I updated my thoughts on Gould's essay in 2007 [Evolution Is a Fact and a Theory] and added some more comment on the 30th anniversary [Evolution Is a Fact and a Theory].
Lot's of other people have presented their take on the facts and theories of evolution. Here's one from Richard Lenski and another from Ryan Gregory.
Evolution: Fact and Theory (Richard E. Lenski)
Evolution as Fact, Theory, and Path (T. Ryan Gregory)
Everybody has a slightly different take on the meanings of "fact" and "theory." Now Richard Dawkins enters the fray with his own views on the issue [Is it a Theory? Is it a Law? No, it’s a fact.].
He begins by quoting the definition of a scientific theory using a dictionary meaning that's not substantially different from what Gould said in 1981. Dawkins' Oxford version is ...
Theory, Sense 1: A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.Dawkins is frustrated because we haven't made any progress after half-a-century of trying to teach creationists that this is the proper meaning of "theory." He recommends a different approach ....
The party line among scientists arguing for evolution is to promote Sense 1, 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.Oops! This isn't looking good.
There's still a difference between evolution as facts and evolutionary theory. Note that I said "evolutionary theory" instead of "The Theory of Evolution." That's because it's easy to get confused when you talk about something as complex as evolutionary theory by referring to it as "The Theory." Creationist think that the history of life and common descent is what we mean when we say "The Theory of Evolution." They hear this as: "the theory that life evolved and everyone shares a common ancestor."
That not really part of evolutionary theory. The history of life is reconstructed and deduced from real data. Much if it is fact, not theory. It's a fact, not a theory, that humans and chimps descend from a common ancestor that lived about 6 million years ago. Evolutionary theory explains how this might have happened using proven mechanisms like natural selection, random genetic drift, mutation, speciation etc.
It is time for students of the evolutionary process, especially those who have been misquoted and used by the creationists, to state clearly that evolution is a fact, not theory, and that what is at issue within biology are questions of details of the process and the relative importance of different mechanisms of evolution. It is a fact that the earth with liquid water, is more than 3.6 billion years old. It is a fact that cellular life has been around for at least half of that period and that organized multicellular life is at least 800 million years old. It is a fact that major life forms now on earth were not at all represented in the past. There were no birds or mammals 250 million years ago. It is a fact that major life forms of the past are no longer living. There used to be dinosaurs and Pithecanthropus, and there are none now. It is a fact that all living forms come from previous living forms. Therefore, all present forms of life arose from ancestral forms that were different. Birds arose from nonbirds and humans from nonhumans. No person who pretends to any understanding of the natural world can deny these facts any more than she or he can deny that the earth is round, rotates on its axis, and revolves around the sun.We all know about problems with the meaning of "theory." It's often used to refer to hypotheses or even to speculation. Scientists, themselves, don't always stick to the "Sense 1" definition quoted above.
The controversies about evolution lie in the realm of the relative importance of various forces in molding evolution.
R. C. Lewontin "Evolution/Creation Debate: A Time for Truth"
Bioscience 31, 559 (1981) reprinted in Evolution
versus Creationism, J. Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983
For example, Stephen Jay Gould often spoke of the theory of punctuated equilibria and that's not a "theory" that is widely accepted by most evolutionary biologists. As a matter of fact, some of them don't even accept the "fact" of punctuated equilibria as a dominant history of speciation. This is "Sense 2" of the word "theory."
There are other aspects of evolutionary theory that are so well established they are facts in their own right. It is a fact, for example, that natural selection occurs and it is a fact that mutations occur. The aspect of evolutionary theory that applies is how these mechanisms account for the observed facts of the history of life.
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.Hmmm ... fish & chips. Tomorrow is Friday. I agree that no intelligent person could eat fish & chips .... without realizing that you are eating your cousins.
However, there are creationists who don't accept common descent so this strategy isn't going to work with them. If we are ever going to convince YEC's that life has evolved then we are forced to come to grips with the distinction between microevolution and macroevolution and we are obliged to defend the meaning of words like "homology," "evolution," "contingency," "adaptation," "speciation," etc. Most of us don't realize how much of our "facts" are tied to "theory."
Furthermore, there are many creationists who accept various forms of common descent but insist that evolutionary theory cannot account for it. These creationists range from Theistic Evolutionists—who think that God's guidance is subtle—to Intelligent Design Creationists—who think that God's handiwork can be easily detected. All of them believe that the history of life shows evidence of purpose.
