Some thoughts on the conceptual immune system of the “Synthesis”

As noted in Bad Takes #3, there is a long tradition of dismissing internalist-structuralist thinking on the false grounds that such ideas are necessarily appeals to teleology or mystical inner urges. If an alternative theory can be dismissed in this manner a priori, as an absurdity, then no further effort is required: no complex theoretical modeling is required, no time-consuming experiments, and no difficult analyses of empirical data. Instead, one simply considers a caricature of the alternative theory, dismisses it as absurd, and goes back to assuming that selection is the ultimate source of meaning and explanation in biology.

Indeed, a key part of the conceptual immune system of the neo-Darwinian thought-collective is a series of facile arguments, each representing some type of excluded-middle or false-dilemma fallacy.

To reject thisArgue against this versionIgnoring this version
SaltationEvolution only takes leaps; new features must arise fully formedEvolution normally includes steps or jumps reflecting distinctive variations
CatastrophismThe emergence of key innovations or higher taxa requires catastrophes (revolutions)Non-normal catastrophes play a disproportionate role in major evolutionary episodes
MutationismEvolution is driven by mutation pressure without selectionThe timing and character of evolutionary change strongly reflects the timing and character of mutation events
OrthogenesisEvolution moves in a pre-determined straight line due to mystical inner urgesThe course of evolution strongly reflects mutational-developmental channeling of variation

In the long history of evolutionary thinking, one can find examples in which authors advocate, or seem to advocate, ideas in both the second and third columns. If our aim is to identify, explore and evaluate theories about how the world really works, we are naturally drawn to the best version of a theory, not the stupid version most easily knocked down by facile arguments, i.e., a genuine approach to scientific inquiry entails a focus on the third column.

However, if we want to understand how a thought-collective perpetuates itself decade after decade, we need to understand propaganda. Within the neo-Darwinian thought-collective, the focus is on arguments against the theories in the second column, used to reject what Dawkins calls the “doomed rivals” of neo-Darwinism. In Synthesis propaganda, these excluded-middle arguments are used to maintain the all-important TINA doctrine: There Is No Alternative.

In a healthy and diverse intellectual environment, excluded-middle fallacies have no power. However, the Synthesis created an intellectual monoculture. Within this monoculture, the labels for alternative views were repeatedly associated with bad ideas and subjected to ridicule, turning the labels into bogeymen (a bogeyman is an imaginary creature invoked by adults to scare children into compliance). Through ridicule and the fear of ridicule, the system inhibits alternative thinking and preserves the appearance, if not the substance, of a neo-Darwinian status quo. The conceptual immune system is working when gatekeepers use these terms to shut down debate, but the system also works via self-censorship: well meaning scientists, fearing they will be ridiculed as extremists— or merely fearing they will be misunderstood—, avoid using historically correct terminology like “saltation” or “mutationism” or “neo-Darwinism”, and avoid making accurate references to historic debates.


Orthogenesis appears to be the most successful bogeyman, e.g., the wikipedia page for Orthogenesis repeatedly misleads readers by suggesting that orthogenesis is intrinsically teleological or non-materialistic, in spite of the fact that the article cites, and even directly quotes, multiple scholarly sources that rebut this tendentious linkage. On the talk page, the main author refers bluntly to “God-directed evolution towards a preplanned final goal, which is what orthogenesis is about.” But this is not what orthogenesis is about. Scholarly sources cited in the article (Levit and Olsson; Ulett; Popov; Gould; Schrepfer) repeatedly identify orthogenesis as a general theory about directions that emerge from tendencies of variation, and indicate that the term has been used with a range of views from mystical and teleological to fully materialistic, with well known scientists like Cope or Eimer representing the more respectable materialistic versions. That is, historical scholars describe a general theory, but wikipedians under the influence of Synthesis culture sense that the reason the world needs a wikipedia article on orthogenesis is to serve the conceptual immune system of neo-Darwinism by documenting the foolishness of alternative views.

