called the “phylogenetic tree”, or simply the “tree of life”.

Somewhat counter-intuitively, the major branches are not, say, birds, mammals, and plants. Rather, the branches are Bacteria, Archaea, and Eucaryota — rather obscure life forms, which are mostly invisible to the naked eye, but highly diverse and extremely numerous. It is estimated that bacteria and related life forms alone make up half of the biomass on our planet. Animals are in the branch of Eucaryota. In this branch, we find birds, insects, and mammals. Further down the branch of mammals, we find humans. In the figure, the root of the tree is in the middle. Humans are in the segment of Eucaryota (upper left, in pink), second from the right.

This tells us that evolution is not a linear process. Birds are not in any way “less developed” than humans. Both humans and birds evolved on their respective branch. The fact that they coexist today means that they are both equally well adapted to the environment of today.

Evolution is also not finished. It goes on and on. Every newborn animal has some slight mutations in their genes when compared to their parents. Animals develop resistance to bacteria, develop capabilities to compete with newly arriving competitor species, or change their physical traits to adapt to the environment. Humans, too, continue to evolve. For example, Europeans have evolved a tolerance for dairy products into adulthood, whereas people in China and most of Africa have not NBC News: 7 Signs of Evolution in Action.

The fossil record

Fossil of a Trilobite, around 500m years ago James L. Amos @ National Geographic
The theory of evolution says that all living beings evolved gradually from previous beings. Why should we believe this theory? Basically because it has made only true predictions so far. For many organisms, alive or extinct, we have found fossils or other remains. These include traces of multicellular organisms in stone, imprints of plants, insects enclosed in amber, skeletons. Fossils can also consist of the marks left by an organism, such as tracks or feces. Over time, scientists have found thousands of fossils. Wikipedia maintains a list of the discoveries List of transitional fossils. These include animal fossils, plant fossils, and also fossils of more basic life forms.

Fossils tell us a lot about an organism. From the skeleton of an animal, we can tell whether it moved on two legs or on four legs. From the shape of the feet, we can tell whether the animal lived on the trees. From the teeth, we can tell what the animal ate. From the size of the skull, we can tell the brain size. From the shape of the joins, we can determine the possible movements that the animal could perform. From the size of the bones, we can determine the amount of muscles that the animal had. The fossils can also be dated. One of the techniques to do that is radiometric dating. We date the rock layers above and below the fossil and thus estimate its age. We can also use nearby fossils with a known age to estimate the age of a fossil.

Fossilization is a rare occurrence. The conditions must be just right in order for an organism that dies to become fossilized, and for somebody to find later, which is also a rare occurrence. The theory of evolution does not actually say that we will find fossils of all species (some have not been found yet). It just says that if we do, its age will fall between the less and more evolved species. This theory is falsifiable, because if we find a species outside the time range, the theory is false. J.B.S. Haldane famously stated that “fossil rabbits in the Precambrian” would disprove evolution. So far, we have not found a fossil that would break the principle. This is a strong performance: We have discovered thousands of fossils, which span 4 billion years. Not one has been found that contradicts the theory. On the contrary, the theory of evolution correctly predicts the properties of the fossils that we find. The theory is thus validated in millions of cases. Therefore, scientists assume the theory of evolution to be true. The more fossils they find, the more they complete our picture of the entire process of the development of life — from the first single-celled beings up to the predecessors of humans.

Paleogenetics

The DNA is a sequence of nucleotides that determine the behavior of an organism. DNA sequencing is the process of identifying these nucleotides. This is a lengthy process that is done by expensive machinery and can take several days. The DNA of a human, e.g., contains 3 billion nucleotides. Nevertheless, the DNA of hundreds of species, including humans, have been completely sequenced. All species in the tree of life have been sequenced, meaning that we know exactly which genes these beings possess. The analysis of genes of different species is an ongoing process, and Wikipedia maintains a list of species whose genes have been sequenced List of sequenced animal genomes.

Paleogenetics is the study of genes (DNA) in fossils. Since every cell of a living being carries its DNA, this DNA can be recovered even from tiny fossil parts, such as a bone part. Since the fossils are usually millions of years old, the material has degraded, and has been invaded by bacteria and other microorganisms. Thus, of the DNA that is recovered from a fossil, only around 5% is actually useable. By overlaying parts of recovered DNA from different fossils, scientists can reconstruct larger parts of the DNA strain. For example, the genome of the Neandertal humans was sequenced to 50% in 2010.

Once the DNA of some individuals has been sequenced, the DNAs can be compared. The closer the two individuals are in the tree of life, the more DNA they share. For example, a human baby and their mother differ only in roughly 1 out of 60 million genes. Any two humans differ in 1 out of 1000 genes. A human and a chimpanzee differ in 1 out of 100 genes, and so on. Since we often know which parts of the genome are responsible for which part of the body, we can often tell how two species differ physically — just by looking at the genes.

The DNA sequencing can tell us not only how similar two species are, but also when two species became distinct. By looking at the number of mutations necessary to move from one DNA to the other (a technique known as the molecular clock), we can estimate the time at which a branching occurred in the tree of life Molecular clock.

The DNA contains copies of part of the DNA of the father and the mother of the individual. This tells us not just how the father and the mother were, but also how similar these were among themselves. This, in turn, sheds light the social structure of the species, by telling us whether the species mated within family clans.

Paleogenetics can tell us how similar one fossil individual is to another. All discoveries that we have made so far validate the theory of evolution: Similar organisms lived in similar times. We have not found one fossil so far where the paleogenetic analysis would have contradicted the theory of evolution.

Extinction

The tail of a hadrosaur, 72m years old, 5 meters long The Guardian 2013-07-23
The tree of life traces which species evolved from which other species. This does not mean that all species would still be around. Some species disappeared completely. Over the past 4 billion years, thousands of species have evolved only to become extinct a few million years later. The most prominent example are dinosaurs: they are species that evolved, but then died. In fact, 90% of all species that ever lived became extinct Neil deGrasse Tyson: Intelligent Design is Stupid, 2009-09-15. Youtube.

Hundreds of other species became extinct due to human intervention. They were hunted to extinction, or their life environment was altered so that they died collectively. Hundreds of species are currently at the edge of extinction. The International Union for the Conservation of Nature (IUCN) maintains a list.

Other species became extinct before modern humans. The Neanderthals, for example, were a branch of humans that lived 250 thousand years ago. They died out 200 thousand years later. As predicted by the theory of evolution, a species that became extinct never re-appears.

Some species are pushed to the edge of distinction, but then recover back to a larger population. For example, hundreds of years ago, tens of millions of American Bisons roamed the American prairies. Humans hunted the bisons down, and in 1890, only 750 individuals remained. Yet, the population recovered to several hundred thousands today. Similarly, the population of the northern elephant seal fell to about 30 individuals in the 1890s. Yet, dominant bulls are able to mate with many females — sometimes up to 100. Hence, the population has since rebounded. Whenever a population goes through such a bottleneck, the genetic diversity is cut down severely, and the remaining animals are more similar among each other Population bottleneck.

Oddities of evolution

The evolution of whales Biologos
Given any population of species, the ones with beneficial traits have more success in finding food, surviving, and mating. Hence, they prevail, and give their traits to their offspring, This means that the species as a whole develops this trait.

Evolution is not a goal-oriented process. It’s not that someone sat down and said: Let’s give feet to mammals, so that they can run. It’s more like: Those animals that had any means of propulsion (pushing themselves forward, curling their body, etc.) were more successful than those who did not. Eventually, the ones with more efficient means of propulsion prevailed — those with legs. To prove this, we cannot point to mammals that have no legs — because both theories predict that mammals have legs, and indeed all mammals have legs. But we can point to mammals that have legs and do not use them.

