Is Evolution “just a theory”, a scientific theory, or a fact?

There is a lot of misunderstanding when it comes to determining the status of evolution. We are all familiar with the lay, and often religion-motivated, misinterpretation of evolution being “just a theory”. This misrepresentation of the status of evolution is based on a confusion—a confusion which in many cases is deliberate—between the meaning of theory in the lay discourse versus scientific discourse. Another common area of misunderstanding is in addressing whether evolution is a scientific theory or a fact. Here’s the short answer: evolution is both a scientific theory and a fact.

I’m quickly going to comment on the irony of the “just a theory” argument. This argument gets its strength from the fact that many people do not know the difference between theory in lay discourse versus scientific discourse. Its power is based entirely on ignorance. As most of the people reading this blog probably already know, here’s the difference. A lay theory can be something that someone has just thought up; it can be deeply thought out or just pulled out of thin air. A scientific theory, on the other hand, is a carefully tested and evidentially supported means of explaining data. A theory is based on rigorous scientific testing of a hypothesis (which is the closest thing in science to a lay theory; though these hypotheses are generally more thoughtfully developed and evidentially-justified than most lay theories), intense peer review, and the constant possibility of disconfirmation.

The “just a theory” versus scientific theory is not the only area of misunderstanding. People, including many scientifically-oriented skeptics, frequently misappraise the status of evolution. Is it a theory or a fact? The answer is both. It is both because there are two dimensions to evolution: historicity and mechanism. Historically, evolution is a fact. The evidence for the idea that species evolved by way of gradual changes in population gene pools over time is so overwhelming that to not grant it the status of fact would simply be ludicrous. While it is true that we can’t truly know anything aside from each own personal existence, to the extent that we can we can know that other things we can know that evolution is a historic fact. The evidence from genetics, archaeology, comparative anatomy, embryology, and so forth preclude the possibility that a person can be knowledgeable of the relevant information, honest, rational and not believe in the factuality of evolution. These 4 factors simply cannot coincide. At least one of them has to be false.

The late eminent paleontologist Stephen J. Gould explains the issue as follows:

Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them. Einstein’s theory of gravitation replaced Newton’s, but apples did not suspend themselves in mid-air, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin’s proposed mechanism or by some other yet to be discovered.

The theoretical area of evolution is with regard to the mechanisms by which the historically factual process of evolution occurred. While we know for certain that evolution did occur because we have the data—the data are the facts, we use scientific theory to explain the data. That’s what scientific theories do: explain data. When it comes to explaining the data, not only is evolutionary theory a theory, it cannot become a fact. Theories explain data. Facts are data. So it’s not like we call natural selection a theory of evolution because we simply do not have enough evidence to call it a fact yet. We call it a theory because it explains the data. It will never be a fact. Indeed, if fact was a latter rung on the ladder (hypothesis–> theory –> fact) we would have been calling natural selection a fact for a long time by now. Natural selection is not the only scientific theory of evolution. There are others such as genetic drift and punctuated equilibrium theory. Natural selection, however, is the only process by which complex functionality can evolve.

11 Responses to “Is Evolution “just a theory”, a scientific theory, or a fact?”
  1. Koso says:

    You’ve got a pretty solid blog and see there’s a decent amount of activity on it, so I figure it’s worth commenting here.

    First off, just to clarify, evolution is NOT a fact, but you’re right, it is a theory and I agree with your definition of a theory (and good job differentiating between a “theory” in lay terms vs. a “theory” in scientific terms.).

    Wikipedia (as weak of a resource as it might be) has a good explanation. It is a fact that an apple has dropped from a tree towards towards the centre of the earth. Newton has since developed a theory called “gravity” that describes why this behaviour occurs. Although it is only called a “theory”, it is accepted in the scientific community and by lay people as near fact.

    And, yes, evolution is also a similarly founded fact.

    However, since I’m assuming that this argument might have likely stemmed from a “religion vs. science” or “evolution vs. creation” type debate, I’d like to also add that history, biology, and other types of science have also accepted the existence of Jesus and many other parts of the Bible as fact and “theory” doesn’t necessarily discount the other. I’m sincerely not trying to hijack this topic and switch the debate to religion vs. science, but I think that bit is still relevant and worth noting.

  2. ronbrown says:



    Can you clarify your position on evolution being or not being a fact? Early on you emphatically state that it isn’t a fact, then later you say that it is.

    Just to restate, though, evolution is a historical fact in the sense that given the amazing amount of evidence that it did occur (i.e., that populations did change over time), it would be ridiculous to not treat it as a fact.

    I’m not familiar with the existence of Jesus being viewed as fact by history or biology. Here’s the one credible source of info I have to the contrary: Christopher Hedges said it isn’t known whether or not Jesus existed. Christopher Hedges grew up in a Christian home. Moreover, he was the son of a Christian congregation leader. He also graduated from Harvard Divinity School. He has lived a life of thorough Christian experience and scholarship and is still a Christian, though he may well have shifted to being more of an agnostic cultural Christian. So if he says that there isn’t conclusive evidence (and I assume he means conclusive in the sense that it would be about as equal to believe that Jesus existed as, say, Socrates) I feel pretty comfortable taking his word for it. I just don’t see how he could comfortably make that statement otherwise. He’s as well-versed as anyone on the topic, and why on earth would he be motivated to lie or perhaps overstate agnosticism on this question?

