Darwin's species and the One-True-Peak

Today is Darwin Day. Chris at Mixing Memory has qualms about the name, and suggests "Evolution Day" as a more appropriate celebratory appellation in keeping with the spirit of Charles Darwin's scientific insights. I tend to have sympathies with Chris' point, though I would assert that Darwin was the Newton, not the Kepler, of evolutionary biology. Many scientists observed the reality of evolution and formulated "laws" before and after his time, but it was Darwin who placed natural selection upon heritable variation at the center of the process of evolutionary change over time. But Chris' point holds, science itself has evolved since that day, and I think it is politic to engage in a bit of marketing and disengage from the term "Darwinist" because of his negative baggage, both historically and contemporaneously. But, "Evolution Day" is too general I think, the supposition of evolutionary change is not a particular novel one, and evolution as a process spans all of nature on the most prosaic reading.

On to other things, PZ Myers and Evolgen point me to this mammoth essay by Niles Eldridge, who has spent much of his career being perennially associated with Stephen Jay Gould and their theory of Punctuated Equilibria (PE). PE is a controversial hypothesis in some quarters, in The pace of evolution I allude to "hillists" and "mountainists," and in large part this was a nod to the "conflict" between Gould & Eldridge and the "Old Guard" of Fisherian selectionist/gradualists headed by Richard Dawkins. Though I probably lean toward the selectionist/gradualists in many ways, I have come to feel that these disputes are predominantly semantical, matters of weight of emphasis in a word here and there, than genuinely deep fissures of substance. Eldridge's essay is an admirable corrective to those who would inflame minor irritations into paradigm shifting contentions. Nevertheless, I must note with some disgruntlement that my first encounter with the term PE was via an 8^th grade teacher who declared that he was not a "Darwinian." Books need to be sold, and at some point the rhetorical flourish overwhelmed the swell of insight generated by novel models and alternative heuristics.

Yet in the realm of the science, PE seems to be an attempt to bring a macroevolutionary sensibility to the microevolutionary discipline of modern evolutionary biology, which has been overwhelmingly genetic in orientation since the seminal papers of R.A. Fisher, Sewall Wright and J.B.S. Haldane were published around 1930. Myself, I will fess to not knowing much about macroevolution, and my model of the tree of life is far too truncated and spare for my own comfort, nevertheless, I have taken an interest in species and species concepts since reading Speciation by Jerry Coyne and H. Allen Orr. Like Evolgen I'll believe in sympatric speciation when I see it (probably happens, though I don't know how ubiquitous it is, depending on how you define species). Eldridge and Gould's ideas about the importance of geographic separation and population subdivision are not limited to those who have a broad historical conception of evolutionary processes, Theodosius Dobzhansky and Ernst Mayr both promoted theories which emphasized the importance of such phenomena in laying the seeds for speciation closer to the main microevolutionary trunk.

Which brings me to this paper by Will Provine titled Ernst Mayr: Genetics and Speciation. I stumbled upon it doing a literature search relating to the possibility of an increase in additive genetic variation after a founder effect, and the association of this sort of dynamic with Mayr's ideas in relation to "genetic revolutions." But that's for another day. Having read an elaboration on Provine's Ph.D. thesis on the details of the history of theoretical population genetics, this review was not surprising in the generality, though the details were specific to Mayr's life. In Sewall Wright and Evolutionary Biology Provine argued that both Dobzhanksy and Mayr's theoretical conceptualizations were verbal distilliations of the analytic models proposed by Sewall Wright. In this paper, as elsewhere, Provine points out that the technical rigor of population genetics is generally too high a barrier for many evolutionary biologists to scale, so they simply absorb the general lay of the land rather than making a full scale expedition into the wilds. In the context of evolutionary biology a recurring axe that Provine seems to want to grind is that most observers misunderstand the role that random genetic drift played in Sewall Wright's models. In short, Mayr initially believed that random genetic drift working stochastically within subdivided populations was responsible for the biological barriers which eventually led to incipient speciation. Evolgen has commented on Provine's rejection of random genetic drift before, and he also brought up this issue in the afterword of The Origins of Theoretical Population Genetics. In the Genetics paper Provine offers that Mayr shifted from focusing on random genetic drift to emphasizing the importance of genetic interactions, for example, statistical epistasis (interactions across genetic loci), which is in keeping with Wright's original conception. To some extent it seems that Provine has interjected into a review of Mayr's ideas relating genetics and speciation a subtext of the famous Fisher vs. Wright debate regarding population substructure and adaptive landscapes. In short, while Fisher emphasized the power of selection across genes of small independent effect operating across whole populations, Wright believed that population subdivision and interactive genetic complexes generated a more complex adaptive landscape. While for Fisher a three-dimensional plot, where the x and z axes are gene frequencies and the y (vertical) axis fitness, might resemble Mt. Fuji, gently sloping up toward one unified peak, Wright's landscape would be rugged, with multiple peaks. This idea that there might be multiple fitness peaks appealed to experimentalists like Dobzhansky and naturalists like Mayr, who saw the impact that population substructure had upon organisms in both lab and field. Fisher's response was simply that non-additive genetic effects were epiphenomena which cancelled out over the long run. These various strands have relationships with the ideas of paleontologists like Gould, who favored a primacy of contingency, and those like Simon Conway Morris who argue for the inevitable directional impulse of selection scaling the fitness slop toward the One-True-Peak.

But what those relationships are can be difficult to entangle. In the end, I suspect that those within science would be best served by ignoring the controversies and just focusing on the data and models that relate to specific phenomena as opposed to grand philosophical paradigms. Speciation is an fascinating topic, though personally I think a lot of it is obscured by semantic turf wars spawned by too much philosophy and politics drawing strength form innate cognitive biases toward typology.