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Wednesday, July 31, 2019

Reactionary fringe meets mutation-biased adaptation.
5.3. How history is distorted.

This is the ninth in a series of guest posts by Arlin Stoltzfus on the role of mutation as a dispositional factor in evolution. Click on the links in the box (below) to see the other post in the series.

Reactionary fringe meets mutation-biased adaptation.
5.3. How history is distorted.

by Arlin Stoltzus

In his famous Materials for the Study of Variation, Bateson (1894) refers to natural selection as "obviously" a "true cause" (p. 5). Punnett (1905) explains that mutations are heritable while environmental fluctuations are not, concluding that "Evolution takes place through the action of selection on these mutations" (p. 53). De Vries begins his major 1905 English treatise by writing that ...
"Darwin discovered the great principle which rules the evolution of organisms. It is the principle of natural selection. It is the sifting out of all organisms of minor worth through the struggle for life. It is only a sieve, and not a force of nature" (p. 6)
Morgan (1916), in his closing summary, writes:
"Evolution has taken place by the incorporation into the race of those mutations that are beneficial to the life and reproduction of the organism" (p. 194)
Reactionary fringe meets mutation-biased adaptation
1. The empirical case
2. Some objections addressed
3. The causes and consequences of biases in the introduction process
4. What makes this new?
5. Beyond the "Synthesis" debate
    -Thinking about theories
    -Modern Synthesis of 1959
    -How history is distorted
    -Taking neo-Darwinism

    -Synthesis apologetics
6. What "limits" adaptation?
7. Going forward
The views of these leading early geneticists were not a secret: they were published, cited, and discussed. All 4 were awarded the Royal Society Darwin medal in the period from 1900 to 1930.

So, why does the evolutionary literature tell us that the early geneticists ("mutationists") rejected selection and believed in evolution by mutation alone (e.g., Dawkins 1987, p. 305 of The Blind Watchmaker; Cronin 1991, p. 47 of The Ant and the Peacock; Ayala and Fitch 1997; Eldredge 2001, p. 67 of The Triumph of Evolution; Segerstråle 2002, Oxford Encyclopedia of Evolution 2, pp. 807 to 810; Charlesworth and Charlesworth 2009)?

How does history get distorted? What can we do about it?

Synthesis Historiography

According to another story, opponents of Darwinism suffered from "typological thinking" or "essentialism," preventing them from using "population thinking" to understand systematics and evolution. Historian Mary Winsor (2006) begins her piece (below) by explaining how the Essentialism Story was "fabricated":

Self-serving Synthesis stories have become so notorious among historians that there is even a a name for them—"Synthesis Historiography" (Amundson, 2005). In Synthesis historiography, Darwin's followers discover important truths about evolution, establishing a permanent orthodoxy, while intellectual opponents behave irrationally and espouse views with obvious flaws.

The Mutationism Story is another Synthesis fable. In reality, the early geneticists inaugurated genetical thinking about evolution. Between 1900 and 1920, they conceptualized the biological species concept, the Hardy-Weinberg equilibrium, the allelic selection model, and the probability of fixation (Stoltzfus and Cable, 2014; Provine, 1971). When little Ronny Fisher was still in school, Bateson and others were considering a multiple-factor Mendelian explanation for continuously varying traits, and contemplating their gradual evolution.

Yet in Synthesis Historiography, all good things come from Darwin and his followers, requiring a bold fiction in which the early geneticists reject selection, which Fisher later reconciles with Mendelism. The credit for introducing 20th-century views of variation and heredity is assigned, not to any geneticist, but to 19th-century physiologist and infamous mouse-torturer August Weismann, whose non-Mendelian views are described by Winther (2001). The period of discovery and innovation from 1900 to 1920 is depicted as the Eclipse of Darwinism, a period of darkness when the world was deprived of His light.

The above timeline of "notable people who have contributed to evolutionary thought" (from a popular education resource) reflects Synthesis historiography. I have added a pink rectangle enclosing the birth year of anyone 25 to 60 years old-- the prime of a scientist's life—when genetics was discovered, thus implicating de Vries (1848), Johannsen (1857), Bateson (1861), Cuénot (1866), Morgan (1866), and Punnett (1875). No timelines begin in the box, i.e., the early geneticists have been erased from history, like disavowed Soviet bureaucrats.

Normality drift and back-projection

Mayr's historical fictions are brazen, but most distortions emerge passively, when ordinary scientists assume, incorrectly, that the old language was intended to cover current results, that the old theories were broadly conceived to cover all reasonable possibilities, and that dead authorities looked at evolution the way we do today.

For instance, contemporary scientists may use "Darwinian evolution" or "Darwinian adaptation" (e.g., here or here) to refer to lucky mutant models of de Vriesian aptation, not realizing that Darwin and his followers deprecated this mode of change, which they called "pre-adaptation" or "random pre-adaptation" (see Stoltzfus, 2017).

