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Given the sad state of science education in our country, it should not be surprising to learn that many people have misconceptions about evolution. These misconceptions are nowhere more evident than in the publication and statements of "scientific" Creationists. This page is an attempt to clear up some of these myths.
Evolution is a theory, not a fact
This misconception has recently been the subject of a piece of Alabama legislation, known as the Alabama Insert. This legislation requires that all biology textbooks used in Alabama schools carry a warning to the effect that evolution is a theory, not fact.
The insert reveals a fundamental lack of understanding on the part of Alabama legislators on exactly what scientists mean when they talk about a 'theory'. In the world of science, a theory refers to a body of knowledge which is used to explain a particular phenomenon. Thus, we have theories of gravitation, optics and planetary motion. No-one really doubts that gravity exists, or that photons enable us to see, or that the planets orbit the sun in regular, well-defined paths. The word 'theory' in this sense does not connote, as some would have us believe, a guess, or a poorly supported hypothesis. The word simply refers to the entire body of knowledge, i.e. the observations, facts, experiments, and theoretical constructs that underlie and explain the observed phenomena.
Just as no scientist doubts the existence of gravity, so very few scientists doubt that evolution has occurred. Thus, they acknowledge the fact of evolution. The theory of evolution, on the other hand, details the attempts of science to find out exactly how evolution works. It is here that the dynamics of science come into play. Although the broad outlines of the theory are well understood, and well supported by evidence, the details, such as the tempo and mechanism of evolution are still the subject of debate.
This latter fact reveals another point about evolution that is frequently misunderstood, especially by Fundamentalist Christians. Such people are used to having a rigidly defined dogma, in which there is only black or white, and all facts are either true or false, with very little room for error or debate. Thus, they see scientists arguing among themselves about the finer points of evolution, and come to the conclusion that the theory is on the verge of collapse. Nothing could be further from the truth. Scientists realize that no theory, be it gravitation, quantum physics or electrodynamics, can be completely proven. All we can do is say that a particular theory is probably true, based on all available evidence. This leaves open the possibility that further information might require a modification of some of the details of the theory.
So it is with the theory of evolution - it is supported by multiple lines of evidence, from geology, paleontology, genetics and so forth. It is as well supported by evidence as any other field of science. Which is not to say, of course, that we have all the answers. Far from it. We know that there are gaps in our knowledge. The challenge is to fill those gaps.
There are no transitional fossils
This charge is almost always leveled by Creationists, and has even been the subject of a number of Creationist books and tracts. Basically, the claim is made that the fossil record shows the sudden appearance of complete species, and has no room for intermediate forms.
A basic problem with this accusation arises as soon as we try to answer the question of what exactly constitutes a transitional fossil. This point has never been fully addressed by the Creationist lobby, and so leaves the evolutionist at something of a disadvantage. For, as soon as the biologist points to a fossil, such as Archaeopteryx, which displays characteristics of both reptile and bird, the creationist simply reclassifies the specimen as a complete species, and then repeats his request for transitional forms.
The fact of the matter is that every fossil, and every organism on this planet today represents a transitional form. All organisms are part of the evolutionary tree, and even the end-points are still growing. We are all thus transitional forms, in every sense of the word.
If, however, the charge is that there are no forms which show elements of two or more established species, then this can easily be shown to be false. There are lists of such fossils available at the Talk.Origins home page. In addition, the transition from reptile to mammal, known as the therapsid series, is so well supported by fossil evidence that there is a lively debate over exactly where the reptile ends and the mammal begins. It should also be borne in mind that fossilization requires a number of specific conditions in order to occur. Fossilization actually occurs quite rarely, which explains why there are, and always will be, gaps in the record.
Humans are descended from apes
In fact, the theory of evolution holds that all primates descended from a common ancestor, not from each other.
The existence of living fossils disproves evolution
One frequently hears the objection "if evolution is true, why are there still crocodiles?" The fact is that evolution does not proceed in a straight line. A single ancestor could easily give rise to more than one sub-species, who then generate their own sub-species and so on. No rule says that the parent species must then go extinct (although this often happens).
So, the charge that is often made, for example, that Archaeopteryx cannot be a transitional form because it appears in strata with more modern birds is actually irrelevant.
There is no proof that evolution has happened
This myth is repeated so many times in Creationist literature that it has almost become a cliche. We frequently hear Fundamentalists asking for "proof of evolution", apparently confident that no such proof exists.
The fact is that abundant proof is available to show that evolution has occurred in the past, and still occurs in the present. For an example of modern evolution, no instance is more telling than the phenomenon of microbial resistance to antibiotics. This is exactly what has been predicted by evolution - since bacteria reproduce so quickly, we would expect to see mutations conferring a survival benefit upon the organism. In at least one case, geneticists have actually isolated the specific mutation that gave rise to a resistant strain of Malaria.
Strong evidence also exists to show that evolution has occurred in the past. The best such evidence comes from molecular genetics. Techniques such as DNA-DNA hybridization have shown that we share a lot of genetic material with our close ancestors. In most cases, this technique has confirmed the evolutionary tree that was previously built up on the basis of morphology alone. In other cases, the technique has revealed some surprising relationships, such as the fact that whales are most closely related to a certain class of land-going mammals.
Probably the strongest evidence from molecular biology is the phenomenon of shared genetic errors. For example, it is known that all primates lack the ability to synthesize vitamin C. It has now been shown that this is due to a crippling mutation in the gene that usually codes for vitamin C in other mammals. Most significantly, it has been shown that both humans and apes have precisely the same mutation in this gene. The only obvious answer to this phenomenon is a mutation in the common ancestor of all primates, including humans. Edward Max has an excellent article on this phenomenon. (It requires that you have a good working knowledge of genetics, but is well worth the effort.)
Links
The Talk.Origins Archive
Teaching
about Evolution and the Nature of Science - Published by the
National Academy of Sciences
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