Self-censorship is well illustrated by scientists who reject gradualism but distance themselves from terms like “saltation” or “macromutation.” For instance, Arthur (2004), after making clear he is a saltationist, e.g., like Goldschmidt, reassures readers he wants to “make clear I am not a ‘saltationist’ like Goldschmidt” (p. 107). Orr and Coyne (1992) utterly ransacked the historic Synthesis case for gradualism yet they say this:

“We hasten to add, however, that we are not ‘macromutationists’ who believe that adaptations are nearly always based on major genes. The neo-Darwinian view could well be correct. It is almost certainly true, however, that some adaptations involve many genes of small effect and others involve major genes. The question we address is, How often does adaptation involve a major gene?”

But under natura non facit saltum, the answer to how often major-effect mutations contribute to adaptation is “almost never,” which (as Orr and Coyne already know) is incorrect. Note that one of the authors of Orr and Coyne (1992) went on to become the go-to defender of orthodoxy for science reporters (see below), and the other eventually went in the opposite direction, citing Bateson approvingly and dismissing gradualism as “little more than a mathematical convenience” (Orr, 2005). Maybe that is why the paper is at war with itself.

Svensson (2023) is deploying the conceptual immune system in the following passage:

Given the strong experimental and empirical evidence against directed mutations (Lenski and Mittler 1993; Futuyma 2017; Svensson and Berger 2019) and the failure of the early mutationists to appreciate the power of natural selection, it is astonishing that some contemporary evolutionary biologists are pushing for a revival of mutationism or mutation-driven evolution (Stoltzfus 2006; Nei 2013; Stoltzfus and Cable 2014). Mutationism was closely connected to the theory of orthogenesis…

Here Svensson encourages readers to join him in scoffing at scientists by linking them to 3 different bogeymen, none of which features in the cited works by Stoltzfus (2006), Nei 2013 and Stoltzfus and Cable (2014).[1] These authors all treat “mutationism” sympathetically, but none rejects the power of selection, e.g., the title of Stoltzfus (2006) is literally “Mutationism and the dual causation of evolutionary change”. None of these pieces invokes directed mutation or advocates what readers would recognize as orthogenesis (i.e., the excluded extreme): Svensson is simply fabricating links to two more bogeymen to increase the chances of ridicule. The piece by Stoltzfus and Cable (2014) is not science but a lengthy historical analysis that debunks the mutationism myth being employed by Svensson in the same sentence.

Importantly, the main clause in the first sentence above from Svensson does not refer to a scientific theory but to persons “pushing for revival.” That is, Svensson does not say that a scientific position is wrong, nor does Svensson express “astonishment” at an idea, but instead the author expresses astonishment at the behavior of persons, i.e., the grammar of the sentence indicates that this is an overt attempt at personal shaming. The “pushing for revival” rhetoric also misrepresents the 3 cited sources, e.g., here is the final paragraph of Stoltzfus (2006):

Nei clearly conceives of his own thinking as “neo-Mutationism”, i.e., something different from historic mutationism, and his main focus is on explaining new thinking and applying it to molecular evolution rather than engaging in historical debates. Stoltzfus and Cable (2014) argue, based on a scholarly analysis of the views of Morgan, Bateson, de Vries and Punnett, that contemporary thinking is closer to their ecumenical view than to neo-Darwinism, i.e., not pushing for revival but reporting on a retreat from a former orthodoxy, one that is easily documented (see The shift to mutationism is documented in our language).

Though the “pushing for revival” rhetoric is false and unscientific, it represents a skillful use of rhetoric by Svensson: he is directly tapping into the conceptual immune system, relying on the fact that his readers have been trained to respond with aversion to the words “mutationism”, “orthogenesis” and “directed mutation.”

Role in Synthesis tribalism

Sometimes, references to the strawman versions of non-Darwinian theories are not focused on ridiculing outsiders or doubters, but on rallying followers to align with their tribal identity. For instance, consider Futuyma (2015):

The seeming exclusivity of the ES [Evolutionary Synthesis] can be understood (and excused, if deemed necessary) only by appreciating the state of evolutionary discourse in the early twentieth century (see Simpson 1944; Rensch 1959; Bowler 1983; Reif et al. 2000). Darwinism was in “eclipse” (Huxley 1942; Bowler 1983), in that almost no biologists accepted natural selection as a significant agent of evolution. (The exceptions were chiefly some of the naturalists.)… Hugo de Vries and Thomas Hunt Morgan, founders of genetics, instead interpreted mutations as a sufficient cause of evolution… [omitted comments on Lamarckism and orthogenesis]… Those who today disparage the Evolutionary Synthesis as a constrained, dogmatic assertion that evolution consists only of natural selection on random genetic mutations within species must recognize that the authors of the Synthesis were responding to an almost complete repudiation of natural selection, adaptation, and coherent connection of macroevolution to these processes.

