Three kinds of adaptationism

Arlin Stoltfus wrote an excellent book where he makes the case for mutationism—the idea that the course of evolution is determined by the occurrence of particular mutations and not by adaptation based on an infinite supply of random mutations.

Part of his argument relies on refuting adaptationism, or the idea that much of the history of life is due to adaptation (natural selection). He describes three different kinds of adaptationism in his book (p. 39) and I think it's useful to know them.

The most obvious kind of adaptationism is the belief that adaptation is actually pervasive in nature. A scientist might adopt this position of empirical adaptationism on the grounds of observations indicating that organisms are pervasively adapted, or perhaps from a theoretical understanding of the mechanism by which adaptation always prevails.

Arlin goes on to say that empirical adaptationists tend to believe that neutral evolution doesn't happen and that all appearances of neutral adaptation can be explained by subtle adaptive processes such as hitchhicking. I think this view is common among those who study the evolution of highly visible morphological traits in large plants and animals.

Methodological adaptationism holds that, whether adaptations are common or rare, one must study them because this is the only effective way to do evolutionary research. In his defense of the adaptationist research program against the famous critique by Gould and Lewontin (1979), Mayr (1983) makes this explicit:

When one attempts to determine for a given trait whether it is the result of natural selection or of chance (the incidental byproduct of stochastic processes), one is faced by an epistemological dilemma. Almost any change in the course of evolution might have resulted by chance. Can one even prove this? Probably never. By contrast, can one deduce the probability of causation by selection? Yes, by showing that possession of the respective feature would be favored by selection. It is this consideration which determines the approach of the evolutionist.

It's clear to me that Mayr is referring to a particular kind of evolutionist; namely, one like him who concentrates on studying birds in the field. Mayr is not a big fan of "beanbag genetics" or any kind of molecular evolution so his version of methodological adaptationism is similar to empirical adaptationism except that he defends it on the grounds that adaptationism is the only method of evolution that can be effectively studied and not on the grounds that neutral evolution doesn't occur.

However, in 2001 he wrote the following on page 199 of What Evolution Is.

Evolution involves the fitness of individuals and populations, not of genes. When a genotype, favored by selection, carries along as hitchhickers a few newly arisen and strictly neutral alleles, it has no influence on evolution. This may be called evolutionary "noise" but it is not evolution.

This brings us to Arlin's third kind of adaptationism.

An explanatory adaptationist may allow the possibility that adaptation is not pervasive, and may allow the methodological possibility of studying evolution in other ways (e.g., using neutral models) while still insisting that what matters most is to explain adaptation by natural selection: adaptation (in this view) is the uniquely distinctive explanation (thing to be explained) of biology, and everything else represents noise and irrelevant detail.

This is the stance that Richard Dawkins has taken over the past four decades. He argues that neutral alleles can be fixed by random genetic drift but he's not interested in that kind of evolution; it's boring. Dawkins is only interested in morphological and behavioral changes that give the appearance of design and complexity. He adopts the position that these can only be explained by natural selection.

The blind worship of natural selection is not evolutionary biology. It is arguably not even science.

Michael Lynch
Here's how Dawkins describes neutral mutations on page 332 in The Greatest Show on Earth.

A neutral mutation is one that, although easily measurable by molecular genetic techniques, is not subject to natural selection, either positive or negative. ... They might as well not exist as far as the animal's welfare is concerned.

This is similar to the 2001 position of Ernst Mayr. It doesn't reflect the reality of evolution. It's simply a reflection of the interests of the authors. Explanatory adaptationism is just another way of saying that you are only interested in natural selection so you dismiss all other mechanisms as noise. I'm pretty sure that those evolutionary biologists who study molecular evolution and/or evolutionary theory are just as interested in neutral evolution as they are in natural selection so they tend to dismiss Dawkins as just noise.

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