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Is Darwinian Evolution "Just a Theory"?

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Earlier I wrote here about the Scientific Dissent from Darwinism List, seeking to help students who have been misled into thinking there is no scientific disagreement over Darwinian theory. The list affirms that "Careful examination of the evidence for Darwinian theory should be encouraged." We often hear people who disagree with evolution saying that it's "just a theory." While that's not what the Dissent List signers say, we must ask: Are Darwin-skeptics using the correct terminology when they say Darwinian evolution is "just a theory"? Well, definitions are crucial: The answer depends on how you define "evolution" and how you define "theory."

In common usage, "theory" typically means a conjecture or a hunch. But scientists often use the word to refer to "a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, and tested hypotheses"1 or "a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence."2 Obviously those definitions suggest that a "theory" enjoys strong support from the evidence, and is much more than a mere hunch or conjecture. But if the scientific objections to Darwinian evolution that I discussed in my earlier article are valid, then under this stronger definition, it should not be called a "theory."

However, when scientists use the word "theory," they don't always mean a well-established idea that is supported by a broad range of evidence. Even in their professional writings, scientists sometimes use "theory" to refer to a conjecture or hypothesis that is not confirmed by the evidence. For example, here is a medical researcher writing in a scientific journal who used the word "theory" to refer to an idea that may or may not yet be established within science:

An old joke about the response to revolutionary new scientific theories states that there are three phases on the road to acceptance: 1. The theory is not true; 2. The theory is true, but it is unimportant; 3. The theory is true, and it is important -- but we knew it all along. ... Theory for scientists is like water for fish: the invisible medium in which they swim.3
Thus, even among scientists, the word "theory" can mean different things. Sometimes scientists use "theory" to refer to a new hypothesis that's untested and unverified. Other times scientists use "theory" to refer to a well-substantiated explanation that's strongly supported by the evidence. Because the term can have multiple, conflicting meanings, understanding what it refers to in a given context can be confusing. For that reason, to avoid confusion and ambiguity, if you want to express doubts about Darwinian evolution, it's better not to say that "evolution is just a theory."

If someone does use that formulation, however, we must also ask: What does "evolution" mean? As we saw in my previous post, no one doubts the idea that I called Evolution #1 -- that is, the uncontroversial observation that small-scale changes can occur in populations of organisms. Evolution #1, or microevolution, is well-supported by a large body of evidence. Evolution #2 refers to universal common descent, which receives wide support in the current scientific understanding. Whether that support is justified is another question that I leave aside for now. However, as the Scientific Dissent from Darwinism List shows, when it comes to what I termed Evolution #3 -- the idea that an unguided process of natural selection and random mutation can account for the complexity of life -- there is major scientific controversy and cause for doubt. It is when we speak about Darwinian evolution in this sense that the scientific evidence turns decidedly weak, as the mainstream technical literature confirms.

How, then, should we speak about "evolution" as a theory? Rather than using imprecise language, and saying things like "Evolution is just a theory," a better way to express legitimate doubts on the subject is simply to say, "The scientific evidence does not support Darwinian evolution."

References:

[1.] National Academy of Sciences, Science and Creationism: A view from the National Academy of Sciences, p. 2 (2nd ed., National Academy Press, 1999).
[2.] National Academy of Sciences, Science, Evolution, and Creationism, p. 11 (National Academy Press, 2008).
[3.] Bruce G. Charlton, "False, trivial, obvious: Why new and revolutionary theories are typically disrespected," Medical Hypotheses, Vol. 71:1-3 (2008).

Image: "B" notebook on Transmutation of Species, by Charles Darwin [Public domain or Public domain], via Wikimedia Commons.