As an argument about scientific history, this is a chain of fallacies.[1] The first fallacy is that critics of neo-Darwinism such as de Vries and Morgan denied the agency and importance of selection, or that they accepted mutations as a sufficient basis of evolution. But let us suppose that critics of neo-Darwinism denied selection: how does that justify or explain the architects making selection all-important, the exclusive source of order and direction? Wouldn’t it have been wiser to counter the extremists with a more moderate position? That makes two fallacies. Now, set aside those two fallacies, i.e., suppose that critics denied selection and that this somehow justifies advocacy of an opposing extreme. Where does that leave us today? We now have a choice of two extreme theories, neither of which fits the evidence. The logical choice is to declare both of these dinosaurs extinct, right? Given that “excusing” is something we do for people not for theories, why does Futuyma make this a matter of literally “excusing” dead people? And given that we are called on to forgive, why does Futuyma conclude that we must direct out sympathy to one specific group of extremists rather than both?

Of course, the appeal of Futuyma’s rhetoric is based on tribalism, not logic. Synthesis Historiography tells us that, before the Great Synthesis unified the kingdom, bringing a period of peace and prosperity, there was an era of chaos and darkness called The Eclipse, when the light of Darwin was absent, with constant war between the tribes of Lamarckians, Darwinians, mutationists, orthogenesists and saltationists. In order to unify the kingdom and return the throne to the House of Darwin (the rightful rulers), the knights of the Synthesis had to purge the anti-Darwinians, who behave irrationally and hold views with obvious flaws. That is, the origin story for the Synthesis tribe has a historic battle in which the good guys use reason and evidence to beat the bad guys whose heads are full of nonsense.

In the passage quoted above, Futuyma is calling on the power of these shared cultural tropes, naming The Eclipse and all the classic bogeymen— Lamarckism, saltations, orthogenesis and mutationism— to remind tribal members which side they are on: the good guys fighting against the benighted enemies of Darwin and selection. Thus Futuyma skillfully manipulates in-group readers using a shared mythology, with arguments that will seem bizarrely illogical to an outsider.

Capturing the middle ground for Darwin

In most contexts, the system of false-dilemma arguments suffices to maintain ideological conformity and rally the faithful. However, sometimes there are doubters or rebels or merely ordinary scientists who stumble on an unorthodox result and wonder if there might be something of value in alternatives to neo-Darwinism.

In this case, gatekeepers must offer a more sophisticated argument. One common approach is appropriation: conceding some aspect of the alternative view, but describing it in different language, grounding it in familiar sources and associating it with illustrious ancestors, and insisting that this actually part of the mainstream tradition and is not the same thing as any historical alternative to neo-Darwinism.

For instance, when confronted with evidence that evolution may sometimes reflect developmental channeling of variation, the guardians of orthodoxy may admit that the evidence exists, but insist that it is not very compelling, that this is definitely not orthogenesis, and anyway, that this possibility was foreseen by Darwin’s apostles and disciples, therefore it is already part of tribal culture. Futuyma (2017) makes this type of appropriation argument, citing the following passage from Mayr:

“Every group of animals is ‘predisposed’ to vary in certain of its structures, and to be amazingly stable in others . . . Only part of these differences can be explained by the differences in selection pressures to which the organisms are exposed; the remainder are due to the developmental and evolutionary limitation set by the organisms’ genotype and its epigenetic system . . . the epigenotype sets severe limits to the phenotypic expression of such [random] mutations; it restricts the phenotypic potential. The understanding of this limitation facilitates the understanding of evolutionary parallelism and polyphyletic evolution.”

