When most people think about evolution by selection, they conjure up phrases such as "survival of the fittest" or "nature red in tooth and claw." These focus attention on the Darwinian struggle for survival. Many scientists, but few others, know that evolution by selection occurs through the process of differential reproductive success by virtue of heritable differences in design, not by differential survival success. And differential reproductive success often boils down to differential mating success, the focus of Darwin's 1871 theory of sexual selection.
Darwin identified two separate (but potentially related) causal processes by which sexual selection occurs. The first, intrasexual or same-sex competition, involves members of one sex competing with each other in various contests, physical or otherwise, the winners of which gain preferential sexual access to mates. Qualities that lead to success evolve. Those linked to failure bite the evolutionary dust. Evolution, change over time, occurs as a consequence of the process of intrasexual competition. The second, intersexual selection, deals with preferential mate choice. If members of one sex exhibit a consensus about qualities desired in mates, and those qualities are partially heritable, then those of the opposite sex possessing the desired qualities have a mating advantage. They get preferentially chosen. Those lacking desired mating qualities get shunned, banished, and remain mateless (or must settle for low quality mates). Evolutionary change over time occurs as a consequence of an increase in frequency of desired traits and a decrease in frequency of disfavored traits.
Darwin's theory of sexual selection, controversial in his day and relatively neglected for nearly a century after its publication, has mushroomed today into a tremendously important theory in evolutionary biology and evolutionary psychology. Research on human mating strategies has exploded over the past decade, as the profound implications of sexual selection become more deeply understood. Adding sexual selection to everyone's cognitive toolkit will provide profound insights into many human phenomena that otherwise remain baffling. In its modern formulations, sexual selection theory provides answers to weighty and troubling questions that elude many scientists and most non-scientists living today:
• Why do male and female minds differ?
• What explains the rich menu of human mating strategies?
• Why is conflict between the sexes so pervasive?
• Why does conflict between women and men focus so heavily on sex?
• What explains sexual harassment and sexual coercion?
• Why do men die earlier than women, on average, in every culture around the world?
• Why are most murderers men?
• Why are men so much keener than women on forming coalitions for warfare?
• Why are men so much more prone to becoming suicide terrorists?
• Why is suicide terrorism so much more prevalent in polygynous cultures that create a greater pool of mateless males?
Adding sexual selection theory to everyone's cognitive toolkit, in short, provides deep insight into the nature of human nature, people's obsession with sex and mating, the origins of sex differences, and many of the profound social conflicts that beset us all.