Evolution: theory, fact, or both?

December 1, 2015 • 10:00 am

I’ve long been uncomfortable with explaining, in public lectures, why evolution is both a theory and a fact. To do that properly, you have to explain what a scientists really mean by the word “theory” and why it’s not just an idle guess or speculation. But that can be confusing, because I always say that a “theory” is an explanatory schema that makes sense of a body of facts, a sort of organizing principle for thinking about things that happens to explain all the data. But I’ve never been comfortable with that, as even guesses can make sense of a body of facts, but have not been tested nearly as rigorously as the theory of evolution. “String theory,” for example, makes sense of some things, but nobody knows whether it’s the correct explanation for particles. I always have the feeling that I’m confusing my audience when I explain why evolution is a theory, and then go on to show that what I see as the five pillars of evolution—evolutionary change, relatively gradualistic change of populations (i.e., change over many generations rather than a few), natural selection as the process producing “design” in nature, common descent, and speciation—are actually facts. 

In his famous essay “Evolution as fact and theory“, Steve Gould also made this distinction (my emphasis):

Well, 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 apelike ancestors whether they did so by Darwin’s proposed mechanism or by some other, yet to be discovered.

Moreover, “fact” does not mean “absolute certainty.” The final proofs of logic and mathematics flow deductively from stated premises and achieve certainty only because they are not about the empirical world. Evolutionists make no claim for perpetual truth, though creationists often do (and then attack us for a style of argument that they themselves favor). In science, “fact” can only mean “confirmed to such a degree that it would be perverse to withhold provisional assent.” I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms.

. . . Evolutionists have been clear about this distinction between fact and theory from the very beginning, if only because we have always acknowledged how far we are from completely understanding the mechanisms (theory) by which evolution (fact) occurred.

While I don’t have a big beef with this passage, which is of course very famous, it’s also confusing. If you claim that the “mechanism” for evolutionary change that produces design-like features of organisms is natural selection, is that claim a theory or a fact? It’s not only a theory, for we have enough evidence for it—and no credible alternative theory—that we can take it as provisional truth (i.e., fact). So is there a real difference, as Gould claims, between the “idea” of natural selection (Gould’s “theory”) and the observations that it works in nature, has a sound theoretical basis, and has no other explanation when referring to adaptations (Gould’s “fact”)? Is the notion that lineages split by a process of speciation that renders them unable to exchange genes (a process), a “theory,” as Gould would have it, or a fact? I see it as a fact, and so the distinction between theory and fact that, claims Gould, all biologists accept, is nebulous.

At one point, when Darwin gestated and then birthed the theory encompassing my five points, that theory had not yet attained the status of Facthood, for there simply weren’t enough data on, say, speciation or natural selection in the wild to say that Evolution was a Fact. But over the last 150 years, Facthood has been attained.

I was thus pleased to see that Richard Dawkins has taken a break from tweeting to write a good popular analysis on his organization’s website of the confusing distinction between evolution as theory and fact: “Is it a theory? Is it a law? No, it’s a fact.” In that essay, which is well worth reading, Dawkins encapsulates the ambiguity and confusion many of us feel while teaching evolution, and resolves it in a simple way: stop arguing that evolution is a theory, and emphasize instead that it’s a fact. (It is, of course, both, but it confuses people to dwell on the “theory” claim unless you’re debating someone who argues that “evolution is only a theory.”):

The party line among scientists arguing for evolution is to promote Sense 1 [the way I define theory above, as opposed to “Sense 2,” the popular notion of a theory as an idle guess or speculation], and I have followed it until today. But now I want to depart from the party line. I now think that trying to clear up this terminological point about the meaning of “theory” is a losing battle. We should stop using “theory” altogether for the case of evolution and insist, instead, that evolution is a fact.

. . . We are failing to get across “Theory, Sense 1”. Let’s dump it and talk frankly of evolution as a fact, from which it would be perverse to hold assent.

The notion of “fact” that Dawkins uses above also comes of course from Gould’s essay, as shown above. And I think that’s a good definition of scientific fact, with the caveat that “withholding assent” refers to those people who are qualified to judge scientific evidence. (If you don’t use that caveat, then more than 70% of Americans do not give their assent to a purely naturalistic theory of evolution.)

What remains a theory—or even a hypothesis—is the claim that most of evolutionary change is driven by natural selection. As I said above, I think we have enough evidence that what Dan Dennett calls the “designoid” features of organisms—the spines of the cactus, the cryptic coloration of a flatfish, the insect-entrapping shape of a bucket orchid, the fusiform shape of dolphins, and so on—result from natural selection. But we don’t know what proportion of all evolutionary change (and that’s itself ambiguous: do we mean changes in characters, or changes in genes?) is due to selection versus other evolutionary forces like genetic drift. One can make a good case, for instance, that among all alterations in the genome of a lineage, most of the DNA changes are due to drift rather than selection. So I’m happy, with the proper caveats, to regard as a hypothesis the statement that “most of the change in an organism is due to natural selection,” while accepting as a theory (or fact) the statement “nearly all the ‘designoid’ features of organisms are due to natural selection.” This is, of course, also confusing to non-biologists, and so I agree with Richard when he says this:

In our tussles with creationists it is evolution itself rather than natural selection that bears the brunt of their attacks. So we can set aside the status of natural selection and concentrate on the fact of evolution as something so firmly established by evidence that to deny it would be perverse. It is a fact, beyond all reasonable dispute, that if you trace your ancestry and your dog’s ancestry backwards you’ll eventually hit a common ancestor. It is a fact, beyond reasonable dispute, that when you eat fish and chips you are eating distant cousin fish and even more distant cousin potato.