Mayr (1963) p. 608

A better historic source to cite for this idea would have been Eimer or indeed, dozens of other non-Darwinian scientists who advocated much more forcefully for a role of internal developmental biases. However, to cite Eimer would be to go outside the Synthesis tradition.

Mayr typically was disdainful of internalist theories and evo-devo— he said the developmentalists were “hopelessly confused” because they didn’t understand that development is just a proximate cause—, and he repeatedly invoked the contrary neo-Darwinian position that, because natural populations have infinite variability, when the same thing happens twice in evolution, this must be because it is the uniquely apt solution. In the above passage, Mayr appears to have gone off-script (his meaning is not precisely clear: one could interpret this as a statement about epistatic effects mediated by selection). However, Futuyma, (2017) is happy to accept the above statement as justification to fully appropriate developmental bias on behalf of the Synthesis tradition. He literally writes, “The idea that development can influence the direction of evolution was fully congenial to the architects of the ES.” Note that this is a statement about people and not about scientific theories, i.e., there is no explanation of how developmental bias follows from the shifting gene frequencies theory, or why Mayr was wrong to reject developmentalist arguments in the 1980s and 1990s. He does not even attempt such a theoretical reconciliation (for an attempt, see Amundson 2005 or Scholl and Pigliucci 2010). He quotes some people and declares on this basis that the case is closed. He is not defending any theory of causation, but defending the fullness and authority of tradition.

Even as a claim about tradition, the notion that the architects of the Modern Synthesis were “fully congenial” to the idea of internal dispositions is clearly false. For evo-devo people who fought for respectability against Synthesis gatekeepers, this must feel like gaslighting. Mayr is merely stating an idea in vague terms. He doesn’t actually use the key word “direction” in the cited passage, which is important (for those of us who think about these things) because it leaves open whether he is allowing directionally biased effects (more up than down) or merely dimensional effects (more trait 1 than 2). We can’t tell because this is just hand-waving and Mayr has not provided an explicit theory that would clarify such issues. When scientists are serious about an idea, they typically invest intellectual labor in exploring, applying, and defending an idea, clarifying their own thinking, and making important distinctions (e.g., think of how Simpson or Mayr developed terminology for modes of speciation or evolutionary rates). Did Mayr publish any research on internal dispositions? Did he inspire an evo-devo research program with his forceful advocacy of developmental bias? Did he offer a terminology to recognize different classes of bias? No, none of that. A more accurate description of historical sources would be that some of the architects toyed with orthogenesis-adjacent ideas while (more typically) advocating for the standard neo-Darwinian view that, because variation is abundant in all directions, systematic patterns reflect selection and not variation.

Let’s return to the issue of gradualism vs. saltationism. At one extreme is the position of natura non facit salta, i.e., nature does not take leaps. Thinkers such as Fisher and Darwin thought that, for practical purposes, all evolutionary changes are composed from infinitesimal effects. Darwin said that his theory would “absolutely break down” if any organ could not have been formed by a succession of infinitesimal changes. The intermediate position of historic saltationists such as Bateson and T.H. Huxley is that evolution has some jumps. The contrary extreme from gradualism, in which evolution is (for practical purposes) all large jumps, is found only as a strawman theory.

As explained in Why size matters, the gradualist position is not arbitrary for neo-Darwinism and other views that assume empirical adaptationism. If selection and variation are like the potter and the clay, with variation merely providing raw materials and selection providing shape and direction, then variation has to be composed of fine particles. If all change is small, it is possible to argue that selection governs evolution and can do anything, working from infinitesimal variation in every trait. But if evolutionary change comes in chunks, this immediately takes something out of the control of selection—the character and timing of discrete variations—, and then we need some kind of theory for the character and timing of variations in order to have a workable theory of evolution.

In other words, empirical adaptationism necessarily provokes theories of gradualism (in the sense of infinitesimalism). This is not just a logical conclusion, it is how scholars such as Beatty or Gould have reconstructed the actual development of Darwin’s thinking. Likewise, the empirical conclusion that saltations actually occur in evolution provokes the search for internalist theories that address the generation of non-infinitesimal variations. This is not just a logical conclusion, it is why Bateson cataloged distinctive variations in order to study evolution.