These are for example whales. Whales live in the sea, but evolved from mammals on the land. This means that they developed legs when they lived on the land. Then they started grazing in the sea, and eventually moved fully to the sea. But they kept their legs. Indeed, whales have small leg bones. These do not protrude from the body of the whale, and thus provide no disadvantage, but they are of no particular use either. So, nobody sat down and said “Let’s give this whale legs that it does not use”. Rather, whales first developed legs and then lost them. This can be traced back through the fossil record, as we have found fossils of the intermediate stages of this process (shown on the right).

Such structures are common in nature. They are called vestigial structures Vestigial. The mole rat, for example, has eyes, but these are completely covered by a layer of skin. This means that the animal is blind Spalax. Nobody sat down and said “Let’s give this animal eyes and cover them up”. Rather, the animal developed eyes when it lived on the ground, and then when it proved advantageous to cover them, they covered up.

We discuss more such oddities later.

My absolute favorite piece of information is the fact that young sloths are so inept that they frequently grab their own arms and legs instead of tree limbs, and fall out of trees.
Douglas Adams in “The Salmon of Doubt”

Artificial Selection

What is this? Warut Roonguthai @ Wikicommons
We have seen that natural selection filters out disadvantageous traits from a population of individuals. This process can also be induced artificially. Consider for example dogs. Assume that we would like to have a large dog that runs fast, so that it can help herd sheep. Then all we have to do is take any population of dogs, select the dogs that run fastest, and breed them. The offspring of these dogs will have the fast-and-strong genes of their parents. Among these offspring, we select again those that run fastest, and we breed them. Eventually, we will generate a population of dogs that run fast. This may sound like a very disrespectful way to treat nature. However, it is what humans have done. We have large dogs that have been bred with the explicit purpose to herd sheep (the German shepherd dog). We have aggressive dogs that have been bred to protect their owners (bulldogs). And we have dogs that have been bred to be cute and cuddly (poodles). This way, humans have actively used the principle of selection and evolution to produce the species they want. They have produced species that did not exist before. Thus, the theory of evolution is a testable theory, in the sense that you can actually try it out by yourself.

And this? History for Kids
If you do not have the time to breed dogs (they take several years to mature), experiment with drosophila flies instead. These are the tiny flies that live on fruit. They mature and reproduce very quickly. It is also easy to induce mutation by exposing them to radiation (e.g., from an old television screen). If you select bizarre individuals and remove the normal individuals, and if you let the bizarre individuals reproduce, you can generate a population of bizarre flies: Flies with more than 6 legs, with no wings, with 3 eyes, and so on. This works so well that it is frequently used as classroom exercise (search it on the Web). In this accelerated scenario, too, the theory of evolution makes verifiable and testable predictions.

Artificial selection has been at work in some less obvious places, too. Have a look at the fruit on the top right. It is ball-shaped, yellow, and has big grains in it. Can you guess what this is?

This thing is actually a banana. It’s just a banana in the wild, as it used to be before humans bred it. Over centuries, humans selected the bananas with fewer seeds, with better taste, and with longer shape, and bred them. This has led to the banana as we know it today: long, seedless, and yellow. Why did this banana not evolve naturally? Because the human banana is unable to survive in the wild. It requires so much water that it can grow only in plantations.

As another example, consider the fruit on the right. Can you guess what this is? It is corn. Corn before humans started breeding it.

Thus, several of the animals and plants around us are actually results of targeted evolution and selection. The theory of evolution is not just validated through the fossil record, paleogenetics, and the oddities of evolution, but actually testable.

Humans

The evolution of humans

The tree of life for hominae Orangutan Foundation
We have seen how plants, bacteria, and animals evolved. We will now look into one particular branch of ancient animals: Those that evolved into humans. Humans are rooted in the branch of the great apes, together with orangutans, gorillas, and chimpanzees. They became distinct from the predecessors of chimpanzees around 5 million years ago. This is what the fossil record and genetic analyses tell us.

This does not mean that “humans stem from the ape”. It just means that both have a common predecessor. It’s like the ancient Celtic people: They originally lived in the alps, but eventually spread out all over Europe Celts. Some of them became Frenchmen, others became Englishmen. This does not mean that the French would be ancestors of the English or vice versa. It also does not mean that one would be “better” than the other. It also does not mean that the French and English are equal in all aspects. On the contrary, the French have developed a cuisine that is considered vastly superior to the English one. Furthermore, the common ancestry does not mean that there cannot be any more Englishmen, just because there are now Frenchmen. It just means that the French and the English have a common predecessor. And it is the same with apes and humans. As Y. N. Harari notes in his book Sapiens, this means that there must have been a single female in the past who had two daughters — one that became the ancestor of humanity, and the other the ancestor of chimpansees.

If God created humans from dust, why is there still dust?
Checkmate, Christians!
anonymous

Humans

We have seen that humans and apes share a common ancestor. From what we know, the evolution of humans was not a linear process. On the contrary, nature tried out different branches of humanoid beings. We show them here:

Human evolution Handprint

The vertical scale is in millions of years. Each bar represents the time interval spanned by recovered fossils associated with that species. Dotted lines indicate the conjectural evolutionary lines of descent. (Different paleo-anthropologists will connect these in different ways, while preserving the chronological sequence.) Under each species name is a list of the national or geographical areas where all or most of its fossil remains have been found. White numbers inside the species bars indicate the approximate count of distinct individuals in each species from whom fossil remains survive. This is considerably smaller than the number of fossil specimens, because a specimen can be a single tooth, bone or bone fragment Handprint. Wikipedia maintains a list of humanoid fossils Human evolution fossils.

It is important to understand that the individual species in the diagram are not independent sets of organisms like, say dinosaurs and birds. Rather, the species in the diagram are periods of time during a continuous evolution where certain physical features were prevalent. Thus, there is no clear-cut difference between, say, Ardipithecus ramidus and its successor, Ardipithecus anamensis. Rather, the two species blend into each other, with Ramidus individuals increasingly resembling Anamensis individuals as time progressed, until they finally became so different that we apply a new name to them. Thus, when we say that “Anamensis appeared”, we do not mean that a new set of organisms was placed on Earth, but that the children of the children of the children of Ramidus species had become so different from their grand-grand-grand parents that they qualify as a new species. One species usually occupies a time range of hundreds of thousands of years. This corresponds to tens of thousands of generations.