Normality-drift is also illustrated by the use of "Fisher's geometrical model" (e.g., here, here, or here) to refer a model that rejects Fisher's assumptions and subverts his conclusion (for a longer explanation, see Stoltzfus, 2017 supplement). In the original model, the size of an allelic effect determines the chance of being beneficial, which is negatively correlated with effect-size-- the smallest effects having the highest chance. From this, Fisher argued that the smallest changes are the most likely, in support of natura non facit saltum.

Fifty years later, Kimura re-cast Fisher's argument in a stochastic origin-fixation framework, inducing a second effect, positively correlated with effect-size, due to the higher chance of fixation of beneficial mutations with larger effects. This combination results in an intermediate optimum, undermining Fisher's conclusion. With further modifications, "Fisher's" model is now interpreted to mean that the distribution of changes fixed in adaptation is roughly exponential-- a few large changes and many small ones--, with the larger changes tending to happen early in an adaptive walk (Orr, 2005).

Meanwhile, to accommodate changing views, history is being rewritten so that the position of Darwinists was never natura non facit saltum, but includes jumps corresponding to macromutations, i.e., gradualism has been redefined to overlap with the "some jumps" saltationism of Bateson or Huxley (e.g., Chouard 2010; Futuyma, 2017; but Orr, 2005 portrays this issue accurately; see Why Size Matters).

Back-projection is pernicious and difficult to avoid. I have done it myself, in regard to the following
"Probably the most effective aid in establishing new genes lies in their repeated production by independent mutations.  A gene produced twice by mutation has twice as good a chance to survive as if produced only once." (Shull, 1936, Evolution, p. 140)
Previously, I interpreted this to mean that the early geneticists grasped some of the implications of biases in the introduction process. However, upon re-examination, I find Shull's argument unclear, and it is less like a theory of variation-biased evolution than like a plausibility argument for evolution by mutation and survival. That is, rather than imagining a world with two classes of mutations with different rates (imposing a bias on evolution), he seems to be contrasting two possible worlds, one with mutation rates so low that most of the mutations only get a single chance to succeed or fail, and another world in which most of the mutations happen multiple times.

An example

Finally, let us return to TREE's hatchet piece, whose authors reject the idea that the theory of Yampolsky and Stoltzfus is new:
Haldane (1927, 1933) fully presents the implications of biases in the introduction process, 70 years before Yampolsky and Stoltzfus, and this theory was then invoked by Mayr and Simpson to explain how variation imposes biases on adaptation. Clearly, this is already part of the Modern Synthesis.
I'm just kidding! They do not say that, because






Instead, they say something indirect and misleading:
"It is simply not true that the architects of the modern synthesis were unaware of the potential role of novel mutations in the evolutionary process because mutational bias was already discussed in Haldane's and Dobzhansky's early papers [19,74,75]. For instance, Dobzhansky discussed the possible role of mutation bias (expressed as similarity in germ plasms) as a potential explanation for parallel geographic variation in various species of lady-bird beetles."
This deceptive framing conflates people with theories, and focuses on a part or a premise of the theory, while ignoring the inner logic that leads from premises to conclusions. The authors assume that, if someone notices that not all mutation rates are the same (mutation bias), they will grasp the implications of biases in the introduction process. This is a fallacy. Before we know a theory, we are like the blind men in the parable who identify the parts of an elephant, but cannot conceive them as an integrated whole.

Nevertheless, let us consider what the cited sources—Haldane (1927, 1933) and Dobzhansky (1933)—have to say about the possible role of biases in the appearance of novel mutations in determining the course of evolution.

Haldane (1927) addresses the probability of fixation for a new mutation, and a mutation-selection balance model. He invokes opposing-pressures thinking, not biases in the introduction process, concluding:
"Mutation therefore determines the course of evolution as regards factors of negligible advantage or disadvantage to the species. It can only lead to results of importance when its frequency becomes large."
That is, Haldane derives the classic view that mutational effects require neutral evolution or high mutation rates. Strike one.

The second piece, Haldane (1933), begins by listing its 3 topics:
  1. "Evolution due to a mutation rate so large as to cause the spread of a disadvantageous character . . .
  2. Primary effects of the spread of genes nearly neutral from the point of view of selection . . .
  3. Secondary effects of frequent disadvantageous mutations."
None of these is the right topic. Strike two.

