Abstract
Humans, like many social species, interact with genetic relatives throughout periods of sexual maturity increasing the chance that, barring systems motivating avoidance, close genetic relatives could select one another as sexual partners. However, although suitable in several respects, close genetic relatives represent poor sexual partners due to selection pressures posed by short-generation pathogens and lethal recessive mutations. For this reason, it is likely natural selection crafted information-processing circuitry—mental software—that enabled inferential systems to estimate the probability another individual was a close genetic relative and to trade off this information against other factors influencing fitness to adaptively identify suitable sexual partners. In this chapter we discuss incest avoidance adaptations and provide a model of how human mate choice might operate.