Interestingly, some of these actually overlapped geographically and temporally, meaning that different species of humanoids coexisted. We can imagine this like different types of dogs: They are all dogs, but they are all very different, and some of them are so different that they do not interbreed. In general, the following things happened throughout the evolution of the humanoids:

Finally, one branch of this evolutionary process came to dominate all other branches. This is the species to which we belong: Homo Sapiens.
Molecular evidence suggests that our common ancestor with chimpanzees lived, in Africa, between five and seven million years ago, say half a million generations ago. This is not long by evolutionary standards ... in your left hand you hold the right hand of your mother. In turn she holds the hand of her mother, your grandmother. Your grandmother holds her mother’s hand, and so on ... How far do we have to go until we reach our common ancestor with the chimpanzees? It is a surprisingly short way. Allowing one yard per person, we arrive at the ancestor we share with chimpanzees in under 500 kilometers. (That is the distance from Los Angeles to San Francisco, or from Paris to Amsterdam.)
Richard Dawkins in “Gaps in the Mind”

Ardipithecus kadabba (“Ardi”)

How Ardi might have looked based on the skeletons. Note the feet and the form of the face. Jay Matternes @ Wikipedia.
Ardipithecus kadabba (“Ardi”) is an ancient species that is assumed to be one of the earliest ancestors of humanity. Fossils of around 35 individuals of this species have been found. The Ardis lived around 4.4m years ago in Africa. They had a grasping big toe adapted for locomotion in the trees, suggesting that they lived on the trees. However, the skeletons suggest that the species lacked the adaptations of living apes for climbing vertically, hanging from branches, and walking on their knuckles. Instead, Ardis were “careful climbers” in the trees, and supported their weight on the palms of their hands while using the divergent big toe for grasping. At the same time, the feet, pelvis, legs, and hands are adapted also for bipedal locomotion, suggesting that Ardis were bipeds on the ground. The large flaring bones of the upper pelvis were positioned so that Ardis could walk on two legs without lurching from side to side like a chimp. But the lower pelvis was built like an ape’s, to accommodate huge hind limb muscles used in climbing. Ardis stood about 120 centimeters tall and weighed about 50 kilograms. Wear patterns and isotopes in the teeth suggest a diet that included fruits, nuts, and other forest foods. They had reduced canine teeth, i.e., two diamond-shaped teeth at the front edges of the mouth. These were smaller than those of a dog, but larger than those of a human. Ardi had about 20% of the brain size of a modern human, at 300 cm³ to 350 cm³. National Geographic: Oldest human skeleton, 2009-10-09; re-arranged

Ardi cannot be a common ancestor of chimpanzees and humans. Chimpanzee are specialised for grasping trees. Ardi’s feet are better suited for walking because the middle of the foot is more stable, while a chimpanzee’s foot is more flexible Ardi. Thus, it is assumed that Ardi was the first species to branch off from the grand apes, and to start the journey to become human.

Australopithecus afarensis

A reconstruction of Lucy. Note the thick neck and the more human feet.

in the Natural History Museum of Vienna/Austria

The Australopithecus afarensis is an extinct species that is assumed to be the successor of Ardi and one of the ancestors of of humans. The species lived between 3.9 and 2.9 million years ago in Africa. We will refer to it as “Lucy”, which is the name of the most prominent fossil of the species. Like Ardi, Lucy had reduced canine teeth, although they are still relatively larger than in modern humans. Lucy also had a relatively small brain size (380cm³ - 430 cm³) and a prognathic face (i.e. a face with forward projecting jaws). The curvature of the finger and toe bones approaches that of modern-day apes, and suggests that Lucy was able to climb trees. On the other hand, the loss of an abductable great toe suggests that Lucy was not able to grasp trees with her feet. It is currently being debated to what degree Lucy was able to walk like a human, but it is undisputed that she could walk on two legs. Males were most likely larger than females. If observations on the relationship between sexual differences and social group structure from modern great apes are applied to Lucy, then we can deduce that these creatures most likely lived in small family groups, consisting of a single dominant male and a number of breeding females. Austra­lo­pi­the­cus afa­ren­sis

A 2010 study suggests the hominin species ate meat by carving animal carcasses with stone implements. This can be seen as a first use of unshaped tools. With males standing at approximately 1.5m tall and weighing about 59 kilograms and females slightly smaller a 1- 1.2m and weighing 35 kilograms, the Australopithecus were certainly not the largest of animals. They may have been the prey of some of the early ancient big cats. The jaws and teeth of the Australopithecus are somewhat larger than the modern human but far smaller than those of monkey like the Baboon. They have small reduced canine and molar teeth. These teeth would have been suitable for eating but would not have assisted the greatly to attack predators. Designer Animals: Extinct Ancestors of the Baboon

Homo habilis

How Homo habilis could have looked. Note the reduction of body hair. Encyclopedia Britannica / Homo habilis.
Homo habilis a descendant of the Lucy species. Homo habilis lived around 2 million years ago in Africa. It is currently not clear how the species relates to the Homo ergaster and the Homo erectus species. It is commonly assumed that Homo habilis have rise to Homo ergaster, which later gave rise to modern humans. But the species may also have co-existed. They may also have interbred. While we wait for these things to be sorted out, we describe Homo habilis.

Homo habilis had a brain size of 550 cm³ to 687 cm³ — roughly half that of a modern human. These hominins were smaller than modern humans, on average standing no more than 1.3m, and weighting 32 kg. The hole for the spinal cord in was located in the centre of the skull base, showing that this species walked on two legs. Walking on two legs allowed the species to carry items or babies while moving. It would also reduce exposure to sun heat. Bipedalism allows the hands to take over other functions. The finger bone proportions of Homo habilis suggest the human-like ability to form a precision grip, thus allowing the species to take and hold an item. Chemical analysis suggests that this species was mainly vegetarian but did include some meat in their diet Australian Museum: Homo habilis. The loss of body hair took place between 3 and 2 million years ago, in parallel with the development of full bipedalism.

Homo habilis remains are often accompanied by primitive stone tools. As opposed to Lucy’s unshaped tools, these stone tools were intentionally shaped. Homo habilis used one stone to split a flint stone in two pieces, so that the flint stone had a sharp edge. These are the so-called Oldowan (or Mode 1) tools Oldowan. This is a crucial departure from previous species, and also a crucial difference from other modern animals.

Homo Ergaster

A reconstruction of Homo ergaster in the New York Museum of Natural History wallyg @ Flickr.
Homo Ergaster is a humanoid species that first appeared 2 million years ago in Africa. It is likely a descendant of the Homo habilis species. It is a descendant of the Lucy species, and an ancestor of modern humans. It is currently not clear how the Ergaster species relates to another humanoid species, the Homo erectus species, who lived at a similar time. They could have interbred, meaning that Erectus would also qualify as a human ancestor. Ergaster and Erectus could also be two branches of the same species that initially just differed by their location and later diverged. Homo erectus later emigrated from Africa to Asia, while Homo ergaster stayed there.

Homo ergaster was about 190 cm tall, and had a brain size of 700 cm³ to 850 cm³. These species made more complex tools than the Homo habilis species, the so-called Mode 2 (Acheulean) tools. These are symmetrically cut flint stones, which can be used as hand axes. Since Homo erectus had already emigrated when Homo ergaster developed these tools, Homo erectus did not benefit from this invention.