Dobzhansky (1933) reports on a quantitative (but non-genetic) survey of natural variation in the patterns of spots on the elytra (wing-covers) of different species of lady-beetles. He finds similar patterns of phenotypic variation in different species, and suggests an explanation:
"As stated above, there is observed a parallelism in the variability of the related species and genera. Homologous varieties of different species may be more similar to each other in appearance than the different varieties of the same species. This parallelism is, probably, due to the essential similarity of the germ-plasms of the related species."
This is more promising. Dobzhansky is referring obliquely to the effect of parallel variational tendencies in generating similar patterns of intra-specific variation in related species. The context makes clear that Dobzhansky (1933) likes Nikolai Vavilov's (1922 [PDF]) law of homologous series in variation, cited as a "rule" on page 1:
"Large groups of related species and genera exhibit parallel series of patterns, upholding the rule of homologous series in variation, formulated by Vavilov (1922)"
What a "homologous" ("parallel") series means is that one species has varieties A, B, and C, and a related species has corresponding varieties A', B', and C'. Vavilov's (1922 [PDF]) theory held that
"Variation does not take place in all directions, by chance and without order, but in distinct systems and classes analogous to those of crystallography and chemistry.  The same great divisions into orders and classes manifest regularities and repetitions of systems" (p. 84)
That is, Vavilov imagined something like the periodic table of the elements, but for systematics. He proposed a research program of identifying the pattern of variant forms characteristic of a taxon, and then looking for missing forms to complete the pattern.

In other words, Dobzhansky (1933) is not advocating the Modern Synthesis, but an earlier mutationist theory. This illustrates why it is a mistake to use people as proxies for theories.

Furthermore, Vavilov's theory is not explicit about population genetics: one does not know whether the proposed effects require high mutation rates or neutrality.

Thus (returning to the argument in TREE's hatchet piece), for Dobzhansky (1933) to know and even to like some of the thinking of the mutationists does not magically induce knowledge of the theory of Yampolsky and Stoltzfus (2001), much less make it part of the Modern Synthesis, clearly a repudiation of mutationism. Strike three.

This argument from TREE's hatchet piece is not a case of casual back-projection: the authors crafted an entire paragraph that invoked specific historic sources, yet the sources undermine their claim. What is going on here?

To understand how this behavior emerges, imagine that we have a strong prior belief that everything valuable comes from tradition and traditional authorities, e.g., we might believe that
". . . the major problems of the field have been solved. We understand both the nature of the mutational processes that generate novel genetic variants and the populational processes which cause them to change in frequency over time -- most importantly, natural selection and random genetic drift, respectively . . . no serious evolutionist will now defend once prevalent views such as orthogenesis (predetermined evolution) or the inheritance of acquired characteristics . . . we will never again come up with concepts as fundamental as those formulated by the 'founding fathers' of population genetics (Fisher, Wright and Haldane), or do experiments as path-breaking as Dobzhansky's demonstration of natural selection acting on polymorphic chromosome inversions." Charlesworth B. 1996. The good fairy godmother of evolutionary genetics. Curr Biol 6:220.
If our faith in the fullness and authority of tradition has reached this upper limit, we will respond to the claim of a new principle with unyielding skepticism, as if it were a claim of finding a unicorn or being abducted by aliens. When faced with evidence that Haldane found a unicorn (argued against the efficacy of tendencies of variation) or that Fisher was abducted by aliens (ignored the potential importance of biases in the introduction process), we will be confident that the evidence must have some other explanation, even if we can not prove it.

The deceptive attributions in TREE's hatchet piece arise, apparently, because the authors are operating near the Charlesworth limit, with full confidence that contemporary scientists cannot possibly have formulated a new principle, and that traditional authorities must have known this. To maintain this belief, the authors have misinterpreted Haldane (1927, 1933) and Dobzhansky (1933).


When we confront an issue older than a generation, we necessarily act as historians, and this requires an awareness of distorting factors. In normality drift, the meaning of old terms or concepts shifts unconsciously when the terms are applied to new findings. In back-projection, contemporary beliefs are projected anachronistically onto intellectual ancestors. The effect of these distortions is to conceal change and to blur historically important distinctions.

In addition to these little lies, there are the big lies of Synthesis Historiography. The connection between the two is that Synthesis stories feed a cultural identity defined by a shared sense of always having been on the right side of things, part of a great tradition of rightness going back to Charles Darwin: when scientists identify with this legacy of rightness, they are naturally inclined to accept normality-drift and to engage in back-projection.

The remedy for such inclinations is to adopt an attitude of scholarly skepticism. We have an obligation not to promote dubious historical claims, but to demand precise evidence.

What does evidence look like? In recent posts, we have seen multiple examples of statements from historic texts that clearly convey the inner logic of theories, and which reveal the know-like-love relationships of persons to theories.

Most scientists do not have time to pore over the historical literature searching for this kind of evidence. However, being a rigorous consumer of evidence is much easier than being a producer: one simply demands that textual evidence demonstrates exactly what is being claimed, i.e., one evaluates meta-scientific claims as carefully as scientific claims.

1 comment :

Arlin said...

A couple of links need to be fixed here. The first example of a misuse of "Darwinian" should be this.

The link to the popular education resource is here.