50 Great Myths of Human Evolution

Understanding Misconceptions about Our Origins

John H. Relethford

• Publisher: Wiley-Blackwell
• Year: 2016
• ISBN:
  9781119308034
• Edition: 1
• Topic: Sciences sociales
• Subtopic: Anthropologie anatomique

50 Great Myths of Human Evolution uses common misconceptions to explore basic theory and research in human evolution and strengthen critical thinking skills for lay readers and students.

• Examines intriguing—yet widely misunderstood—topics, from general ideas about evolution and human origins to the evolution of modern humans and recent trends in the field
• Describes what fossils, archaeology, and genetics can tell us about human origins
• Demonstrates the ways in which science adapts and changes over time to incorporate new evidence and better explanations
• Includes myths such as "Humans lived at the same time as dinosaurs;" "Lucy was so small because she was a child;" "Our ancestors have always made fire;" and "There is a strong relationship between brain size and intelligence"
• Comprised of stand-alone essays that are perfect for casual reading, as well as footnotes and references that allow readers to delve more deeply into topics

1
IDEAS ABOUT EVOLUTION

In order to explore the myths of human evolution, we need to start with a brief review of how evolution works. It turns out that many of the myths of human evolution are related to misconceptions about the process of evolution in a general sense, starting with what is likely the biggest one of all—that evolution is “just a theory.” This section of the book examines some common misconceptions of the process of evolution.

Myth #1 Evolution is a theory, not a fact

Status: This is a myth based on a misunderstanding about the use of the word “theory” in the natural sciences. When we state something is a theory, such as evolutionary theory, atomic theory, or the theory of gravitation, we are not suggesting that it may or may not exist (a more popular use of the word “theory”). Instead, we are talking about a hypothesis that has been tested repeatedly and has stood the test of time without being rejected.

Of all the myths about evolution, perhaps the one that we hear more than any other is the idea that evolution is a theory and not a fact. Most often, this myth is expressed as the statement “It’s just a theory” or the somewhat longer “It’s a theory, not a fact.” By contrasting fact and theory, we are forced into an either‐or situation. Either evolution is indeed a fact or it is a theory. We then must choose between one side and the other. According to popular logic, if we accept evolution as a theory then it is not necessarily a demonstrated fact. The logic works here only if we define the word “theory” as an unsupported or unproven hypothesis or explanation. In other words, if we classify evolution as “just a theory,” it implies that evolution may or may not exist. In terms of human evolution (that aspect of evolution that tends to upset folks more than, say, elephant evolution because it is personal), the statement that evolution is “just a theory” means that humans may or may not have evolved. If we cannot tell, then evolution (including human evolution) is therefore not a fact. It is, according to this logic, at best an opinion.

Although much of the above may seem logical and perfectly reasonable, the argument rests on an underlying assumptions that “theory” means an untested hypothesis or mere opinion and that something can be either a fact or a theory. It turns out that our more popular use of the word “theory” is not what it means in the context of scientific thought. Evolution is actually both a fact and a theory. In my introductory course on biological anthropology, I ask the class on the first day to raise their hands if they think evolution is a fact. I then ask the class to raise their hands if they think evolution is a theory. I then tell them “Congratulations! All of you are correct. Evolution is both a fact and a theory.” This statement can cause some consternation in anyone who is used to facts and theories being considered in terms of an either‐or proposition. In order to see the mistake being made by this proposition, we need to consider a bit of the underlying philosophy and method of the natural sciences and explore briefly what we mean by fact, hypothesis, and theory.

To most of us, the definition of “fact” is pretty straightforward. A fact is a verifiable truth—something we can all observe and agree on. The key feature here is that facts must be capable of being verified. If I say that there are trees in my yard, you can actually look and see if this is true. Some facts are easy to verify and we will all agree with little or no argument. For example, if we drop an object, such as a pencil, it will drop to the ground. We call this fact gravity. Sometimes facts are contingent upon a more exact definition. In the case of gravity, the pencil would have to be dropped while standing on something of sufficient mass to generate sufficient gravitational force to attract the pencil. Sometimes facts are tricky because they are not directly observable with our senses. We can easily see a pencil dropping, but what of the fact that infectious diseases are caused by bacteria and viruses that are not visible to the human eye. Of course, we easily accept the existence of such microorganisms because we have developed microscopes and other technology to make our observations. However, imagine you were alive during the fourteenth century and someone explained to you that the Black Death (bubonic plague) was caused by a bacterium, something that could not be seen except with a microscope (that had not yet been invented). I suspect that most people at that time would have rejected this idea because the plague bacterium could not be observed with the naked eye.

Observing something, either directly with our senses or with technology, is a start in establishing a fact, but you need to remember that facts must be verified. Sometimes in the history of science, we find that our basic facts change when more observations are made. At one time, for example, it was thought that humans had 24 pairs of chromosomes, but over time, more advanced methods revealed that we actually had 23 pairs of chromosomes. At one time, a fossil known as Piltdown Man (discussed in Myth 13) was thought to be a fact supporting the then‐popular view that humans evolved large brains before losing certain ape‐like features of the teeth. In this case, inconsistency with other facts, development of better ways to date the individual fossils making up Piltdown Man, and other pieces of evidence pointed out that it was not a fact, but instead a fake. Someone (whose identity is still not known with certainty) faked the whole thing. Again, such lessons show us that science requires verification even with basic facts.

