Carl Sagan once said, “Evolution is a fact, not a theory.” And he was partly right; evolution is not a theory. He’s not right about evolution being a fact of course, unless he meant evolution in the most generic sense of change over time. We all agree that things change over time. But Sagan was clearly referring to a specific type of change: neo-Darwinian evolution. This is the idea that all life on earth is descended from a common microbial ancestor: that the information in our DNA is entirely the result of mutations over time that happened to convey survival advantage. It is this version of evolution that is neither a fact nor a theory.
What is a Theory?
Some creationists like to say, “evolution is just a theory” by which they mean it has not been proved. I would certainly agree that neo-Darwinian evolution has not been proved, and yet I would discourage creationists from saying, “evolution is just a theory.” Why? The problem pertains to the word ‘theory.’ The word can indeed mean an unproved assumption: conjecture. But this is not the most common definition. It is listed as 3b in the Merriam-Webster dictionary. ‘Theory’ can mean contemplation or speculation. But this is number 6 in the dictionary.com list of definitions. In other words, the use of the word ‘theory’ to mean “unproved, conjecture, or speculation” is legitimate, but is not the most common meaning of the word, and therefore can lead to misunderstanding.
What is the most common meaning of the word ‘theory?’ The first definition listed in dictionary.com is “a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena.” The listed example is: “Einstein’s theory of relativity.” This is the definition scientists generally have in mind when they speak of a theory. They are not referring to something that is mere conjecture or speculation. Rather, they refer to something that has been tested, has passed the test, makes accurate predictions, and therefore has supporting evidence.
The physics discovered by Einstein is great example of a scientific theory. It is hardly a mere assumption, conjecture, or speculation. It is well-tested. The theory of relativity makes very specific claims about the rates at which clocks tick, lengths contract, and masses increase as an object approaches the speed of light. There have been hundreds if not thousands of experiments which have tested these claims, and the claims of Einstein were correct in every case. Furthermore, no competing theory has been able to pass these tests. So, we have very good reasons to believe that Einstein’s theory of relativity is correct, or is at least a very good approximation of the way the universe behaves. It is well-supported by evidence.
Is Neo-Darwinian Evolution a Theory?
Is the idea of particles-to-people evolution a theory in this primary sense? Is it something that has been tested by the scientific method and passed? Does it make successful predictions for a class of phenomena? What kinds of tests and predictions qualify as supporting evidence?
Evolutionists often list three kinds of evidence that they believe supports evolution. First, organisms have certain similarities (and differences) in their anatomy. These similarities can be arranged into a hierarchy, which is what makes taxonomy possible (phylum, class, order, family, genus, species). Second, all organisms have basically the same genetic language. Furthermore, the DNA of two different organisms tends to be similar if those organisms are anatomically similar. Finally, the fossil record shows variations of organisms that no longer exist. Some of these are claimed to be transitional between organisms that do exist today, thereby apparently confirming that they are all related.
At least two of these lines of evidence are roughly consistent with neo-Darwinian evolution. The problem is this: they are also equally consistent with biblical creation. In order for evidence to support model A, it would have to not only be consistent with model A, but also contrary to the predictions of the alternative model B. If evidence is equally consistent with model B as with model A, then the evidence cannot be said to support model A over model B (or model B over model A). And indeed, the lines of evidence most often presented for evolution are perfectly consistent with biblical creation.
Consider the fact that organisms can be categorized into a taxonomic tree. But this doesn’t imply common ancestry. It is perfectly consistent with a God of order who made the universe to be at least partly understandable by human minds. Thus, creationists expect to find patterns in nature, including hierarchies. In fact, subatomic particles can also be arranged into a natural nested hierarchy – a taxonomic tree. Yet, no one claims that this is evidence that they are descended from a common ancestor! For example, tauons, muons, and electrons are all part of a common family of particles called “leptons” which have certain common properties. Leptons are part of a larger family called “fermions.” Other particles also fall into natural families. But does this mean that electrons have gradually evolved from muons over millions of years? Of course not.
Likewise, organisms share a common genetic language. But then again, all organisms have the same Creator. So that’s perfectly consistent with creation. Organisms that are closer together anatomically (and thus closer taxonomically) tend to have similar gene sequences. But that is what creationists would expect. Since DNA codes for traits, organisms with similar traits would be expected to have similar DNA. The nested hierarchy of genetic sequences is similar to the nested hierarchy of subatomic particles; yet no one claims that this is evidence that subatomic particles have gradually evolved from a common ancestor.
And regarding the fossil record, we do indeed find evidence of variations within kinds. We find different varieties of horse, some now extinct. We find different varieties of elephant, some of which are now extinct (such as mammoths). But this is a prediction of biblical creation; God created organisms with the ability to diversify within certain limits. Some of these variations have been lost over time. What we do not find in the fossil record is copious evidence of transitions between created kinds. There are always a handful of disputed specimens, but clear evidence of evolution between kinds is lacking. This is consistent with biblical creation, but is not consistent with new-Darwinian evolution.
In fact, can you think of any successful predictions of the evolution model that are contrary to the predictions of the creation model? Pretty much every example of supposed evidence for evolution is equally consistent with biblical creation: bacteria becoming resistant to antibiotics, commonalities in anatomy or genetics, “vestigial” structures, etc. These cannot be counted as evidence for evolution if they are equally evidence for creation.
What then is Evolution?
Hence, neo-Darwinian evolution does not have supporting evidence. As such, it is not a theory in the scientific sense of the word. In reality, it is merely a conjecture or speculation about the past. It is doubtful that evolution can even be called a hypothesis. A hypothesis has to be testable in principle. It must be falsifiable. For evolution to be a hypothesis, it would have to make predictions that are contrary to the predictions of biblical creation (not a straw-man misrepresentation of creation), and there would have to be some experiment that could either verify or falsify that prediction.
But most Darwinists do not treat evolution as a hypothesis. They treat it as an unquestionable presupposition; as a unifying philosophy through which all observations are interpreted. I don’t object to having presuppositions through which we interpret evidence; this is inescapable. But I would encourage Darwinists to think through the implications of their network of presuppositions, because it is inherently irrational. Namely, if neo-Darwinian evolution were true, there would be no basis for rationality or science, and hence no way to actually know that it (or anything else) is true. Neo-Darwinian evolution is inconsistent with the scientific method, as we have shown previously.
It is certainly the case that neo-Darwinian evolution has not been proved. But we probably shouldn’t say that it is “just a theory” because a theory (in the primary, scientific sense of the word) has supporting evidence, whereas neo-Darwinian evolution does not. When people say, “evolution is just a theory,” they probably mean it is unproved. But a scientist will be inclined to interpret the word “theory” in the scientific sense of something with supporting evidence – perhaps something that should be believed like the theory of relativity. But the theory of relativity is truly a theory in the scientific sense and thus has supporting evidence. Neo-Darwinian evolution does not. Therefore, it would be best to refer to evolution as a speculation or unsubstantiated conjecture about the past.
 From “The Cosmos” video series.
 Actually, there are some variations in the genetic language. A “stop” codon in one organism or part of an organism (like mitochondria) might translate to a particular amino acid in a different organism. But, these variations are small, and most codons are the same between them.