So I’m happy to simply avoid explaining why evolution is both a theory and a fact, and in future lectures will say it’s both, but not go on to the confusing discussion of “theory” unless someone asks in the Q&A. I’d prefer, as this is what I lecture on anyway when giving the evidence for evolution, to claim that the important idea is that evolution (at least the five tenets I give above), is a FACT. And of course in my talks to the public I do mention natural selection and the evidence supporting its pervasiveness.

Richard winds up by arguing that evolution is not a “law,” and again I fully agree with him. But that’s a minor issue, for few evolutionists would even use the word “law,” which to us means something like the “laws” of physics: regularities that are never violated. Evolution is not a law in this sense, for there are virtually no statements you can make about the process that hold across all 3.8 billion years of evolution. The only one I can think of is that “all lineages evolve genetically,” for I don’t think there were or are any exceptions to that. But all other generalizations about evolution are subject to qualifications and exceptions.

69 thoughts on “Evolution: theory, fact, or both?

  1. Evolution is like gravity. It is a theory, but it is also a fact. Evolution, like gravity, is real and readily verified.

    1. I think a better way of viewing it is as an outcome. If you’ve got imperfect replicators, where the amount of replication is at least partially influenced by their environment (including other replicators), then the result is evolution. Sort of like the statement: if you’ve got money in the bank, and it gains compounded interest (ignoring fees etc. for the moment), then the result is exponential growth of your money over time. Neither evolution nor exponential money growth is ‘law,’ in the sense that it must be obeyed everywhere under every circumstance, rather it is the consequence of the facts of the situation you’re considering.

      1. I think that is a good point worth noting. Theory or fact can be irrelevant with regard to use, function, and outcome.

        A member of ISIS can use a cell phone to report to his comrades and not have an iota of knowledge about the physical laws required to make such events possible.

        This, in my view, is a major burden for secularists to show the incompatibility between science and religion, because you do not need to know anything about science to be a participant in the world or blow it up with pirated WMDs.

    2. Evolution and Gravity are facts. “Evolution by Natural Selection” and “Gravity by Curvature of Space-Time” are theories. We need to stop saying “Evolution” is a theory, it isn’t.

      I have no idea why this is so hard.

  2. Facts are the world’s data. Theories … explain and interpret facts… humans evolved from apelike ancestors whether they did so by Darwin’s proposed mechanism or by some other, yet to be discovered.

    I don’t think you can call that a fact by this reasoning. Humans evolving from apelike ancestors is not an observation – data – but a theory to explain observed similarities.

    1. I get what you are saying, but I think what he was getting at is that there is a fossil record that shows the virtual transformation of apelike species –> humans. The fossils and their succession of ages are regardable as hard facts. That this means that these earlier species evolved into those later species is a very strong and direct inference, and we call that strong and direct inference a fact. I get that there is a bit of sleight of hand there.

      1. “The fossils and their succession of ages are regardable as hard facts.”

        But all dating mechanisms rely on a whole load of theory. There is no way of neatly distinguishing between “facts” and “theory”.

        1. I think we can distinguish, though a lot of statements typically claimed to be facts are a combination of fact and theory. IMO at bare bones the facts are:

          1. When we dig we find skeletons that change with layer.
          2. We observe patterns of phenotypic similarity between organisms, both skeletons in the ground and living/better preserved organisms.
          3. When we watch volcanic and other soil deposition processes, the new stuff gets deposited on top of the old stuff.
          4. Radioactive decay is largely uninfluenced by chemical environment and observed in most cases to be exponential in form.
          5. Living organisms replicate…almost always imperfectly.
          6. The genetic component of replication is DNA.
          7. Analyzing genetic codes, we observe patterns of genetic similarity between organisms.
          8. Environment influences how much an individual living organism can and does replicate.

          We also have a couple of ‘facts about facts’:

          9. Facts #3 and #4 are mostly consistent; i.e. radioisotpic analysis confirms that layering is mostly old layers on bottom, newer layers on top.
          9. Facts #1, #2, and #7 are also mostly consistent: we find the patterns of similarity from genetic and phenotypic analysis confirm each other.

          From these statements facts you can use some pretty simple frameworks to build up the ‘theory’ of evolution. In broad outlines its not really intellectually difficult; Darwin’s idea was really a head-slapper from the ‘why didn’t we think of this earlier’ department.

          1. … a lot of statements typically claimed to be facts are a combination of fact and theory.

            Absolutely everything claimed as a “fact” is also a “theory”! These cannot be distinguished.

            Take your first sentence. Even concepts such as “skeleton” and “layer” are *interpretations* of what we see and are thus entwined with theory.