Darwin provided some early examples of the excluded-middle arguments outlined above. In his writings, he nearly always embellishes his case against discrete evolutionary steps by referring to them with dramatic language as “monstrosities”:

I reflected much on the chance of favorable monstrosities (i.e., great and sudden variations) arising. I have, of course, no objection to this, indeed it would be a great aid, but I did not allude [in OOS] to the subject for, after much labor, I could find nothing which satisfied me of the probability of such occurrences. There seems to me in almost every case too much, too complex, and too beautiful adaptation, in every structure, to believe in its sudden production.

Why “great and sudden”? Why not “modest”? Why not “medium-sized and sudden”? Describing saltations in provocative and negative language is a common rhetorical trick, e.g., Wright associates them literally with “miracles”:

“From assisting Prof. Castle, I learned at firsthand the efficacy of mass selection in changing permanently a character subject merely to quantitative variability. Because of this and a distaste for miracles in science, I started with full acceptance of Darwin’s contention that evolution depends mainly on quantitative variability rather than on favorable major mutations. ” (Wright S. 1978. The Relation Of Livestock Breeding To Theories Of Evolution. Journal Of Animal Science 46:1192-200.)

Note that Wright misrepresents Darwin’s position as calling for “mainly” rather than exclusively quantitative variability, i.e., natura non facit saltum.

This reliance on strawman arguments and misdirection sometimes makes it difficult to determine what Darwin’s followers actually believe. Clearly they are against monstrosities, but how large of a non-monstrosity will they tolerate? Clearly Wright is against miracles and for quantitative variability, but what exactly does that mean? When gradualism fails, will he claim that there are no miracles and insist he was right all along?

Today the issue has been turned on its head. Saltationism is now the mainstream view, but “saltationism” is still presented as the straw-man theory that all evolutionary changes are dramatic leaps, or in which major taxon-defining traits must appear in a single step (e.g., Coyne). As we have seen, the contemporary scientists who conclude in favor of saltationism on empirical or theoretical grounds insist that they are not saltationists, and they sincerely hold the erroneous belief that they are aligned with Darwin and historical neo-Darwinism.

This is what happens when people absorb the TINA doctrine, i.e., they learn the lesson that neo-Darwinism is just what is reasonable, and all the alternatives are crazy, without learning neo-Darwinism as a substantive falsifiable position. Scientists are typically agile thinkers, great at making up rationalizations: if you train them to accept that gradualism is right, they will find some way to make it right, based on whatever assumptions and definitions yield the approved conclusion. For instance, note how the issue is framed by researchers cited by Chouard:

Many researchers have welcomed the return to favour of large-effect mutations and have resurrected Goldschmidt’s long reviled idea of the hopeful monster. But they can’t ignore the small-effect mutations. “We need much more data before the issue of large versus small can be settled”, says Coyne. Kingsley, like Coyne favours a middle-ground view, in which neither large- nor small-effect mutations are ruled out. “Our work has too often been portrayed as saying that Darwin was wrong” about big leaps in adaptation, he says. But in fact, none of the traits his group has studied is completely due to the effects of a single gene.

Instead of defending the all-small position of genuine neo-Darwinian gradualism, the traditionalists now defend the not-all-large (i.e., some-small) position that one “can’t ignore the small-effect mutations.”

Likewise, in response to Shapiro’s criticism that molecular saltations speak against Darwinism, Dean (2012) objects thus:

His stance is patently unfair. Thomas Huxley famously criticized Darwin for championing too gradualist a view of phenotypic evolution. Today’s Darwinists accept Huxley’s criticism . . . Horizontal gene transfer, symbiotic genome fusions, massive genome restructuring (to remarkably little phenotypic effect in day lilies and muntjac deer), and dramatic phenotypic changes based on only a few amino acid replacements are just some of the supposedly non-Darwinian phenomena routinely studied by Darwinists.

Notice the charge of being “unfair.” Here the author has gone all the way to a purely cultural position on neo-Darwinism: there is no fixed scientific theory attached to the brand, only a cultural tradition consisting of people (Darwinians) whose beliefs may change at any time. If the right sort of people start studying saltations or invoking them, this makes saltations part of neo-Darwinism.


