Abstract

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.