      2. It is important to consider not just the fossil sequence but also the independent genetic sequencing evidence, and the independent karyotype evidence. It is the convergence of all these independent lines of evidence that makes the hypthesis of common descent a fact.

    2. It’s certainly a fact that we evolved from apelike ancestors, as tons of evidence, including genetic data testifies that. It would be perverse to withhold assent from that claim, so it’s a fact

      1. Why not the law of evolution? Change over time as a result of natural selection is how nature works. Therefore it should be a law! This would cause creationists to scratch their heads because of the power of the word law. The way scientists view theory (the correct way) vs. the average person (the incorrect way)is not the same. Theories are powerful constructs to describe observable phenonmena and they are supported by evidence, as well as being scrutinized, critiqued, tested, modified and able to predict future observations (a la evolution with genetics)

        1. Living systems are those showing an organised metabolic activity oriented towards growth and self-replication (inheritance).
          Such replication is inevitably slightly imperfect, generating heritable variation. Some of this heritable variation will inevitably impact replication rate, whether directly or indirectly. Therefore the process of selection is one inevitably impacting living systems.

          Or if you don’t like that argument from first principles, let’s do empiricism, and observe that all the components of Darwin’s Engine: variation, some affecting replication rate; heritability of variation; resource limitation; all represent testable, and much-tested, assertions about the material world— about real organisms so far known. Therefore the Process of Selection, far from being empirically empty, or tautologous, defined by its premises is, so far as observations have yet shown, an inevitability.

          All sounds to me like selection and change of things we call alive is a natural law.

  3. This makes sense to me. (Since I was never taught evolution I’ve had to learn it on my own, and I’m still working to improve my understanding. As a former religionist, I still hear all the old arguments in my head, and realize my “answers” are still a bit clumsy.) Concentrating on evolution as THE fact (rather than natural selection) really simplifies the concept. I get it!

  4. Here is some additional support from a publication by the National Academy of Sciences:

    “[T]he evidence supporting descent with modification, as Charles Darwin termed it, is both overwhelming and compelling. 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. Biologists also are confident in their understanding of how evolution occurs.”

    “[T]he past and continuing occurrence of evolution is a scientific fact. [Emphasis supplied.] Because the evidence supporting it is so strong, scientists no longer question whether biological evolution has occurred and is continuing to occur.”

    -”Science, Evolution and Creationism,” National Academy of Sciences (2008)

    My take on what Jerry has written is that we are actually talking about two different “facts”: (1) the consistently observed fact that the process of evolution is occurring; and (2) the fact that natural selection is the primary driver of the process of evolution, which has been well-established through a number of fields of scientific inquiry since Darwin first proposed that idea.

  5. I’d say something like:

    (1) “Theories” are explanations.

    (2) Evolution is an explanation that has been proven true by overwhelming evidence.

    (3) That makes evolution a fact.

  6. To me, the facts are the experimental, or empirical, data gathered in the field or in the lab. The theory is an intellectual construction which integrates and thereby explains those facts. It may be true, a “fact” also, but it is still an intellectual construction. In that sense, to me at least, evolution is a theory like quantum mechanics or plate tectonics (both “proven” or, at least, accepted as facts in the sense that the contrary is extraordinarily unlikely) or string theory (which is not proven at all, may never be or — according to many — false).

    Don’t know if this helps in battles with the opposition.

  7. The effort to decide what to call evolution by natural selection reminds me of efforts to clearly distinguish “science” from “non-science”. Was alchemy an early science or a pseudoscience or not science at all? How about psychoanalysis? And when you ask such questions you immediately fall into a debate over the necessary and complete criteria for “science”. This inevitably ends up being a bit of a mess since science rarely proceeds in a textbook fashion, and “science” was never a formal process with explicit rules anyway. The same is true for scientific theories, hypothesis, laws, and “facts”. These are not really terms of art, they are just phrases that scientists use when they describe various bodies of work.

    Engaging these meta-arguments just plays into the hands of lawyerly opponents out to score points with an audience but uninterested in what is true. In general, I think it’s a waste of time to even engage these meta-arguments at all. “Was alchemy science?” is not nearly as fruitful a discussion to have as “Was alchemy correct?” Similarly, if someone asks whether evolution is a theory or a fact, I think it is better to just say, “Here is why I think it is true”, and direct the discussion there because nothing useful is going to come out of the theory/fact discussion. Evidence of the uselessness of the theory/fact discussion is that, among themselves, scientists NEVER raise that question. Not ever. It’s just not the right question.

  8. A minor quibble.

    … few evolutionists would even use the word “law,” which to us means something like the “laws” of physics: regularities that are never violated.

    To a physicist “law” does not quite mean “never violated”. For example, Newton’s law of gravity is very useful but does not work as well in strong gravitational fields.

    The difference between a “law” and a “theory” is really that a law can be stated in one sentence or one equation, whereas a “theory” is more complex than that.

  9. The fact is what’s true. The theory (or whatever you prefer to call it) explains why.

    Fact of gravity: things fall down.
    Further fact (Galileo): moons orbit other planets, not just Earth.
    Further fact: all objects appear to exert an attractive force on one another.