Most importantly, Homo ergaster was probably able to control fire. This is suggested by sherds. These sherds were made of clay, and this clay has to be heated to at least 400°C to be hardened this way. Homo habilis was probably not able to make fire. Rather, they probably used the hot ashes or burning wood from a forest or grass fire, and then kept the fire or coals going for as long as possible by adding more wood and plant materials many times each day. Natural sources of animal fats and petrochemicals that burn could also have been used to keep and maintain fires. Fire would have helped the species to defend themselves against animals, and to produce heat and light. Wikipedia / Making fire

Homo ergaster later evolved into the Homo antecessor. These species lived around 1 million years ago in Africa. Males were roughly 1.8m tall, weighted 90kg, and had a brain size of 1,000 cm³ to 1,150 cm³. Fossil finds indicate that Homo antecessor practiced cannibalism. Homo antecessor gave rise to Homo heidelbergensis, which lived until 200,000 years ago. Males were about 1.8m tall, and weighted 62 kg. The brain size increased to 1100–1400 cm³ — overlapping with the 1350 cm³ average of modern humans. The morphology of the outer and middle ear suggests they had an auditory sensitivity similar to modern humans and very different from chimpanzees. Branches of the Homo heidelbergensis emigrated from Africa and spread to Europe. Homo heidelbergensis

Homo sapiens

Homo sapiens Henry Neville Hutchinson et al @ Wikipedia.
Over 400,000 years, Homo ergaster evolved into Homo sapiens. The new species appeared roughly 200,000 years ago in Africa. Homo sapiens have smaller teeth than their predecessors. Homo sapiens are the only ape in which the female is fertile year round, and in which no special signals of fertility are produced by the body, meaning that it is not possible for a male to determine when a female is in her fertile period. As a consequence of bipedalism, human females have narrower birth canals. Consequently, childbirth is more difficult and dangerous than in most mammals, especially given the larger head size of human babies compared to other primates. For this reason, human females give birth when the baby is still premature (when compared to other mammal babies). This has two important consequences (Y. N. Harari: Sapiens — a brief history of mankind, p. 11): First, humans need to take care of their babies much more than other mammals. This is part of the reason for the complex social structures (families, tribes, societies) that we have built. Second, human babies can still be shaped considerably even after birth — through education and socialization. This education is absorbed, and continued in the next generation — much like genes. This may be part of the reason for persistence of religions and belief systems.

Biologically speaking, Homo sapiens generally have a larger fore-brain than their predecessors, so that the brain sits above rather than behind the eyes. The brain volume increased to an average of 1350 cm³ — over twice the size of the brain of a chimpanzee or gorilla. The relatively larger brain with a particularly well-developed neocortex, prefrontal cortex and temporal lobes, enables high levels of abstract reasoning, language, problem solving, sociality, and culture through social learning.

There is evidence that Homo sapiens started wearing clothing roughly 100,000 years ago. Around 70,000 years ago, Homo sapiens emigrated from Africa — initially probably just with a few hundred individuals, leaving behind the other ones. The successors of these emigrated individuals arrived in Europe, and then in Asia (40,000 years ago) and the Americas (14,500 years ago). The larynx and hyoid bone descended in the species, thus making speech possible. Elements such as language, music and other cultural universals developed roughly 50,000 years ago. The species also started developing arts and manufacture. The first artifacts (little figurines) are dated around 40,000 years ago. The first cave paintings appeared 30,000 years ago (shown right). The species also controlled fire, and started cooking their food. Cooking food makes it more easily digestable, thus allowing humans to spend less time chewing the food. It may also have contributed to shorter intestine tracts, and thus to less energy consumption in that organ (Y. N. Harari: Sapiens, p. 14).

Paintings in the Chauvet Cave in France Thomas T. @ Flickr
Until 10,000 years ago, Homo sapiens lived as hunter-gatherers. At this time, they started agriculture, domesticating plants and animals, thus allowing for the growth of civilization. They used metal tools. About 6,000 years ago, the first proto-states developed in Mesopotamia, Egypt’s Nile Valley and the Indus Valley. Military forces were formed for protection, and government bureaucracies for administration. Writing was developed around 5,000 years ago by the Sumerians. States cooperated and competed for resources, in some cases waging wars. Around 2,000 - 3,000 years ago, some states, such as Persia, India, China, Rome, and Greece, developed through conquest into the first expansive empires. Influential religions, such as Judaism, originating in West Asia, and Hinduism, originating in South Asia, also rose to prominence at this time. Inventions such as the press, and advances in astronomy, mathematics, philosophy, and metallurgy helped shape the daily lives. The Scientific Revolution in the 17th century and the Industrial Revolution in the 18th–19th centuries promoted major innovations in transport, such as the railway and automobile; energy development, such as coal and electricity; and government, such as representative democracy and Communism. With the advent of the Information Age at the end of the 20th century, modern humans live in a world that has become increasingly globalized and interconnected. The life expectancy has grown from around 30 years to around 80 years in some countries. Today, there are 7 billion individuals of the species Homo sapiens — this is us humans.

The evolution of humans continues to today. For example, some branches of humans have developed the genes that allow adult humans to digest lactose (milk), while others did not. Illnesses develop and sometimes die out as humans develop resistance to them. Mutations cause degenerations, and disabilities. Skin color evolves, as does weight and size. People in warm climates are often relatively slender, tall and dark skinned. Dark skin is less volatile to sun burn. Light skin pigmentation protects against depletion of vitamin D, which requires sunlight to make. Due to practices of group endogamy (i.e., mating within the same group), similarities cluster locally around kin groups and lineages, or by national, ethnic, cultural and linguistic boundaries. Human

People are just fish plus time.

Neandertals

How Neanderthals could have looked. Note the shorter and more muscular body. Memorial Museum
Modern humans have left Africa around 70,000 years ago. However, other hominin species had left Africa before, most notably Homo heidelbergensis. What happened to these? The other hominin species continued to evolve outside Africa. Over time, they became so different that they became their own species. Examples are the Neanderthals (in Europe and Asia) and the Denisovans (in East Asia). The Neanderthals appeared around 200,000 years ago in Eurasia, after the exodus of their predecessors from Africa. At this time, the North of Europe and Asia was covered with ice. It is estimated that there were about 70,000 Neanderthals at the peak of the population size. The fossils of about 500 individuals have been found. Neanderthals and modern humans share about 99.5% of their DNA.

Neanderthals had an average brain size of 1600 cm³ — larger than that of humans. However, they were also much stronger than humans, so that the ratio of brain to body was actually smaller than that of humans. Neanderthals were in many aspects very similar to humans. They developed tools and art, and buried their dead. Stone tools discovered on the southern Ionian Greek islands suggest that Neanderthals were sailing the Mediterranean Sea as early as 110,000 years ago. An analysis of Neanderthal teeth found traces of cooked vegetable matter, meaning that the species controlled fire and were able to cook. Neanderthal

What happened when the humans arrived in the land of the Neanderthals? This must have been a rather scary encounter, where the humans were confronted with other humanoids that were much stronger than themselves, and yet probably much more primitive. We do not know whether the species fought, lived alongside each other, or just mixed. We do know, however, that humans prevailed. We also know that humans and Neanderthals interbred. Until today, up to 2% of our genetic material is from the Neanderthals. This is true only outside Africa, because Neanderthals did not live in Africa.

6000 years ago God said, “Let there be light!”. A cave man who happened to be close looked around confused. Not seeing anything said “ok” and continued to hit a piece of flint with a piece of pyrite until it lit a fire.

God saw the fire and said: “It is good!”. The caveman said, “It is something that we have done for tens of thousands of years, you’re not a little late?”.

God, confused, asked, “Where do you come from? How did you come here without a creator?” And the man said, “This is funny, I was going to ask you the same question.”.

Complexity

Emergence

Nature offers a stunning range of shapes, patterns, regularities, and organization — and often these are very beautiful. Thus, we ask where these shapes and patterns come from. How did nature “organize herself”? In many instances, the process behind these patterns is emergence. Emergence is the rise of complex structures from interactions between smaller entities that themselves do not exhibit these properties. Interestingly, emergence does not require central coordination. We look at 2 examples here.

A snowflake SnowCrystals.com
Our first example are snowflakes. Snowflakes are very regular, symmetric, and beautiful structures. They form from water dust roughly 3km above the ground. When the water dust freezes, it forms ice crystals. When other water dust particles collide with this ice crystal, they will also become ice and stick to the initial cluster. Due to the form of the water molecules, individual crystals can only stick together in very specific angles. This constraint makes any water crystal grow in hexagonal shape. This entails that snowflakes have 6 arms, and every one of these 6 arms has again small arms that grow off in the same angle. The length of an arm is determined by an equilibrium of energy. For a certain surrounding temperature, there is a certain optimal length. When this length is reached, the arm splits in two smaller arms. As more crystals join, the snowflake grows.

