Human suicide presents a fundamental problem for the scientific analysis of behavior. This problem has been neither appreciated nor confronted by research and theory. Almost all other behavior exhibited by humans and nonhumans can be viewed as supporting the behaving organism's biological fitness and advancing the welfare of its genes. Yet suicide acts against these ends, and does so more directly and unequivocally than any other form of maladaptive behavior. Four heuristic models are presented here to account for suicide in (...) an evolutionary and sociobiological framework. The first model attributes suicide to the extraordinary development of learning and cultural evolution in the human species. Learning may make human behavior so independent of biological constraints that it can occasionally assume a form entirely contrary to the principles of biological evolution. The second model attributes suicide to a breakdown of adaptive mechanisms in extremely stressful novel environments. The third model involves kin and group selection, arguing that in limited circumstances suicide may occur because of beneficial effects it has on other, surviving individuals who share the suicidal individual's genes. The last model suggests that suicide should be tolerated by evolution when it has no effect on the gene pool. This model holds particular promise in accounting for aspects of suicide not attributable to culture. The evidence indicates that suicide is most common in individuals who are unlikely to reproduce and unable to engage in productive activity; such individuals are least capable of promoting their genes. A complete explanation of suicide may derive only from an analysis of its biological significance. (shrink)

Patterns in the data on human sexuality support the hypothesis that the bases of sexual emotions are products of natural selection. Most generally, the universal existence of laws, rules, and gossip about sex, the pervasive interest in other people's sex lives, the widespread seeking of privacy for sexual intercourse, and the secrecy that normally permeates sexual conduct imply a history of reproductive competition. More specifically, the typical differences between men and women in sexual feelings can be explained most parsimoniously as (...) resulting from the extraordinarily different reproductive opportunities and constraints males and females normally encountered during the course of evolutionary history. Men are more likely than women to desire multiple mates; to desire a variety of sexual partners; to experience sexual jealousy of a spouse irrespective of specific circumstances; to be sexually aroused by the sight of a member of the other sex; to experience an autonomous desire for sexual intercourse; and to evaluate sexual desirability primarily on the bases of physical appearance and youth.The evolutionary causes of human sexuality have been obscured by attempts to find harmony in natural creative processes and human social life and to view sex differences as complementary. The human female's capacity for orgasm and the loss of estrus, for example, have been persistently interpreted as marriage-maintaining adaptations. Available evidence is more consistent with the view that few sex differences in sexuality are complementary, that many aspects of sexuality undermine marriage, and that sexuality is less a unifying than a divisive force in human affairs. (shrink)