    Theories of gravity:
    1. (Aristotle): All things are drawn towards the Earth’s center. This is FALSE.

    2. (Newton): F = g*M1*M2/r*r. This is also FALSE but it’s an extraordinarily good approximation.

    3. (Einstein): General Relativity. This is the best yet. For all practical purposes it works. But it’s a classical (i.e. non-quantum) theory so it must also be FALSE.

    Fact of evolution: All living things have descended from a common ancestor. The process by which this happened, change of alleles within populations, continues.

    Theories of evolution:
    1. (Lamarck): Acquired traits are inherited. This is FALSE.

    2. (Darwin): Natural Selection. This is TRUE but INCOMPLETE.

    3. (Modern Synthesis): Natural selection, neutral selection, genetic drift, geographical isolation, horizontal gene transfer all contribute to evolution. This is pretty damn good. Is it the whole story?

    1. A better description of GR is that it is incomplete or possibly incompatible with QM. Or maybe GR is inadequate to predict QM, but FALSE seems not applicable.

      1. Agreed. There is no reason for saying GR or QM is false. That they are incompatible means there is a problem, but which one is at fault? Most theories, sorry, hypotheses which try to reconcile the two, such as string theory or quantum gravity, posit additional dimensions to spacetime. Gravity’s extensions to these spaces is then viewed by us in 4-d spaces as the equivalent of the other 3 forces of physics. If that is true, then GR is right, but insufficient. In the end, we don’t know where the problem is, only that there is one.

    2. Your distinction between “fact and “theory” doesn’t work since all “facts” are theory laden.

      E.g.: “Fact of evolution: All living things have descended from a common ancestor.”

      Once can equally say that common descent is an explanation of what we observe, so is on the “theory” side of your divide.

  10. My view is that biological evolution, that species evolve, changes in allele frequencies within populations over time, is an observed fact. For any reasonable meaning of the word fact, such as Gould described.

    And that the Theory of Evolution, The Modern TOE, The Modern Synthesis, is the theory that explains all that we have discovered about the observed phenomenon of biological evolution.

    I think there may be a distinction between facts and theories worth maintaining. Natural Selection and Speciation are parts of the theory of evolution. I agree that they are also observed facts now. But it seems to me that just as with the more general case of evolution there are the factual phenomena that can be observed and we have devised (sub)theories to explain them.

    I would say that while theories include many facts that they also include several other things, like concepts and models. These other things relate the facts, generally and to each other, and allow us to explain how things did or will happen. They allow us to discover things that were not previously known, or that where known but not understood to be related to the phenomenon the theory was originally designed to explain.

  11. Scientists always get in trouble when they decide it would be a bad idea to admit what they really do, and instead cook up a story for public consumption and then try to defend it. The reality is that scientists use words like “theory,” “model,” “law,” “hypothesis,” in completely inconsistent and unsystematic ways. And that’s okay!


    And most scientists don’t talk about “facts” at all, when they’re actually doing science.


    They’re happy to talk about ideas being “correct” or “true” or “right.” I’m in favor of just being honest in public about what we mean when we use these words.

    1. A very good point. The word ‘fact’ is not often used by scientists, and that is probably a good thing. And furthermore…
      ‘Why Evolution is a Fact’ sounds a lot more clunky than ‘Why Evolution is True’.

    2. … the hierarchy of “hypotheses” and “theories” and “laws” and “facts” that many people are taught in elementary school (or wherever)…

      I don’t recall being taught that at all, all the way up to doing my Ph.D. in theoretical physics.

      Was this an egregious failing among my educators or were they all pragmatists? 😉



      1. Ditto. At it’s core I think the best science is exceedingly pragmatic, and so very few productive scientists give these terms even a passing bit of attention. It’s only when scientists have to wade out into a skeptical world that doesn’t understand science that these terms come up as something to worry over.

        The public’s desire to declare various ideas “fact”, “theories”, “wild guess”, betrays in my mind a slightly authoritarian bent, as though what is true is not what you’ve been personally convinced is true, but what has been branded as true by the proper authorities.

    3. “Is evolution ‘just a theory’? A “theory” in science is a structure of related ideas that explains one or more natural phenomena and is supported by observations from the natural world; it is not something less than a “fact.” Theories actually occupy the highest, not the lowest, rank among scientific ideas. … Evolution is a “theory” in the same way that the idea that matter is made of atoms is a theory.”

      This is actually a definition of a theory that scientists say when they’re talking about evolution. However, it can’t be the one used by scientists where they’re refering to String Theory. As I understand, String theory could explain one more natural phenomena, but has not yet been supported by observations from the natural word.

      Thus,it looks like that scientists themselves have two different and inconsistent definition of what a theory is.

      1. Thus,it looks like that scientists themselves have two different and inconsistent definition of what a theory is.

        More than two I expect. Scientists use the word “theory” very loosely. “Theory” is not a term of art of science. All the definitions scientists sometimes give to explain what they mean when they use the word are descriptive, after-the-fact, rather than prescriptive. Actual scientists spend zero percent of their working time discussing what is and isn’t a theory. This is entirely a discussion that comes from the outside of science, when people put scientists on the spot and say, “When you say this is a theory, do you mean it isn’t proven?”. Scientists don’t normally think of things as proven or not proven either, so this whole line of thought is alien to how scientists operate in practice.

