Evolutionary biology
Modern explanations of the origins of human sexuality are based in evolutionary biology, and specifically the field of human behavioral ecology. Evolutionary biology shows that the human genotype, like that of all other organisms, is the result of those ancestors who reproduced with greater frequency than others. The resultant sexual behavior adaptations are thus not an "attempt" on the part of the individual to maximize reproduction in a given situation – natural selection does not "see" into the future. Instead, current behavior is probably the result of selective forces that occurred in the Pleistocene.