Now the question is why snowflakes are so highly symmetric. How does each new crystal element “know” what shape the other crystals at the other arms chose? The answer is that the same physical and chemical conditions apply simultaneously at all points of the snowflake. If the snowflake is in a certain temperature, then each arm will grow to the specified length. This is not because one arm would talk to the other, but simply because this temperature is the same at all points of the snowflake. Add in that the crystals can only attach in one specific angle, and you get an identical process and hence an identical shape at all points of the flake.

The next question is why snowflakes are so different. Since snowflakes have higher density than air, they fall to the ground. In this journey, a snowflake will pass different heights at different temperatures. The snowflake may also be blown up again into higher areas, so that the sequence of temperatures is not necessarily monotonously increasing. Each temperature entails a different optimal arm length for the crystal growth. Thus, if a snowflake falls through temperatures A, B, C, B, C, D, it will first form 6 arms of the length given by temperature A, then each arm will split into 2 arms of the length given by temperature B, then the arms split into arms of length C, length B again, length C, and length D. The sequence of temperatures and the time that the snowflake spends in each temperature determines the shape of the flake.

Other crystals grow in a comparable manner. All of these processes are driven by purely local reactions: An individual crystal does not “know” how the others attach. It just attaches to its neighbor. There is also no central authority that tells each crystal where to attach. Each crystal just attaches where the chemical properties allow it to. Thus, we have a phenomenon where local behavior without central coordination leads to the growth of complex, symmetric, and beautiful structures.

Shapes generated by L-Systems SolKoll @ Wikipedia

Plants grow in a similar way. Each plant cell sees only its immediate neighbors. Depending on where these neighbors are, the cell replicates in a particular manner. If every cell does this, and all the new cells do this again, the resulting structure becomes symmetric and ordered. This process can be described by L-Systems L-System. An L-System can be seen as a rule that says how to grow a single point into a small shape. This rule is applied to an initial point, and then to all points of the resulting shape, and so on. In the biological world, cells can follow such a rule. This single local rule is applied over and over again, and finally yields a global shape. These systems can indeed generate many plant forms of nature (see picture). Again, a very simple local mechanism gives rise to a complex global structure.

Simulating Emergence

A cellular automaton with the rule “Color a cell if exactly one of the three cells above is colored”.
Emergence is the rise of complex patterns from simple components. We can also simulate the emergence of structure on a computer. This is often done by cellular automata. A cellular automaton looks like a check board (shown on the right). In the basic version, each cell can be either colored or white, and initially all fields are white. We start at the top of the checkboard, and color some random cells in the first row (in the figure, this is just one cell). Then, we proceed to the second row. A set of rules tells us how to color the second row. A rule can, e.g., say: If exactly one of the three cells above are colored, then the cell shall be colored, too (see the illustration on the right in red). Such rules can depend only on the neighboring cells in the previous row. This is a very simple mechanism, which we can imagine to happen also in nature: One protein can do one particular thing depending on what its neighbors do; or one ant does one particular thing depending on what its colleagues do. This process is then iterated (always with the same rules) down the checkboard.

Shapes generated by cellular automata. Note the plant shapes at the top in the middle, and the snow flakes in the middle Steven Wolfram: A New Kind of Science
The surprising thing is now that, depending on the choice of rules, very complex and beautiful patterns emerge (shown on the right). With very simple rules, we can create the patterns of the fur of a tiger Steven Wolfram: New Kind of Science / p. 336, the shape of a fern plant, the shape of a snowflake (if we start from the center), the currents of fluids (p. 380), the form of snakes (p. 415), the shape of leaves (p. 402), or the pigmentation of animals (p. 427). In each case, the rule is very simple: It is just an instruction to color one single cell depending on its neighbors. There are only finitely many of these rules, and we can even enumerate all possible sets of rules. The results, however, can be highly complex and beautiful. This shows that the application of local rules, where every cell looks just at its neighbors, can lead to global patterns.

It is relatively simple to come up with a cellular automaton that is able to reproduce a given shape (p. 824). This cellular automaton consists of a fixed set of rules of how to color the cells. When we draw any black-and-white shape on the checkboard, and run these rules, then they will copy the shape — whatever it is. Once the shape has been duplicated, we can continue applying the rules, and the shape will be duplicated again, and so forth. Thus, even if each cell is “aware” of only its immediate surroundings, the cells can still accomplish complex tasks such as the replication of an arbitrary shape.

Behavior

We have seen that a local process can lead to global organization. So far, we have looked only at static shapes. We will now look at dynamic behavior that emerges from the behavior of smaller units.

In the animal world, one example of smart behavior that emerges from local behavior is how ants find the shortest path to a food source. Initially, the ants just stroll randomly around their nest. When one ant finds food, it brings a piece of this food back to the nest. While doing so, it leaves a trail of pheromones. Other ants find these pheromones will follow them, and thus also find the food. Several ants will take several different paths to and from the nest. However, an ant will generally prefer to walk where it can smell the pheromones. The pheromones become weaker with time. Now, something very interesting happens: If there are two paths to the food, a shorter and a longer one, and each is followed by the same number of ants, then the ants on the shorter path will bring back the food much faster. Thus, their pheromone trail will be much fresher. This means that other ants are more likely to choose this path. Since these ants also leave pheromone, the shorter path will accumulate even more pheromones. Thus, even more ants will follow it. In the end, all ants follow the shortest path to the food. Here, a complex global problem (finding the shortest path between two points) was solved optimally by simple local behavior. In a similar way, ants routinely find the maximum distance from all colony entrances to dispose of dead bodies. With such mechanisms, a colony of ants achieves complex tasks such as constructing nests, taking care of their young, building bridges, and foraging for food.

Crucially, the solution to these problems does not require central coordination. The queen ant does not give direct orders and does not tell the ants what to do. Instead, each ant reacts to stimuli in the form of chemical scent from larvae, other ants, intruders, food and buildup of waste, and leaves behind a chemical trail, which, in turn, provides a stimulus to other ants. Here, each ant is an autonomous unit that reacts depending only on its local environment and the genetically encoded rules for its variety of ant. Ants are extremely simple organisms, who lack any memory or intelligence. And yet, collectively, they form seemingly intelligent structures, without the need for any planning, control, intelligence, or even direct communication between the agents. Swarm behavior.

Another example of complex behavior in the animal world is swarming. Swarming is the collective movement of similar organisms in a larger structure. Birds, for example, form swarms, as do fish and insects. From an evolutionary perspective, swarming has several benefits for the participating organisms. First, it may be more efficient to move in a swarm than to move alone. For example, geese in a V-formation may conserve 12–20% of the energy they would need to fly alone. Second, a swarm makes it harder for a predator to single out an individual prey. Any swarm member that stands out in appearance will be preferentially targeted by predators. Hence, fish prefer to swarm with individuals that resemble them. Swarms also improve the chances of an individual to find a mating partner. Swarm behavior

Now how do swarms form? Researchers have studied this questions through a variety of techniques. For example, they can film swarm behavior and try to model it by rules, they can modify an individual organism’s scope of vision, or they can introduce small robots that resemble the swarming organisms and observe the changes in behavior. It turns out that swarming is governed by 3 simple rules Swarm behavior:

  1. Move in the same direction as your neighbors
  2. Remain close to your neighbors
  3. Avoid collisions with your neighbors
Every individual organism just follows these principles — and the swarming behavior emerges. It has been shown that the organisms often consider only around 6 neighboring organisms. Thus, the process of swarming is governed by very local principles.