        In practice, Crick and Watson publish their inference of the structure of DNA. It makes sense to the readers of the article. It explains a number of salient facts about DNA and inheritance. So, provisionally, people who read this paper and think it’s a good explanation set about performing experiments *as if* it is correct. Insofar as those experiments work, they keep going. They keep going for decades, in fact. No one ever stops to really ask, “Is the double-hellx structure proven? Is it a fact?” Other people perform experiments that replicate the data Crick and Watson present. They perform related experiments that produce related results. The perform experiments that reveal other notions, coiling and super-coiling, say, the mechanisms for copying, etc. On and on it goes. It’s actually quite Darwinian… the ideas about DNA structure that don’t work, that don’t provide ideas for new experiments, or provide ideas that don’t pan out, die quiet deaths… are simply forgotten. No one declares them false. The ideas that do work get used over and over in more and more experiments. After a while it becomes perverse to deny something like the structure of DNA, the evidence has piled so high. But there simply is no formal, or even semi-formal stage where things get labeled as “facts” or “theories”, any more than there is an “official” first turtle that isn’t a reptile.

    4. Quite true on the practical ambiguity of working scientists, though you must always remember how the apologetic methodology of antievolutionism inevitably hitchhikes on all nuance via their addiction to authority quoting.

      The biggest thing to remember regarding the fact vs theory dichotomy in the antievolution context is that while the regular science grapples with which theoretical frames best accommodates the most evidential facts, and how further to spur the generation of new evidence to assess, antievolutionists never actually get to the evidential fact explaining stage in their own context.

      Their lapses can be summed up in several key nodes: (1) their pathologically common over-reliance on secondary citation (only 5% of antievolutionist authors even bother with primary source documentation, and those glance by at best 10% of relevant technical work), (2) their inability to conceptualize speciation playing out over Deep Time (this applies equally to YEC & ID authors, so is not a geochronology snag per se), and (3) never laying out in their own heads what intermediate fossils or biological systems would look like (meaning whatever is presented to them will be sloughed off as never good enough). There are literally no counterexamples I know of for that #3, from St. George Mivart in 1870s down to Casey Luskin blathering currently over in ID land.

      I’ve been exploring the antievolutionist mindset and methodology in #TIP project at http://www.tortucan.wordpress.com, currently cataloguing some 1900 antievolutionist authors, along with the science dataset context of some 23,000 resources.

      All the postings at #TIP are open access (Richard Lenski liked my TIP 1.3 piece surveying all current antievolutionists mangling of the Punctuated Equilibrium topic, showing how they don’t discuss the subject even when they bring it up themselves).

  12. “The word ‘fact’ is always likely to make biologists tremble in their boots, as there are so many exceptions to every rule.”

    Nick Lane in Life Ascending 🙂

    I like to think of “the facts” as a starting point on which everyone who matters agrees, so we can get started on the important issue of choosing between alternatve explanations (theories).

  13. “…then more than 70% of Americans do not give their assent to a purely naturalistic theory of evolution”

    But they are perverse not to do so.

    1. “But they are perverse not to do so”
      The argument of the non-literalists is to admit evolution but insist that God needed to guide evolution toward humans. Well, that’s like claiming God needs to guide water downstream to the sea. If you have a natural explanation, like natural selection, interjecting God’s hand is useless and a non sequitur. That’s a perversion of logic.

  14. Very good, and i will have to trot over to Dawkins’ web site and look at his essay.
    For my evolution class one of my reading assignments is Goulds’ Evolution as Fact & Theory essay. I use study guide questions to help them navigate through it and procure the main points because, man, the guy was great but he could be rather convoluted at times.
    To me, the main points of his were that evolution is a fact b/c we see it happening now and we see it had happened in the fossil record. Evolution is a fact because of these observations. The main ‘theory’ part of evolution is the mechanism(s) by which it works in the instances where we have not directly observed its mechanisms. We did not observe, for example, how the leopard got its spots but we can infer it was from natural selection.

  15. When teaching I always use an analogy to the law. In a court of law the lawyers present evidence that becomes the facts of the case. This includes conclusion, such as the conclusion that a murder has been committed. The true facts might include a bullet-ridden body shot from a distance and no sign of a weapon but a pile of shell casings 10 meters away. If both sides in a case accept the conclusion that the person was murdered, this conclusion then becomes a fact in the case.

    If this case is appealed, the appeal court generally accepts the facts of the lower court and focuses on legal issues or those conclusions that are in dispute (e.g., that the accused was in fact the murderer).

    So, the five pillars of evidence are the most basic facts in the case, and the conclusion that life has evolved is a conclusion that is so widely accepted as true that it is also considered to be a fact.

    I guess in the future I will add that the evidence for evolution being the result of a conspiracy between natural selection, sexual selection, genetic drift, and the founder effect is so strong that this, too, is a fact. The only question is the relative importance of these processes in carrying out evolution.

