Sexual orientation, behavioral plasticity, and evolution

The argument of Futuyma and Risch (1983/1984), that the homosexual orientation is not a distinct, evolved, reifiable trait with a genetic basis, but an expression of universal sexual and emotional drives, has validity. Yet it does not answer the question of why the development of sexual orientation has evolved to be so flexible as to allow an individual to become homosexual. It is proposed that this flexibility may result from the evolution of the capacity to learn, the complexity of the central nervous system, and behavioral plasticity in general. This theory fits the known literature better than all other evolutionary explanations of homosexuality and has interesting implications for the evolution of altruistic behavior in humans.