During the 1950s and 60s, evolutionary biologists began to attribute a greater and greater role to natural selection, and correspondingly less and less a role to alternative evolutionary agents. Empirical grounds cited in support of the change in attitude consisted primarily of selectionist reinterpretations of evolutionary changes originally attributed to other evolutionary agents. In order to distinguish the respects in which the increased emphasis on natural selection was justified and unjustified, two distinctions are relied on. These are, first, the distinction (...) between pursuing an hypothesis and accepting it, and second, the distinction between what is reasonable/rational as far as individual scientists are concerned vs. what is reasonable/rational as far as the scientific community is concerned. It was rational for at least some individual scientists to pursue exclusively selectionist accounts on the basis of the selectionist successes in question, although it was not rational for any of them to accept the hypothesis of the all-importance of natural selection on those meager grounds. Moreover, although it was reasonable for at least some individual evolutionary biologists to invoke the selectionist successes in question in pursuit of further selectionist accounts, it was not reasonable for the entire community of evolutionary biologists to pursue exclusively selectionist accounts on those grounds. (shrink)

Two decades ago, the eminent evolutionary biologist George C. Williams and his physician coauthor, Randolph Nesse, formulated the evolutionary medicine research program. Williams and Nesse explicitly made adaptationism a core component of the new program, which has served to undermine the program ever since, distorting its practitioners’ perceptions of evidentiary burdens and in extreme cases has served to warp practitioner’s understandings of the relationship between evolutionary benefits/detriments and medical ones. I show that the Williams and Nesse program more particularly embraces (...) the panselectionist variety of adaptationism (the empirical assumption that non-adaptive evolutionary processes are causally unimportant compared to natural selection), and argue that this has harmed the field. Panselectionism serves to conceal the enormous evidentiary hurdles that evolutionary medicine hypotheses face, making them appear stronger than they are. I use two examples of evolutionary medicine texts, on neonatal jaundice and on asthma, to show that some evolutionary medicine practitioners have allowed their fervent panselectionism to directly shape their recommendations for clinical practice. I argue that this escalation of panselectionism’s influence is inappropriate under Williams’ and Nesse original stated standards, despite being inspired by their program. I also show that the examples’ conflation of clinical and evolutionary considerations is inappropriate even under Christopher Boorse’s controversial evolution-rooted concepts of disease and health. (shrink)

In 1968, Motoo Kimura submitted a note to Nature entitled “Evolutionary Rate at the Molecular Level,” in which he proposed what has since become known as the neutral theory of molecular evolution. This is the view that the majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral or nearly neutral alleles. Kimura was not proposing that random drift explains all evolutionary change. He does not challenge the view that natural selection explains adaptive evolution, (...) or, that the vertebrate eye or the tetrapod limb are products of natural selection. Rather, his objection is to “panselectionism’s intrusion into the realm of molecular evolutionary studies”. According to Kimura, most changes at the molecular level from one generation to the next do not affect the fitness of organisms possessing them. King and Jukes (1969) published an article defending the same view in Science, with the radical title, “Non- Darwinian Evolution,” at which point, “the fat was in the fire” (Crow, 1985b). The neutral theory was one of the most controversial theories in biology in the late twentieth century. This chapter will review the debate over the netural theory subsequent to Kimura. (shrink)