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Is “Evolution” a “Theory” or “Fact” or Is This Just a Trivial Game of Semantics? (Part 3)

Casey Luskin

[Editor’s Note: This is a Part 3 of a 5 part series on whether evolution should be called a “theory” or a “fact.” See: Part 1, Part 2, Part 3, Part 4, Part 5. The full article can be found here.]

Darwinists claim that it is inappropriate to call “evolution a theory, not a fact” because a theory means “a well-substantiated scientific explanation of some aspect of the natural world.” In Part 1 and in Part 2, I discussed the fact that the word “theory” can have multiple meanings, ranging from a conjecture or guess (the soft definition) to “a well-substantiated scientific explanation of some aspect of the natural world” (the hard definition). In this installment, I will address the question, “Is it correct to call evolution a ‘fact’?”

A new article in Current Biology about Darwin Day celebrations quoted Johnjoe McFadden from the University of Surrey stating that “evolution is no longer just a theory. It is as much a fact as gravity or erosion. Scientists have measured evolutionary changes in scores of organisms.” The leading 20th century evolutionary biologist Ernst Mayr quite dogmatically (and wrongly) claimed that, “No educated person any longer questions the validity of the so-called theory of evolution, which we now know to be a simple fact.” Similarly, according to the ardently pro-Darwin U.S. National Academy of Sciences (NAS), evolution is a “fact”:

Is Evolution a Theory or a Fact? It is both. But that answer requires looking more deeply at the meanings of the words “theory” and “fact.”

(U.S. National Academy of Sciences, Science, Evolution, and Creationism, pg. 11 (National Academy Press, 2008).)

What these Darwinist authors miss is that the legitimacy of calling evolution a “fact” depends on the meaning of the word “evolution.”

The debate over evolution can be confusing because equivocation has crept into the discussion. Some people use evolution to refer to something as simple as small changes in the sizes of birds’ beaks. Others use the same word to mean something much more far-reaching. Used the first way, the term “evolution” isn’t controversial at all; used the latter way, it’s hotly debated. Used equivocally, evolution is too imprecise to be useful in a scientific discussion. Darwin’s theory is not a single idea. Instead, it is made up of several related ideas, each supported by specific arguments:***

  • Evolution #1: First, evolution can mean that the life forms we see today are different than the life forms that existed in the distant past. Evolution as “change over time” can also refer to minor changes in features of individual species — changes which take place over a short amount of time. We can observe this type of evolution going on in the present and even skeptics of Darwin’s theory agree that this type of “change over time” takes place. Evolution in this sense is “fact.” However, it is invariably the case that when Darwinists cite some present-day observations of change within a species, they will be small-scale changes that are not easily extrapolated to explain how complex biological features arose.
  • Evolution #2: Some scientists associate the word “evolution” with the idea that all the organisms we see today are descended from a single common ancestor somewhere in the distant past. This claim became known as the Theory of Universal Common Descent. This theory paints a picture of the history of life on earth as one great branching tree. While this meaning of evolution is not necessarily incompatible with intelligent design, there are many scientific skeptics of evolution who are skeptical of Universal Common Descent.
  • Evolution #3: Finally, some people use the term “evolution” to refer to a cause or mechanism of change, the biological process Darwin thought was responsible for the branching pattern. Darwin argued that unguided natural selection had the power to produce fundamentally new forms of life. Together, the ideas of Universal Common Descent and natural selection form the core of Darwinian evolutionary theory. “Neo-Darwinian” evolution combines our knowledge of DNA and genetics to claim that random mutations in DNA provide the variation upon which natural selection acts in a completely unguided fashion. It is this form of evolution that is the most controversial meaning of evolution.

So is evolution a fact? If by “evolution” one simply means “evolution #1,” i.e. small-scale change over time within a species, then evolution is indeed a fact. No one disputes this kind of “evolution.” Thus when Johnjoe McFadden states that “[s]cientists have measured evolutionary changes in scores of organisms” and therefore evolution “is as much a fact as gravity or erosion,” he is stating the obvious because he is simply referring to evolution #1.

But Dr. McFadden is pulling a bait-and-switch: he is using relatively trivial examples of evolution #1 to bolster more controversial definitions of “evolution.” Thus if by “evolution” one means universal common descent (evolution #2), or neo-Darwinian evolution (evolution #3), where the primary adaptive force building the complexity of life is unguided natural selection acting upon random mutations, then many scientists would argue that such “evolution” most certainly is not a fact.

A Final Look at the NAS’ Mistake
Finally, consider how the NAS defines evolution as a fact:

In science, a “fact” typically refers to an observation, measurement, or other form of evidence that can be expected to occur the same way under similar circumstances. However, scientists also use the term “fact” to refer to a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it or looking for additional examples. In that respect, the past and continuing occurrence of evolution is a scientific fact. Because the evidence supporting it is so strong, scientists no longer question whether biological evolution has occurred and is continuing to occur. Instead, they investigate the mechanisms of evolution, how rapidly evolution can take place, and related questions.

(U.S. National Academy of Sciences, Science, Evolution, and Creationism, pg. 11 (National Academy Press, 2008).)

I won’t dispute the NAS’s definition of fact, but it’s clear that unless by “evolution” they mean evolution #1, then there are many scientists who will disagree with their claim that evolution is a fact. However, the NAS DID define evolution as evolution #3, i.e. being driven by natural selection acting upon mutation-caused variation:

In the century and a half since Darwin, scientists have uncovered exquisite details about many of the mechanisms that underlie biological variation, inheritance, and natural selection, and they have shown how these mechanisms lead to biological change over time. Because of this immense body of evidence, scientists treat the occurrence of evolution as one of the most securely established of scientific facts. … The atomic structure of matter, the genetic basis of heredity, the circulation of blood, gravitation and planetary motion, and the process of biological evolution by natural selection are just a few examples of a very large number of scientific explanations that have been overwhelmingly substantiated.

(U.S. National Academy of Sciences, Science, Evolution, and Creationism, pg. xiii, 12 (National Academy Press, 2008).)

The NAS is wrong. Since the NAS defines “evolution” as full-blown neo-Darwinian evolution, there are many scientists who will not agree that it is a fact.

***Some parts of this post were adapted from the textbook Explore Evolution: The Arguments For and Against Neo-Darwinism.


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.