  3. Koso says:

    I apologize for seeming unclear earlier with regards to evolution being a theory. Evolution is not a fact. As you explained, it is a fact that populations have changed over time. However, the idea of evolution or natural selection being the force that drove said changes is not a fact, but rather a scientific theory. My intended explanation earlier was to compare it to Newton’s theories of gravity. “Although it is only called a ‘theory’, it is accepted in the scientific community and by lay people as NEAR fact”. And evolution is also accepted as NEAR fact, however, it’s very nature prevents it from ever being anything other than a theory.

    As for the existence of Jesus, I’m really not sure how you can not accept it as fact. Do you even consider disregarding the existence of Napolean or Charlemagne as well? Or what about Julius Caesar? He is an even more ancient figure than Jesus and has less written about him? Surely if you can question the existence of Jesus, then these men have to be even higher up on your radar of fraud.

    As for your “credible source of info to the contrary”, I don’t follow it whatsoever. By your logic, I can prove that evolution is completely bogus if I can find an individual who was the son of a science teacher and graduated with a degree in science and yet still rejects the idea of evolution. First off, I guarantee that would be a relatively easy task for me. And secondly, I don’t think one person’s opinion, comment, or research on a matter has any true bearing… especially if there are countless other equally dignified people that strongly claim the opposite.

  4. JohnnieCanuck says:

    Koso, go back and read what he wrote, again. Facts are data. Theories explain data. Sometimes the same name gets used for a fact and a theory. Your inability to understand could be explained as deliberate, and religiously motivated.

    You use the word NEAR as if you mean to speak of the tentative nature of all theories. Newton’s theories of motion explained the data at hand. The data are still valid and his theories still explain them. The theory of Relativity, however, is able to explain Newtonian data and data gathered in high gravity or high speed situations. No-one knows when or if some new data will require modification of one of Einstein’s theories. Likewise the Theory of Evolution.

    As to your religious perspective, could you explain your statement, “history, biology, and other types of science have also accepted the existence of Jesus and many other parts of the Bible as fact”? Do you have specific examples you could give?

    Josephus is the only independent historical reference to a possible candidate for an actual Jesus. It is not only brief, but disputed. None of the newsworthy events attributed to his life appear in either Roman or Jewish accounts. All the rest of the words written about Jesus are non-contemporary, often by centuries.

    Modern biology contradicts almost everything the Bible has to say about living organisms. Bats aren’t birds, goats and cattle do not become striped by looking at striped rods while conceiving, etc. Neither of the mutually contradictory versions of creation in the Bible are supported by Biology.

    Other types of science have disproved things like the Shroud of Turin.

    Show us your evidence, or your extraordinary claims must be ignored. Just because the different Bibles state that the Bible is to be trusted does not make your Bible evidence for your claims.

  5. Alberto says:

    “Scientific theory” is a contradictory and ilogical phrase because nothing is scientific while it is not proven according to the scientific method; so, the theory of evolution is not real science but an esoteric speculation based on pantheistic pagan ideas. On the other hand, the remarkable intelligent designs of the universe and life is a rational and logical proof that a Creator really exists.

  6. Rachel says:

    Evolution can never become a fact simply because that’s not how science works: we cannot prove the null hypothesis. It is a theory that explains the facts (the data) very well but as you pointed out, Ron, there are other theories out there (and creationism is not one of them since it assumes that creationism is a fact a prior because that’s what God said). However, this does not mean that it could be dismissed as “just” a theory. If anything were to happen, it’s more likely that there would be an add-on to it, similar to Einstein’s upset of Newton’s physics. Newton’s theory is still very useful but not in all circumstances.

    As for Jesus being a factual historical figure: Unlike the other guys you mention Koso, there is no corroborating historical evidence for Jesus. There is, however, a lot of contradictory evidence in the Bible. For a great approach to this question, I highly recommend The God Movie. It showed very clear evidence that Jesus is a mythical figure.

  7. ronbrown says:


    From above:

    “Historically, evolution is a fact. The evidence for the idea that species evolved by way of gradual changes in population gene pools over time is so overwhelming that to not grant it the status of fact would simply be ludicrous. While it is true that we can’t truly know anything aside from each own personal existence, to the extent that we can we can know that other things we can know that evolution is a historic fact.”

    Some have commented if you’re going to call evolution a historical theory, you might as well call the existence of gravity a theory, too.

  8. Infinite Force says:

    I would like to add to this topic. Apart from documented religious concepts or any other religious concepts that hold the origin of species as a creation process by a desigher(s). There are two concepts when it comes to the origin of species. The first is the theory of evolution for the origin of species. The second concept is biological reproductive species as being fixed. I will agree with you that the theory of evolution is supported by tons of facts and also the fixed biological reproductive species as the origin of species. The difference is the theory of evolution premise is based on an assumption when it comes to the biological reproductive species term. This is the only species term that can be held as universal. Biological reproductive species term means a species that is able to reproduce fertile off-offspring. The premise of biological reproductive species as being fixed is observable and testable because humans can only reproduce with other humans and reproduce a fertile off-spring human. Humans are not able to biologically reproduce fertile off-spring with other biological reproductive species and this evidence concludes that humans are a fixed biological reproductive species. On the contrary, when it comes to biological reproductive species reproducing a new and fixed biological reproductive species which is what the theory of evolutution proposes over time, has never have been observed. Yes, the theory of evolution have other definitions for species and the term is based on similarity within different species. Because you see similarity which supports the assumtion of descent with modification the theory of evolution has tons of evidence ONLY supporting the UN-OBSERVED assumption that the origin of species arose thru this process. The same facts that evolution uses can be used by the fixed biolological reproductive species concept as common design. Just remember, the theory of evolution facts rests on an unobserved assumption with the biological reproductive species term.

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