I could go on, but these examples should be sufficient to make the point about how the conceptual immune system works. Excluded-middle arguments based on ridicule are the first line of defense, but when scientists stumble upon the middle ground, traditionalists will claim it for tradition, even if this involves misrepresenting history and shifting the goal-posts. When apologists for tradition shift from merely rejecting strawmen to appropriating the excluded middle on behalf of tradition, this represents a genuine scientific shift that is masked by conservative rhetoric. Being able to see through the misleading rhetoric is a skill that can be learned. In the current climate of evolutionary discourse, it is a necessary skill.

Another necessary skill is courage. The secret power of the conceptual immune system is that the excluded-middle arguments rely on ridicule delivered by gatekeepers, and the aura of ridicule remains when scientists discover the excluded middle.[2] Scientists want to be respected, not ridiculed, by their peers: this threat is enough to cow most of them into voluntarily making the wrong association, in order to avoid disrespect. If you use terms like “saltation”, “orthogenesis” or “mutationism” positively (or invoke “neo-Darwinism” negatively) even if your usage is historically correct and accurate, this guarantees that you will be subjected to knee-jerk reactions of ridicule, or you will be accused of seeking attention using inflammatory rhetoric. Clearly the past generation of scientists was afraid of saying such words even when they are perfectly apt and reasonable.[3] I hope that current and future generations will not be so fearful.


  • Arthur W. 2004. Biased Embryos and Evolution. Cambridge: Cambridge University Press.
  • Dean (2012) Review of Evolution: a View from the 21st Century. Microbe Magazine (available via the wayback)
  • Gould SJ. 2002. The Structure of Evolutionary Theory. Cambridge, Massachusetts: Harvard University Press.
  • Levit GS, Olsson L. 2006. “Evolution on Rails”: Mechanisms and Levels of Orthogenesis. Annals for the History and Philosophy of Biology 11: 97-136.
  • Mayr E. 1963. Animal Species and Evolution. Cambridge, Massachusetts: Harvard University Press.
  • Orr HA, Coyne JA. 1992. The Genetics of Adaptation: A Reassessment. American Naturalist 140:725-742.
  • Popov I. 2009. The problem of constraints on variation, from Darwin to the present. Ludus Vitalis 17:201-220.
  • Ulett MA. 2014. Making the case for orthogenesis: The popularization of definitely directed evolution (1890–1926). Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences 45:124-132.


[1] For a takedown of this passage from Futuyma, see Stoltzfus (2017). Critics of neo-Darwinism typically objected to its two main vulnerabilities, natura non facit saltum and the dichotomy of roles in which selection is the potter and variation is the clay. In every alternative to neo-Darwinism, the variation-generating process plays a dispositional role. Note that, in attempting to understand what critics of neo-Darwinism believe, one must not mistake skepticism about the quality and rigor of selective explanations for doubts about the (in principle) power of selection. Bateson did not deny selection as a true cause responsible for adaptation, but he was so jaded he thought that selective explanations would always be inaccessible to scientific proof and would remain mere armchair speculation. Nei seems to have a similar position.

[2] Because ridicule is such a strong demotivator, maintaining conformity does not require a large class of aggressive gatekeepers a la Svensson. A little bit goes a long way. As explained in the introductory paragraphs, most people don’t need to be shamed directly to avoid thinking unorthodox thoughts, they will just do it on their own because, again, people want to be respected.

[3] Note that accurately depicting mutationism, neo-Darwinism, or other historic views does not require any special courage for historians or other scholars who are not striving for, and are not dependent on, the approval of mainstream Synthesis culture. Among mainstream evolutionary thinkers, Allen Orr has shown courage in quoting Bateson approvingly and in depicting gradualism correctly as an extreme position. Gould was unafraid to show sympathy to non-Darwinian thinking, but his sympathy seems more like pity when one notices how frequently Gould associates critics of neo-Darwinism (e.g., de Vries, Goldschmidt, Bateson) with behavioral disorders, reinforcing the Synthesis tribal mythology in which only crazy people reject neo-Darwinism.

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