Simulating Complex Behavior

Elementary process can give rise to complex behavior. Such behavior can also be simulated by cellular automata. A cellular automaton looks like a checkboard, and in every step each cell is colored either black or white, depending on which of its neighboring cells are black or white. If we allow a rule to recolor a cell that we have already colored before, then the checkboard becomes dynamic.

An example of Conway’s Game of Life Wikipedia/Gospers glider gun
One of the most famous examples of a dynamic cellular automaton is Conway’s Game of Life, a system devised by the British mathematician John Horton Conway. In this automaton, every cell is either alive (= black), or dead (= white). In the beginning, we initialize the cells randomly as either alive or dead. Each cell interacts with its eight neighbors, which are just the cells that surround it. At each step in time, the following transitions occur: If this process is iterated, very complex dynamics occur (see animation on the right). Depending on the initial configuration, we can have reproduction (as seen at the bottom right of the animation), static behavior (the two squares at the top), oscillations (where the same shape periodically reappears, see the top of the picture), and complex interactions, where one shape moves to disrupt another shape. All of this happens only based on local behavior. Each cell just lives or dies depending on its neighbors — it does not “know” that it is part of a complex periodic system. This shows that local simple behavior can lead to complex global behavior. Conway’s Game of Life and its variations are today a field of research. Conway’s game of life.

Predictability

We have seen that local processes can lead to global patterns and organized behavior. Each of these processes is deterministic. If nature just proceeds by small deterministic steps, does that mean that the result is predictable? In particular, if humans really consist just of cells that follow simple processes, are human actions predictable? And if, in the end, brain activity is also just a pattern of neuron cell activity, are our desires, thoughts, and actions predictable? And if so, what would that mean for our notion of “free will”? We would not have such a free will after all then, if it’s all predictable.

We first observe that organized local behavior does not always lead to organized global behavior. It can also lead to very chaotic global behavior. To see this, consider again the cellular automata. These automata can draw very beautiful patterns on the checkboard. However, they can also lead to entirely chaotic patterns — patterns that show no regularity whatsoever. These patterns are “random” in the sense that they show no organization. They are arbitrary dots of black and white. Thus, local organization does not necessarily lead to global organization Stephen Wolfram: New Kind of Science / p. 315.

Now, since a rule can generate very random-looking patterns, it is not always easy to say whether any given pattern is actually really randomly generated (without a rule), or whether it is the result of a rule. Truly random patterns and organized patterns often look indistinguishable (see Stephen Wolfram: New Kind of Science / p. 551 and p. 553). Thus, given any phenomenon of the real world, it may be hard or even impossible to say whether it was generated by a local process or not.

Now assume that we found out that a certain phenomenon is governed by a local process, and assume that we even knew this process. Then, we may still be unable to predict its behavior on the long run. In the language of cellular automata: Given a rule, it may be impossible to describe what happens after the 100,000th step. There are cellular automata that show a behavior that is so complex that it cannot be described upfront by a mathematical function. In the terms of this book, it cannot be compressed. The only way to discover what happens after the 100,000th step is to actually run all steps from 1 to 100,000 and to see what happens. In the language of nature, this means that the only way to find out what happens in the future is to simulate the local processes of nature and to extrapolate them to the future. Since nature is very complex, such a simulation might actually not be able to run much faster than nature itself. Thus, the only way to find out what will happen in the future may be — to wait and see what will happen. In this sense, nature is unpredictable. Human actions, too, are unpredictable in this sense.

Nature is even more unpredictable than that, read on.

The unpredictable future

The white triangle seems to be disappearing as we go down in the process. Will it die out completely, or will it re-appear? Steven Wolfram: A New Kind of Science
We have seen that we can construct cases where the only way to predict an event is to wait until it happens. Yet, even if we can afford to just wait and see, we may still be unable to solve the grand mysteries of life. Consider again the cellular automaton. Some automata produce certain shapes (say, a white triangle, as shown on the right). These shapes may re-occur in later steps, or they may never occur again. In the picture, the white triangle appears several times in the beginning, but then disappears. Now consider the question whether the triangle will die out, i.e., whether there is a point in time after which this shape will never occur again. To answer this question, we could run the automaton and see whether the pattern disappears. But that would not prove that it disappears forever. It could reappear. The only way to find out whether the pattern really disappeared forever is to run the automaton forever. We can prove mathematically that it is impossible in certain cases to make a decision without running the automaton forever. The question is actually undecidable (in the information-theoretic sense of the word). This means that there cannot be a systematic way to find out whether a given pattern will die out or not. In the language of nature, this means: Even if we know the processes that govern nature, and even if we bring enough time to observe what happens, we may still be unable to decide whether a given event will ever happen or not — unless we are prepared to wait for an infinite amount of time. We may say that these automata may be a poor approximation of nature. However, the automata are also part of nature. So the bottom line is that there are things that we cannot predict.

A simple example makes this clear: Assume that it were possible to predict that there would be a revolution in a certain country. Then the government of that country would do everything to prevent that revolution from happening (hand out cash to its citizens, reinforce the security services, or even call elections). As a result, the revolution would most likely not happen. Thus, the prediction would turn out to be wrong. This is an example of a “level-two chaotic system”, where the predictions that one makes about its state can actually alter that state (Y. N. Harari: “Sapiens”, p. 168). Therefore, it is impossible to predict all events of the future.

This does not mean that it would be impossible in general to make any predictions. There are still lots of other cases where we can make a prediction. For example, we can imagine a very simple cellular automaton that just draws everything in black. Of course we can predict the future of this automaton. Or imagine that we throw a stone in the air. Of course, we can predict that this stone will fall back on Earth — no matter all the theoretical results of undecidability. It is this portion of reality that we try to understand.

Free Will

We have seen that there are things that we can provably not predict. This has an implication for the free will of humans Stephen Wolfram: New Kind of Science / p. 750. It means that even if human thought and action is determined by local processes, it may still be impossible to determine what a human will think or do. This unpredictability is what we commonly call “Free Will”. There are plenty of philosophical and religious connotations to the concept of “free will”, but for this book, free will is simply the fact that we cannot predict human behavior. Everything else is metaphysical decoration.

Free Will does not imply that we can never predict what a human will do. For example, offering a human money for a task will significantly increase the probability that the human will perform that task. Vice, versa, punishment will reduce that probability. This insight is the basis of secular morality.

Questions

What has all of this to do with atheism?

This chapter has described how the universe and life came about from a scientific point of view. Now how does this relate to atheism?

Atheism is the disbelief in supernatural beings. As such, atheism excludes the belief that the Earth and life were created by gods. Atheism does not tell us, however, what atheists believe about the formation of life and the universe. Indeed, we cannot make any such statement, because atheism is just disbelief in gods and does not preclude or prescribe any other belief about the universe (or about anything else, for that matter). Different atheists will have different views on this topic.

However, a popular view among atheists is that science is the best method to answer the questions of life and the universe. This is also the stance of Humanism, the particular brand of atheism advocated in this book. What science says on these questions is what this chapter outlined in the preceding sections. Thus, the preceding sections will likely appeal to a large number of atheists as a reasonable view on the formation of the universe.