What about theory? Before considering the different meanings of the word “theory,” we need to start with the idea of a hypothesis. Science is not simply an accumulation of facts about the physical universe. We also try to explain what we see. A hypothesis is just a tentative explanation of the facts. For example, why does a pencil fall to the floor when I let it go? In order to make my point about the nature of a hypothesis and how it ties into science, I am going to state an obviously ridiculous hypothesis to explain the falling pencil. Imagine that I have placed a magnet inside the pencil and then held it over a spot on the floor under which I have buried a very powerful magnet. When I let go of the pencil, the magnetic forces cause the pencil to drop to the floor. I imagine as you are reading this, you are thinking that this hypothesis is one of the silliest things you have ever heard, and so ridiculous that even discussing it is a complete waste of time. Yes, it is ridiculous and it is clearly false, but the interesting thing here is that my wacky idea is actually a good scientific hypothesis because it can be tested. There are a number of ways to test this hypothesis. Break open the pencil or dig under the floor to find there are no magnets. Use a device (such as a compass) and fail to detect any localized magnetic force. Or, in perhaps the most simple but also most elegant test, drop your own pencil (or shoe or baseball) and find that they all drop to the ground without any magnets being placed inside of them.

In each case, the hypothesis has been tested and has been rejected. We then have to move on to another hypothesis. Each time we develop a hypothesis we try to determine some way to test it. Science is continually involved with the testing and retesting of hypotheses, looking for hypotheses that have stood the test of time. In the natural sciences, we use the word “theory” to indicate a hypothesis, or set of hypotheses, that has been tested repeatedly and has not been rejected. We might continue to refine the theory, but the basic elements are widely agreed upon and unlikely to change.

This definition of theory contrasts with the popular idea that a theory is a hypothesis or just a guess and that the subject of the theory may or may not exist. However, when you hear the phrase “theory of gravity,” do you think that gravity may or may not exist? Of course not. To take another example, consider atomic theory in chemistry. Does the inclusion of the word “theory” make you think, “Well, atoms are only a theory and they may or may not exist”? I doubt any reader takes this stand. The elements of atomic theory have been tested and have held up over time. The same is true for evolution. The basic ideas regarding the mechanisms of evolution (described in later myths) have been confirmed and form the basis for modern evolutionary theory. As with gravity and atoms, evolution is both a fact and a theory. Arguing that something has to be one or the other is a misuse of the scientific method.

Historically, we associate part of modern evolutionary theory with the insights of the nineteenth‐century naturalist, Charles Darwin, who contributed to our understanding of both the fact of evolution and part of the underlying mechanism for evolutionary change. By Darwin’s time, many in the scientific community were coming to grips with evidence showing changes due to evolution. The spread of the Industrial Revolution had led to increased mining and quarrying activity. As people dug into the earth, they found many fossils of creatures that did not fit nicely and neatly into their views on variation. Imagine, for example, you were digging in your backyard and found the skull of a cow. How would you explain it? Depending on where you live, the explanation might be very simple—perhaps your property was once a farm where cows lived and died. Or, imagine you unearthed a skull of a modern human. Although such a discovery might lead to all sorts of speculations about the identify and fate of the person you found, the simple truth is that finding a modern human skull in the ground is not likely to be an earth‐shattering discovery.

However, what would you do if you found the remains of a creature that no longer lived, such as the bones of a dinosaur? This discovery implies that there were creatures that once existed but have since become extinct (which turns out to be quite common—we now know that over 99 percent of all species that have ever lived have become extinct). How do you explain this extinction? You then notice upon further examination that the bones of the creature you discovered are similar to, but not identical to, living creatures. For example, if you look at fossil remains from many millions of years ago, you will find creatures that are clearly similar to horses, but instead have three toes on each foot, as compared with the single toe typically found in modern horses. Or, in the case of human evolution, we can go back 2 million years ago in Africa and find creatures that are very similar to us in terms of how they walked and their basic body anatomy, but have smaller brains and larger faces. As we examine the fossil record even further, we see examples of trends over time, such as a reduction in the number of horse toes or the increase in the brain size of bipeds. Such trends are clear examples of evolution (and more will be presented throughout this book). How do you explain such facts?

Darwin was one of those who sought an explanation for change over time. Darwin made two very important contributions. First, he collected data confirming the fact of evolution as revealed from field studies of living organisms, the fossil record, and the comparative anatomy of different species, among other sources of evidence. His result was a convincing argument that all living species were related through a process of what he termed “descent with modification.” The mechanism that Darwin proposed (natural selection) will be dealt with in later myths, but here we just focus on the fact that natural selection was a hypothesis relying on natural phenomena that explained the observed facts. As with all scientific hypotheses, Darwin’s idea has been tested repeatedly. Because it has survived without refutation, the concept of natural selection has been elevated to the status of a scientific theory. Once more, keep in mind that the word “theory” has a very specific meaning here and does not mean something that may or may not exist.

The final point about Darwin’s idea is that even though it forms part of modern evolutionary theory, his concept of natural selection is not the entire answer. Although Darwin got a lot right, he also had questions that remained unanswered during his life. The tentative nature of scientific explanation can be frustrating to those seeking a final definitive answer, but it is the basic nature of scientific inquiry with which we continue to refine our explanations. The theory of evolution is no exception. We do not have all the answers, but continue to seek them through the scientific process. However, although scientists continue to debate the details of the evolutionary process, there is agreement on both the fact of evolution as well as the basic explanation of how evolution happens. The details of the evolutionary process are described briefly in the next myth.

Myth #2 Evolution is completely random

Status: This is a myth because it implies that evolution is a chance event. Although some aspects of evolution (such as mutation) have a random element, other aspects, such as natural selection...