Standing On Darwin’s Shoulders: The Nature of Selection Hypotheses

Abstract

“Standing on Darwin’s Shoulders” is about the information we need to reject or confirm selection hypotheses. Sexual selection remains important, and contrary to very old and recent claims that Darwin’s ideas cannot explain the origins of fancy traits, Darwin was not wrong, even if other hypotheses might also explain fancy traits. The problem seems to be that many readers seem to lack appreciation for the power of a good, that is, a well-constructed, testable hypothesis. To be a good hypothesis does not mean that it needs to be the truth, but only testable (or potentially testable). My main point is that what’s needed to resolve the recent state of conflict over selection of whatever name is to say as precisely as possible the details of the requisite assumptions so we can get on with testing the fundamentals of how selection works. The fundamentals of selection hypotheses are assumptions about (1) heritable variation among the units of selection, (2) the environmental and/or social circumstances that (3) affect differential probabilities of survival and reproductive success of the units of selection. Selection is simple. For example, if traits of individuals are variable, if traits are heritable, if environments (abiotic, biotic, social, etc.) vary so that some individuals have a higher probability of survival or reproduction in the environment they experience because of their trait variation, natural selection has occurred. Likewise, if individuals within a sex in the same species vary, if traits are heritable, if social environments vary so some individuals have more or better mates than others and thus greater probabilities of reproductive success, sexual selection has occurred. Thus, sexual selection hypotheses are not “systems of belief” or an associated chain of cascading ideas as Roughgarden recently claimed, but rather deductive hypotheses, admirably vulnerable to empirical tests of within sex differential fitness associated with “reproductive competition”—a hypothesis against which we can test nature. If we see more or more clearly than Darwin, it is because we stand on his broad and high shoulders!