The Verbal vs. the Genetic Theory of Evolution

The answer relates to what Orr [15] calls the “curious disconnect” between the “verbal theory that sits at the heart of neo-Darwinism” and the emerging theoretical implications of evolutionary genetics. The roots of this disconnect may be found in a long historic struggle to reconcile evolutionary thinking with the emerging facts of heredity [16]. After the discovery of Mendelian genetics in 1900, this struggle took the form of a dispute between 3 concepts, all confusingly called “selection”: (1) Darwin’s pre-genetic concept of a creative force that molds traits from a blending mass of infinitesimal differences (raw materials); (2) a Mendelian frequency-shifting force that acts on true-breeding types, so that a rare type may replace a common one; and (3) a stochastic filter (a sieve or pruning hook) that modulates the chance of survival of spontaneously arising mutants, some of which get lucky.

The battle lines of this historic conflict continue to shape contemporary evolutionary discourse. Darwin’s original theory was based on a non-Mendelian view of heredity characterized by blending of environment-induced, continuous variation [16, 17]. When confronted with the complaint that selection is not creative, but merely addresses “the relative success and failure of such new forms as may be born into the world”, Darwin’s response was clear: “that may be a very good theory, but it is not mine” [18]. That is, while we may think of concepts #1 to #3 above as manifestations of an elemental Darwinian principle of selection, Darwin and his followers did not agree, and saw these as separate theories of evolution. This is why Darwin’s early followers resisted Mendelism, and rejected the mutationist view (#3) of de Vries, Bateson, and Morgan as an anti-Darwinian view without selection (i.e., without #1).

That’s an interesting and helpful perspective on the history. There does often seem to be a disconnect between the verbal theory and the underlying science. Will that disconnect ever be resolved?

1 Like

I’m confused as to why I should care what Darwin thought about anything? He was either right, in which case I care about the idea regardless of who it came from, or he was wrong, in which case I don’t care about the idea at all. But the idea is what matters, not the person. This preoccupation with the thoughts of someone who died before we knew what DNA was is silly.


It’s just history of the field. There is value in knowing that history. Of course, it would be a mistake to equate Darwin’s views with current evolutionary science.


I find the quote confusing. I don’t think Darwin’s theory relies on blending inheritance, which in fact would deprive natural selection of much of its power (and which critics pointed out at the time). Whether selection is a “creative force” depends on whether new features are built by single variations or mutations or by many slight, successive variations. In the former case, the mutationists would be correct, and selection could choose only among major phenotypes. In the latter case, selection is a hill-climbing meclhanism that in a meaningful sense does create phenotypes. (And obviously this is a continuum of effect.) Polygenic and/or additive traits take us closer to Darwin’s view than that of the mutationists.

I’m not sure what “the verbal theory” is. But we should beware of taking metaphor too literally.


Okay, that’s definitely true. But that excerpt doesn’t read as a discussion of the history of the field, it reads like the differences matter for current science. Maybe it’s clearer from the full article.


I agree but I take Arlin to be saying that Darwin’s views still influence the field in a detrimental way, as the “verbal theory” view which is a historical product of Darwin’s views, often comes into conflict with the molecular and mathematical population genetics view when you have to actually model evolution. Or something like that.

I’m not really sure what the problem is in the end. Are the people who model evolution modeling it incorrectly? Are they describing it incorrectly but modeling it correctly? As an outsider I some times get the feeling people are really wasting way too much time arguing about subjective notions and measures of emphasis and influence of different forces of evolution, with no way to objectively settle the debates because nobody is proposing ways to objectively measure a unit of “influence” on evolutionary change.

Every time I see these debates I think they’re waste of time. Literally rolling my eyes. And yet people obsess about it. Is drift more important than selection? More important TO WHAT? How do we measure importance? Are genes more important than phenotypes? Who says and why? Why even fckin care? Do something useful. MOVE ON!


I think that there is an extent to which some of the description of things gets mashed together, with some of Darwin’s language being used to describe things he would not have agreed with. But I don’t see any problem with that, unless you’re of the view that words can never change meaning and selection must always and forever only mean what Darwin wanted it to mean. It’s like complaining about talking about genes when Mendel didn’t know about DNA. Or mutations when Morgan didn’t know about DNA.


There is a problem when it comes to communicating evolutionary science to non-experts, and perhaps also students. Because if the disconnect is not clear, it can lead to deep confusion on fairly critical things.

What is the root cause of that problem?

Is it that the communication is unclear because it puts too much emphasis on discarded ideas, or is it that other influences are introducing misconceptions that need to be overcome?

1 Like

I think the root cause is the gap between the verbal theory and the scientific findings. Experts navigate that gap just fine, but it present an opportunity in that perhaps we can find better ways to describe it, by defining and articulating a more precise and accurate verbal theory.

Could someone articulate just what “the verbal theory that sits at the heart of neo-Darwinism” actually is? I for one have no idea, though perhaps it’s in the Orr reference. Note also, it’s neo-Darwinism, not necessarily what Darwin was talking about.


“Verbal theory” - The only evolutionary mechanisms are those which can be understood as forces or pressures that move a population from set of allele frequencies to another; leans adaptationist.


“emerging theoretical implications of evolutionary genetics” - neutral evolution creates dynamics that are better understood in a thermodynamics sense than a mechanical sense; trends and biases emerge from the fact that some portions of state space are larger than others even though there are no fitness advantages involved. Constructive neutral evolution is offered as an example.

If I’m understanding the distinction correctly, an analogy might be made to Plinko or a Galton board. The movement of individual chips/balls is governed entirely by forces and the kind of Newtonian mechnanics one learns in high school. Those mechanics do not make any one path more likely than any other path. So that particular lens does not lend itself well to a simple explanation for why some spots wind up with many more chips/balls than others. But if you think in terms of a coarse graining from the individual paths (“microstates”) to end positions (“macrostates”) and notice that some end positions have many more paths leading to them, it is easier to understand why the chips/balls tend to wind up there.

Now, I don’t fully understand why the first version is the “verbal theory” because there is plenty of math associated with it. I guess because written explanations of evolution tend towards that version? Or maybe because that version first emerged in writing and was only later formalized mathematically?


This topic was automatically closed 7 days after the last reply. New replies are no longer allowed.