  16. “Fact” gets used various different ways which is confusing sometimes.

    The “non-linguistic” use is simply “what is the case”. What one should call “fact statements” are purported statements *about* what is the case. So “Biopopulations change allele frequencies over time.” is such a factual statement. It also happens to be a (more or less) true one, as far as we can tell. Both what I just called “fact statements” and “true fact statements” are sometimes also called “facts”. Bertrand Russell, most notably, sometimes equivocates between the various uses.

    A *theory* in pure mathematics, theoretical physics (sometimes) and logic is a set (usually) of statements (or propositions) closed under a consequence relation of some kind. So in this sense there are many theories of evolution, some with truer fact statements than others. In other contexts, “theory” is also used to mean single statements or propositions, which are better called “axioms” or “theorems” depending on their status (which is a matter of organization) in the theory.

  17. Another problem with the word theory is that there are many variants of evolution theory. there are folks who emphasize natural selection and folks who think neutral mutations are the dominant mode of change.

    The only “theory” that seems common to all biologists is that mutations in the germ line happen, and some alleles become dominant over time.

  18. “In our tussles with creationists it is evolution itself rather than natural selection that bears the brunt of their attacks. So we can set aside the status of natural selection…”

    I think Dawkins may be making a mistake to adjust his terminology to reach the lowest level of religious evolution-opponents. Better to address the more sophisticated ID opponents of naturalistic evolution, and hope for a trickle-down effect. Among IDers it is precisely the role of natural selection that is under debate.

    Winning an argument with fundamentalist creationists often just pushes them to a higher level of denial, ID. If we want to make real progress, we need to address the adequacy of natural selection.

  19. There’s one thing I don’t get about the “natural selection vs. genetic drift” thing: Can changes by genetic drift accumulate at all? If the drift drifts too far, the changes become visible to natural selection, so why don’t you get just minor fluctuations around the point of zero effect?

    1. Visualize an infinite plane of zero effect, instead of a point, for starters. The space of selection neutral mutations is very large, so one could drift off in many directions for a very long time without encountering significant selective pressure.

    2. Actually the need to be “neutral” implies negative or purifying selection. (Of course, Larry Moran would argue that 90 percent of the genome can mutate to its heart’s content, because it doesn’t do anything and can’t be detrimental.)

      But neutral mutations of functional sequences are also possible, or we wouldn’t have any genetic diversity.

      The Lenski experiment demonstrates that neutral mutations can accumulate and enable beneficial gain of function mutations.

      1. Importantly too, even slightly negative mutations can become fixed, especially in small populations. This is just a fact of sampling.

  20. Oy.

    Well, the first observation I can make is that T. Ryan Gregory nearly emptied out the phase space of biology 2007: “Evolution as fact, theory, and path. … Evolution as path deals with the factual details of life’s history”. [ http://link.springer.com/article/10.1007%2Fs12052-007-0001-z ]

    I could add back that Richard is wrong, it is very likely that evolution is a universal law. When you try other processes as modeling organisms they are outcompeted by evolutionary populations. E.g. lamarckism (epigenetics), stasis, …

    But that last addition is semantic, as is most of these concepts. “Theory” – which should be defended for its use within science – has other connotations in theoretical physics and mathematics than Richard accounts for. String theory started out as an plausible theory within theoretical physics because it passed the test to produce particle state. It has later been tested on other stuff like producing the correct black hole entropy, but has not yet predicted and been tested on something unique, making it unclear if its only use is as a useful mathematical theory for physicists.

    Stepping back from the semantics and education wars, I would try to rely on quantitative, testable descriptions of science. I have found that in measurement theory.

    Measurement theory has no meaningful, testable difference between observation, hypothesis of theory – they can all be described by statistics of confidence intervals. And a fact is simply a robust case of any of them, meaning it may be reversible in 1 case out of 20. Now, as Sean Carroll interestingly observed, modern science has for some reason converged on (near) absolute fact. As Jerry likes to note, a water molecule is 2 atoms of hydrogen bound to 1 atom of oxygen, and it has been such for 14 billion years.

    Nitpick: Gould was wrong too. Theories do not “go away” because better ones are found. We still use Newton’s gravity in some 99 % of cases, including interplanetary travel, because it is simpler and correct enough. And that is a fact.

  21. In my environment I use ‘theory’, like ‘the germ theory of infectious diseases’. A theory is stronger than a fact. A fact can be ‘un-facted’ by a new observation or experiment, a theory cannot be undone so easily, since based on so many facts.
    I also like Daniel Dennet’s take: evolution as an algorithm: If there is reproduction, variation, heredity and limited resources, evolution is *inevitable*.

      1. Do not curse the algorithm. The algorithm is watching and it knows what is best for you and me.

        Q: Does the algorithm exist?

        A: Of course it exists.

        Q: I meant, does it exist like you and me?

        A: You do not exist.

  22. It doesn’t seem to me that this is really worth worrying about. I have never heard this issue raised in the context of evolutionary theory by anyone who was remotely honest about trying to understand the subject. Complex explanations of something that is so simple and intuitively obvious are inevitably being wasted on dishonest apologists. Hair-splitting discussions about the semantics of this might be fun between peers, but in terms of communicating with the public, the flyleaf version is more than sufficient to flush out the trolls.