Let’s simply give up on trying to explain the special scientific meaning of “theory”. It is begging to be misunderstood by laymen eager to misunderstand, and even scientists are not consistent in their usage. The ordinary language meaning of “fact” (it is a fact that New Zealand is in the Southern Hemisphere) and the scientific meaning (the evidence for evolution is so strong that to withhold assent would be perverse) are close enough to obviate confusion in the mind of all but the most doggedly pedantic philosopher. By all means postpone for another day the question of whether natural selection is also a fact. For now, when arguing with creationists, let’s sweep confusion aside by means of a strategic retreat from the word “theory”. Let’s sacrifice a pawn for strategic advantage and hammer home a clear message that everyone can understand, and which is undeniably true in the everyday sense. Evolution is a fact.I don't agree with Richard Dawkins. Such a strategy is doomed to failure.
You cannot argue with Michael Behe, Ken Miller, Michael Denton, and Francis Collins by simply declaring that common descent is a fact. They will agree with you! And when debating Young Earth Creationists you can't just declare victory by saying that you have the facts and they don't. We need to show them why we are related to haddock and spuds. That includes the evidence, how we interpret it, and how it fits into modern evolutionary theory. (For starters, you need to explain what we mean by "evolution.")
Evolution: theory, fact, or both?]. He makes a good point about the Gould description of "fact" which is, "In science, 'fact' can only mean 'confirmed to such a degree that it would be perverse to withhold provisional assent.'" Coyne points out that ...
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.)That's a good point but it doesn't just apply to YEC's. Many of us are comfortable with the ideas that evolution is purposeless and our genome is full of junk DNA. I think these are facts. I claim that everyone who is qualified to judge scientific evidence agrees. I usually refer to "knowledgeable scientists" when I argue this point.
Creationists, and ENCODE scientists, will argue that facts are in the eye of the beholder and they are right. The important point here is how to "behold" something correctly.
Here's how Jerry Coyne describes the problem with "theory."
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.”That's interesting.
My take is somewhat different. I say that natural selection is a proven mechanism of fixing alleles in a population and so is random genetic drift. And mutation is what produces variation. These mechanisms are all part of well-developed evolutionary theory, especially population genetics. Modern evolutionary theory agrees that natural selection is a mechanism of adaptation but Neutral Theory and random genetic drift play a role as well. Which process works in the real world?
We can apply our knowledge of evolutionary theory to the facts we observe about the actual history of life. The phenotypic differences between (and within) species are caused by evolution (fixation of alleles and variation) but are they adaptations or accidents? We need facts and evidence to answer those questions and there's considerable debate about the evidence. Evolutionary theory doesn't change while we debate the importance of drift and natural selection and the facts of common descent doesn't change either.
Is most evolutionary change during the history of life due to fixation of alleles by natural selection or by random genetic drift? Either one could be true. What we're asking is, given the unique history of life that we observe, which mechanism predominates using the standard definition of evolution? Does drift dominate in some species and natural selection in others?
I think the answer is clear—drift wins—but evolutionary theory doesn't stand or fail depending on the result of this debate. When the debate is resolved it will be a fact that drift is responsible for most fixations in an evolving genome. On another planet, the reverse might be true.
Jerry likes to focus on the facts when he teaches evolution ...
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 theory, evolution doesn't have to be gradual and the appearance of design can be produced accidentally. So, looking at our unique history of life—the only example we have—which theoretical mechanism best explains the data? Is it really a "fact" that the only examples we have all demonstrate that evolution is gradual? Is it really a "fact" that all examples of "design" are best explained as adaptations? What about speciation" What's the best definition of a species and are observable speciation events mainly the result of drift or selection? (Both are theoretically possible.)
I'm happy to accept that evolution is a fact and that common descent is a fact but I'm pretty sure that Jerry and I would differ on exactly how we explain those facts according to modern evolutionary theory. Richard and I would also disagree. It depends on how you "behold" the history of life.
Jerry concludes with ....
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.I guess it depends on one's interests. I will continue to debate and discuss evolutionary theory and try to explain to my students why there is controversy about the meaning of "Darwinism" and why they have to read the "Spandrels" paper. In my course, I will try and explain why some people think that epigenetics and EVO-DEVO are changing evolutionary theory. I'll try and explain why a solid understanding of evolutionary theory—especially population genetics—is necessary in order to understand the junk DNA debate.
Modern evolutionary theory explains the facts of life's history in the same way that the theory of gravity explains our solar system. You need to teach both the facts and the theory.
1. It didn't work.