Nobody would consider God the author of a faulty object. In the perfection, God might have shown himself. But the imperfection reveals nature.
Charles Darwin

How can you believe what you don’t know?

[Found in: Progressive Secular Humanism]
The theories about the universe and life in this book are quite complicated. Most atheists will not even know these theories. Then we may ask why these theories are presented as an atheist view point.

First, not all atheists believe in science. The only thing that unites atheists is their disbelief in the supernatural. However, it is fair to say that probably a majority of those who are explicit about their atheism see science as the primary method to gain knowledge about this world. Humanists, in particular, see science as the best method to learn about the world.

However, this does not mean that these atheists incorporate the entire scientific literature in their belief system. Nobody can do that. It just means that they believe that science is the best method to learn about the physical world. You can believe in the utility of science without knowing all scientific theories.

Science is not the truth.
It is a way to find truth.

How can you believe in science?

The theories about the universe and life in this book are quite complicated. Most atheists will not even know these theories. So why do people still believe in science? How can this blind belief be justified?

Scientific theories have a number of properties:

  1. Science is the observation of nature. This means that scientific theories are grounded in observations. Since they are grounded, they are falsifiable.
  2. Scientists get credit (and thus higher status and more money) when they show that a theory is wrong. Therefore, scientific theories are systematically subjected to attempts to prove them wrong. A theory that produces a false prediction is rejected.
  3. Scientific theories have to make at least one prediction to qualify at all. This means that they are applicable.
  4. De facto, scientific theories have to make a large number of true predictions before they are accepted into the scientific literature. Thus, the theories are validated.
  5. Scientific theories are usually verified in extensive experiments, where the conditions and the conclusions are closely controlled. Thus, scientific theories are testable.
As it so happens, these properties are exactly the properties that make a theory true. This holds almost by definition, because truth is the set of theories that make true predictions, and science discovers exactly these. We remember that a theory can never be proven true. We can only show that it makes true predictions, and no false predictions. Therefore, the above properties make a theory as true as it gets. We cannot make it more true. This holds regardless of the actual content of the theory: If a theory has been tested, verified, re-tested, and always found to make correct predictions, then the theory is a good approximation of truth — no matter what it is about. Since science does exactly this, Humanists believe that science discovers the truth.

Many people object to the scientific method. And yet, even these people use the fruits of science in their everyday life. However, it is inconsistent to reject science, but to use its fruits. For example, it would be impossible to produce plastic the way we do it if the theory of chemical reactions were wrong. We produce and use plastic every single day. This is a concrete outcome of the theory of chemistry. It would be nonsense to use plastic every day and to refuse to believe in the theory of chemical reactions. Likewise, the very same theory that explains how proteins are constructed from DNA also gives us modern medical drugs. It would be inconsistent to use aspirin, but to deny the theory of proteins, DNA, and cells. The aspirin we use is the fruit and the consequence of that theory. It is not possible to make aspirin without knowing the theory. In the same way, the theory that predicts the diletation of time is not only at the heart of the theory about the size of the universe, but also one of the ingredients of GPS satellites. It is not possible to shoot a satellite into space if (1) one does not know this theory or (2) the theory is wrong. We use GPS satellites every single day. They guide the navigation systems of our cars, locate us on a map on our mobile phones, and geotag the pictures we take with our digital camera. It would be non-sensical to use these things and to say that the science behind it is wrong. The science behind it is right. And it is the very same scientific method, and in large parts even the very same scientific theories, that explain life and the universe.

There’s nothing magical about science. It is simply a systematic way for carefully and thoroughly observing nature and using consistent logic to evaluate results. Which part of that exactly do you disagree with? Do you disagree with being thorough? Using careful observation? Being systematic? Or using consistent logic?
Steven Novella

Science has not answered everything!

This book has elaborated on several aspects of life and the universe that science can explain. However, there are numerous holes in the story. There are species we have not discovered, stars that we do not know about, and proteins that we have not mapped. On the metaphysical side, we do not know what was before the Big Bang (if anything), we do not know where the universe is going, and we do not know how the human brain and mind work. Since all these questions are unsolved, why do people still believe so much in science?

The first answer is that science has not discovered everything, but what it has discovered is at least validated and useful. Thus, even though science may have treated only tiny bits of the big questions, these bits are at least reasonably safe to believe in. There is no contradiction here: One can know something without knowing everything.

Second, even if science has not discovered everything, that does not entitle us to invent fairy tales for the parts that it has not discovered. It is better to build on the parts we know rather than to claim that we know what we do not know. We elaborate on this in the Chapter on the God of Gaps.

I freaking love science
Third, the parts that we know are growing at breakneck speed. Until 1000 years ago, people had not the slightest idea how the universe was shaped, how life evolved, or how cells work. 100 years ago, people knew about cells, proteins, bacteria, the galaxies, and evolution. 10 years ago, people had a pretty good understanding of life and the universe, but crucial bits were still missing. Today, we can trace nearly the entire history of the universe from the first nano-seconds after the Big Bang until today. We can also trace the entire story of evolution, from the atoms to humans. Many of the things that this book contains were not known at the turn of the millenium. New bits and pieces are added as I am writing this book. Thus, even though our picture may never become complete, it gets more and more complete with every day that passes.
It is those who know little about science who so positively assert that this or that problem will never be solved by it.
Charles Darwin, paraphrased

Science cannot answer everything!

This book bases its explanations of life and the universe on science. We can argue that this focus is in fact a reduction of the scope of human thinking, because there are things that are inherently outside science.

This book subscribes to a notion of truth that is based on perceptions. Anything that explains or predicts perceptions is recognized as valuable. These can be perceptions in the physical sense (such as what you see or hear), but they can also be psychological perceptions. For example, feelings, desires, and states of mind are all perceptions. Anything that can predict these perceptions is welcome. Thus, the theory of truth presented in this book goes beyond physics and biology. Parts of this area are covered by the sciences of sociology and psychology, or by common sense reasoning. For example, psychology tells us that a person who prays will feel more calm. This is a perfectly valid rule for this book, and hence a step towards truth. Thus, this book is not limited to physics and biology. It just turns out that these are the sciences that explain life and the universe best.

Then there is a large area that goes beyond perceptions. This is everything that has never produced any human perceptions. This is commonly called the supernatural. For this book, all that never produces perceptions is the stuff of stories and myths. These can provide inspiration or entertainment, and thus they have their role in human culture. However, they should not be confounded with truth.

How do you explain the paranormal?

[anonymous]
Many people are convinced that paranormal activities are happening all around us. How do we explain this in a purely atheist world view?

Dale Thomas asks back on Quora.com: How do you explain that in this age of ubiquitous recording devices, worldwide communication, and extremely well-developed scientific processes, no single credible, confirmable evidence has ever been put forth of all those amazing supernatural activities you assert are happening? All we ever get are blurry photographs and unreliable testimonies. That’s simply not enough. There is no evidence that religious miracles ever happen. We discuss this in detail in the Chapter on Proofs for God.

Now contrast that with the miracles that science produces. These are:

Different from the religious miracles, these miracles are out there for everybody to see. They actually continuously make our lives better. That is more than we can say of any religious miracle. Thus, if miracles convince you to believe in something, then you have all the more reason to believe in science.
The difference between a miracle and a fact is exactly the difference between a mermaid and a seal.
Mark Twain

Are humans just apes?

Fossils of humans in their different stages of evolutionary development

in the Melbourne Museum of Science/Australia

The idea that humans are just more developed primitive apes is not a vey flattering one. Hence, the idea is continuously being challenged. It is commonly pointed out that Evolution is nothing more than a theory, and that it is just one possible way to see things. So the question is: Can you really believe that we evolved from apes? And if so, do you have to believe it?