  23. I’ve always found the “both a theory and a fact” to be nothing but a bad pun. It’s like saying that the decline and fall of the Roman Empire is both a series of historical events and a book written about those events. The book may be so well-confirmed that its accuracy is beyond dispute, but the book is not literally identical to and will never “become” the events it recounts.

    Instead of “evolution is a theory and a fact”, I’d much prefer to say that evolution is just a fact, a process that actually happened and still on-going. And we have a well-confirmed theory which invokes that fact in its explanations.

  24. If a creationist tells me that Evolution is “just a theory,” I am not so sure if the best response is to retort that it is a fact, not a theory. I fear this can too easily be dismissed as a semantic trick.

    Another reply could be: “Yes, it’s a theory; but it’s a theory supported by mountains of evidence. You don’t even have a theory. All you have is a belief in magic. You have no way to verify the creation account in your 2000+ year old book. An account written by unknown people, based on stories from other unknown people. But the facts in the Book of Nature can be verified. The Theory of Evolution could be disproved by those facts. But so far, nobody has found any fact that disproves Evolution. Do you happen to know one?”

    Put them on the defensive, I say.

    1. Yes, be specific too… “What is your theory’s explanation for Batesian mimicry?”

      The answer to such a question will throw into sharpest relief what they are doing compared to what scientists are doing.

    2. Well, I am waiting for the JWs to turn up on my doorstep to tell me that “Evolution is only a theory, blah blah”. Alas, it was 2002 the last time any came, and they were so upset when they left that I suspect that I have been black-listed. 🙁

      But if they do, I shall ask them if they ever travel anywhere by plane – and when they say yes, ask them “Well then, doesn’t it bother you that the Theory of Aerodynamics is only a theory?” and watch their reaction.

  25. In the end, it’s a semantic issue. Technically, evolution is not a theory, but there are theories (or is a theory) of evolution. There is the fact of evolution, which makes it correct to say that evolution is a fact; but after that, it’s a question of how it works. For that, we have theories of evolution. Gravity is not a theory; there are theories of how it works. Gravity is a fact, as well.

  26. The variety of approaches in the comments here seems only to support Richard’s encouragement for avoiding the theory part entirely.

    OTOH, I don’t really see how that’s possible, since all our “opponents” are primed to attack with the “just a theory” semantic getcha which inevitably leads to having to have the “difference between theory & fact” talk.

    It might be somewhat helpful to wait and see whether that attack arises rather than tackling it automatically in every speech, though.

      1. Excellent point!

        While I’m always telling my daughter to question the motives of those who put her on the spot (she attracts a lot of judgmental types), I’m almost always guilty myself of jumping in to answer a question first before asking for clarification.

        Always volley! 😀

  27. Though I admire the work of both Richard Dawkins and Jerry Coyne, they advocate something I think is deeply mistaken. In their different ways they now invite us to abandon the distinction between theory and fact by declaring that evolution is not a theory but is just a fact. Why do they wish to do this? In the case of Dawkins it would appear that he has problems in dealing with thicko creationists (of course) when talking of evolution as a theory. But why drop the good theory/fact distinction just to placate the dumb?
    It is my guess that it will make not a jot of difference as far as creationists are concerned. They will simply deny that evolution is a fact: “You have your facts but I have mine!” But Dawkins (and perhaps Coyne) will have intellectually impoverished themselves in trying to deal with this creationist relativistic nadir in thought about facts. And lets us add to the list Stephen J. Gould whom they also cite; he makes some outrageously daft remarks about what a fact is (which seem to be verificationist or confirmationist as will be seen).
    There are lots of things wrong with this position. But the real casualty is our theory (yes, theory!) of truth. What is this? On the one hand we have propositions (or statements, or beliefs; and if one goes scientific one can add models, laws, hypotheses and the like). On the other hand we have what makes any of these items true (or false); and these are, commonsensically enough, said to be facts (or to be truth-makers). They are, in effect, bits of the world. In the case of scientific models they would be real systems.
    So what is the theory of truth? Putting the two things together, it says: any proposition is true if and only if there is a bit of the world which is the truth-maker of that proposition; and if there is no such bit of the world, then the proposition is false. Now philosophers (at whom Dawkins takes an unwarranted swipe) will be familiar with these claims and may propose importantly different formulations which the unsubtle will miss. One possible formulation is the view that the world, the set of truth-makers, is made up of facts (something we need not enter into here but is seemingly supposed by Dawkins et. al.). But let us pass over philosophical in-house disputes and go to the core of what is wrong with the Dawkins/Coyne/Gould position (if I might lump these three together).
    Consider the following claim: The proposition that DNA has a triple helix structure is true iff [it is a fact that] DNA has a triple helix structure; it is false otherwise.
    Now this proposition, or theory, viz., that DNA has a triple helix structure, is something that Crick, Watson, Pauling and others would have held to be true (in the 1950s). But what we are interested in is not its being held true by anyone at a time, but whether or not it is true, or is false, as the case maybe. So what is truth here (as distinct from evidence for the truth)? The claim is semantic and ontological. It is ontological in supposing that there is a bit of the world, viz., DNA which is a certain way, viz., it is a triple helix. It is semantic in supposing there is a relation between a proposition and some alleged bit of the world. Importantly it is NOT to be understood epistemically as Gould would have it.
    Consider now a slightly different claim: The proposition that DNA has a double helix structure is true iff [it is a fact that] DNA has a double helix structure; it is false otherwise.
    The proposition that DNA is a double helix will hold whether anyone knows it to be so or not. We do in fact now know it to be true (there is evidence). But then do not confuse our knowing that this is true, or having evidence that it is true, with its being true. There is a difference between evidence conditions and truth conditions. Not to acknowledge this is to make the common epistemic/ontological confusion. Gould makes it when he wants to tell us (as cited in Coyne): In science, “fact” can only mean “confirmed to such a degree that it would be perverse to withhold provisional assent.” But this is hopelessly misguided and is to be avoided. A fact is a fact whether the proposition that expresses it has any, or no, degree of confirmation.
    So, what is the upshot of this? One standard theory of truth turns on a relationship between what we say and how the world is. And this holds even for our scientific theories: these are amongst the things we say about the world. And the world, if it is obliging, will make a theory true, or let the theory have some degree of truthlikeness. If the world is not obliging, as it often is, it will make a theory false. To say that some theory (or set of statements), such as (the theory of) evolution, is not really a theory at all but is a fact, is to lose this distinction.
    Is anything gained by dropping the distinction? There is no good reason since it invites confusion. If one’s aim is to deal with ignorant creationists, it is not as good reason at all.
    The points made above are very truncated and need a lot more space to spell them out. But they are the beginnings of a reply to the misunderstandings that some now want to promote concerning two different matters: theories (or more generally sets of propositions) and the world that makes them true, or false. My advice is to think again and not to denude oneself of a good distinction. If creationists do not get it, then let them be damned.

