Sexual Selection: Is Anything Left?

Abstract

The biological definition of what counts as sexual selection has gradually changed since Darwin introduced the concept. This paper reviews a sequence of definitions that reflect increasing knowledge of the diverse ways animals participate in reproductive social behavior. Later definitions accommodate more data than Darwin’s primary formulation. The latest approach, suggested in a catalyst meeting held at the National Evolution Synthesis Center in July 2013, distinguishes fertility selection as a density-dependent process from sexual-selection as a frequency-dependent process. The former consists of reproductive social behavior focussed on increasing the size of the reproductive pie, the later on securing a larger share of a given reproductive pie. The approach of social selection advocated here focusses on how to increase the size of the pie rather than on how to monopolize a larger share of a fixed pie. Social selection reverses the logic of sexual selection by starting with offspring production and working back to mating, and by starting with behavioral dynamics and working up to gene pool dynamics. In social selection courtship can potentially be deduced as a negotiation leading to an optimal allocation of tasks during offspring rearing. Mating pairs may form “teams” based on the reciprocal sharing of pleasure. The parent-offspring relation can be managed by the parent considered as the owner of a “family firm” whose product is offspring. The cooperation in reproductive social behavior may often evolve as a mutual direct benefit through individual selection rather than as some form of altruism requiring kin or multi-level selection.