It turns out that you do not have much choice. If you look at the fossil record, you will see fossils of different types of apes. These fossils are just there, we cannot just say that they’re not (see picture). These fossils can be dated. Now bones do not just appear like that. They have belonged to a species. Once you have established that the fossils belong to a species, you are basically there: There existed different species, which resemble humans more and more as time progressed. The most recent fossils belong to our species. That’s it. There is nothing not to believe in this.

If different experiments give you the same result,
it is not longer subject to your opinion.
Neil de Grasse Tyson

Are some species better than others?

Progressive Secular Humanist
The Theory of Evolution says that species evolve, and that those that fit the environment better will outnumber those that don’t. This makes it sound as if some species were “generally better” than others. In particular, it sounds as if humans were “better” than other species.

In fact, the theory of evolution makes no such claim. It just says that those species who are better adapted will outnumber the others. Here, “better adapted” can mean anything: faster, smarter, larger, but also smaller or more resilient. Pigeons, for example, are perfectly adapted to the environment of modern cities: they are extremely resilient to pollution, can eat almost everything (no matter how toxic), and reproduce like crazy. In this respect, they are much “better adapted” than humans. It may well be that humans will one day exterminate themselves through pollution or war — while pigeons, ants, and rats are likely to survive. Thus, humans are not “generally better” than pigeons.

In fact, the theory of evolution says that humans are just species like all the others. It was religion that came up with the theory that humans would be special.

Is Evolution falsifiable?

This book makes much out of the concept of falsifiability. So the question arises whether the theory of evolution can be falsified.

It turns out that it can. The first possibility to falsify evolution is to find any fossil that does not fit into the tree of life. As B.S. Haldane’s observed: Any fossil rabbits in the Precambrian would immediately disprove evolution. So far, we have never found any fossil that would break the principle.

The theory of evolution also says that gene mutations are passed on through the generations of species. This means that any of the following would prove the theory of evolution wrong:

Charles Darwin made the case a little differently when he said, “If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.” Rationalwiki / Disproving evolution. Indeed, we have not found any of these counter-indications so far.

The principle of evolution is not just falsifiable, but even testable. You can, for example, take drosophila flies, and evolve them yourself. This is commonly done in biology classroom studies, but you can also do it yourself.

Evolution is just a theory!

The theory of evolution is called a “theory”. Doesn’t this already show that it’s not a fact?

Scientists use the word “theory” much in the sense that this book uses it: A theory is a set of rules that explain and predict the phenomena of nature. The theory is assumed to be true if (1) it is falsifiable, (2) it is applicable, and (3) it makes only true predictions. It is an even better theory if (1) it is testable and (2) it compresses information. As it so happens, all of this is the case for the theory of evolution:

  1. The theory is falsifiable.
  2. The theory has made individual predictions already.
  3. The theory is validated through the fossil record, paleogenetics, and the oddities of evolution.
  4. The theory is testable.
  5. The theory is compressive, because it basically explains the entire fossil record with a single rule.
Thus, we have every reason to believe that the theory of evolution is true. In fact, the theory accurately explains what we observe, and predicts what we will observe. This is more than any religious theory can say of itself.

For this, it does not matter whether you call evolution a “theory”, a “fact”, or a “hobblenock”. What matters is that it accurately describes reality.

Now scientists still call it a “theory”, and not a “fact”. This is because they are ready to abandon it, if it ever makes a false prediction. Again, this is more than any religious system can say of itself. In fact, everything in science is a theory. For example, the theory of gravity is a theory. This is because it could be that one day it makes a wrong prediction. It’s just that it doesn’t. And it is the same with the theory of evolution.

Anyone who believes that the laws of physics are mere social conventions is invited to try transgressing those conventions from the windows of my apartment. I live on the 22nd floor.
Alan Sokal

God did it!

One alternative explanation for the genesis of the universe, the Earth, and life is a supernatural one: “If something exists, then God did it”.

We discuss this explanation in detail in the Chapter on the God of Gaps. Here, we just note that this theory cannot be a true in the sense of this book, for the following reasons:

  1. It cannot be falsified. There is nothing that a believer would accept as a proof that God did not create a particular thing. This means that we can come up with arbitrarily many contradictory supernatural theories, which also all explain the birth of the universe. This is indeed what people do.
  2. The theory is not applicable, because it does not make any perceptible predictions whatsoever. It is for this reason that theologians have never ever come up with a correct prediction about this world that could not have been made by science.
  3. The theory makes assumptions (such as the existence of God) for which there is no evidence.
Thus, the theory is not true in the sense of this book. Apart from that, the theory does not compress information. All that the supernatural explanation can say about this world is “It is like that because God made it that way”. This, however, does not tell us anything more than what we knew anyway. Therefore, the theory has no explanatory power.

You cannot see evolution!

Opponents of the theory of evolution can argue that the theory is too abstract and hypothesizes only about the past. We have never witnessed how new species come into existence during our lifetime.

The theory of evolution makes some verifiable predictions that fall in our lifetime. We rely on them for the breeding of our food and domestic animals. The theory also makes falsifiable predictions on the types of fossils that we find. Peter and Rosemary Grant have studied how the body and beak size of Galápagos finches changes response to changes in the food supply, driven by natural selection. This happened fast enough to study it Peter and Rosemary Grant. The claim that different species may come into existence is harder to observe.

And yet, we can observe this effect as well BBC: Evolution — What the world’s youngest species can teach us, 2012-11-23:

  1. populations of periwinkles are evolving elaborate and different penises, which prevents them mating with other populations of snail, isolating them into different species.
  2. The Mimulus peregrinus flower is one of the youngest recorded, appearing less than 140 years ago.
  3. In the mid-1900s another new flower, Senecio cambrensis, naturally speciated in North Wales in the UK, while around the same time two species of flower Tragopogon mirus and T. miscellus appeared in Washington State in the US.
  4. in the latter part of the 20th Century, the flower species Cardamine schulzii appeared in Switzerland.
  5. The Senecio eboracensis flower evolved into a new species in the past 40 to 50 years, being discovered in 1979 in York, England.

Thus, new species do arrive, as predicted by the theory of evolution.

You can criticize evolution for making wrong predictions.
Note, though, that religion has yet to make any at all.

God created the Universe to look old

Science tells us that the Universe is 13.5 billion years old. Certain interpretations of the Bible tell us that the Universe is 6000 years old. One proposed solution to this is that God created the Universe 6000 years ago, but that he made everything look as if it were 13.5 billion years old.

Let me answer in the words of Adriana Heguy on Quora.com:

That God created the universe 6000 years ago to look much older is certainly possible. Just as possible as that we were all actually created 10 minutes ago, but we are all under the illusion that we have lived for twenty, or fifty years, and that there is a sacred book that says that the universe is 6,000 years old, and that there are fake artifacts to fool us into thinking that the universe is 13.8 billion years old, and that some dinosaurs evolved into birds.
The attentive reader will have noticed that any hypothesis about faked evidence is unfalsifiable: We would never be able to show that the evidence we see was faked. This, in turn, means that the hypothesis is meaningless: If we assume that the evidence was faked, we cannot draw any conclusion from it. We are as wise as before. Furthermore, we can come up with arbitrary other theories of faked evidence (as Heguy did), which contradict the first theory. None of them can be proven wrong. This all just confirms that unfalsifiable theories are nonsense.
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