  28. I agree that saying it’s a “fact” is probably the right intuition, but suspect it has to do with how humans generally apprehend “what is”. The quirky problem might sit in the domain of cognitive science, linguistics or psychology and their interdisciplinary spin-offs.

    We know that Naive Realism is false – the notion that we are observing things and then assume they “just are”. Our brains evolved as excellent map-making machines that constantly “propose” a model of what we experience which is run in brute-force mode against the weather of reality that rains into our minds. So first, we have to accept that we are being “rained into”, and are completely passive in this regard. We only move some slits around to decide from which side our brains are wetted with information.

    The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself. – Bertrand Russell

    Across the ages, people believed in the notion that we cast out “eye-rays” to see things which gave rise to the folkore of the evil eye. I suspect there is similar intuition where we beam some kind of mental-ray to scan reality to learn how it is like. And that this could account for the difference between direct experience (“facts”) and “theory” that is assembled after study. But when when this doesn’t happen, in what way does the stuff that arrives in our brains differ from some other stuf that arrives in our brain?

    I believe the difference are in the complexity of the models only – says the model dependent realist (or in my version, model dependent pragmatist). In reality, there are no “trees” in evolution. Nothing in evolution really “splits”, and there aren’t any “pools” that could do the splitting, either. We are equipped, through evolution, with “proto-language” model-making faculties which seem versatile enough to use them as building blocks for “higher up” more complex models. These models seem to be filled with content by analogy making faculties that compare perceptions. Things that appear “alike” are placed together, until a landscape of concepts with blurry outlines arises.

    There might not be a meaningful difference between the “deeper” model making and the “higher” up one, that would allow for a truly separate notion of fact and theory. Some cognitive scientists propose we use metaphors intuitively to take a concept already known and stretch it to capture some area of understand that is currently in the dark, as I did in my writing so far: and instead of complicated explanation what really happens, we say “tree of life” and people “get it” because we have internalized a highly abstract “branching” and thus “splitting” of things, which itself makes use of deeper (and older) metaphors, like “Time As Space”. Only because we internalized to mental-visualize time as spatial, we can figure out that tree-branches are time-lines of sorts that “split”. And of course we need to talk about “laws”, or how stuff is “selected” (these are metaphorical uses on closer inspection, too).

    What cognitive scientists etcetera are turning up seems like an interesting area for biologists to learn about, since evolution deals with such terms all the time, and more: “species” that move through graded cateogries across time, i.e. something is a dinosaur, then leaves prototypical features of dinosaurs behind, crosses the blurry border into the next blurry mental category of birds, meanders on the outskirts of the new cateogry and moves slowly towards the prototypical centre of the bird category, until it arrives at centre were the mental representations of “typical” birds reside.

    I’d say, with creationists and the likes, the talk should be about “what is”, and which is what we know about it. They are not specialized enough to take them into the realm of the theory. They also strike me as of the naive realist variety, and thus confuse map with territory all the time, even so much that story and metaphor are indistinguishable to them from what they are meant to capture. If that’s all the same to them, then go with “as fact”.

    Ugh, I tend to be enthusiastic about some stuff and then write too long. Sorry about that (my excuse: I do it rarely enough)

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