Ageing, mate preferences and sexuality: a mini-review.

The evolutionary constraints that lead to the evolution of sexual reproduction are framed by the better repair mechanisms that repair fatal mutations, as well as the need for variable immune systems imposed on large organisms by parasites, such as viruses and bacteria. Besides the evolution of sexual reproduction, these factors also affect mate choice, especially as regards the gene complex that encodes the immune system. The need to increase both the likelihood of gametes to encounter each other as well as sufficient provision of nutrition for the offspring then leads to the evolution of two sexes: large numbers of small mobile sperms ensure that gametes meet, whereas large egg cells full of energy provide for the zygote, thus leading to a developmental advantage. The asymmetric investment in the offspring then affects not only mate choice criteria, but also cognitive strategies. Men place more importance on youthfulness and fertility than women, who regard resource holding potential as a more relevant criterion. Consequently, female jealousy is connected to endangered access to resources, whereas male jealousy is rooted in paternal uncertainty. Cognitive adaptations developed to ensure reproductive success show sex differences, such as in error management. The most obvious function of sexual behavior is reproduction. To foster the benefits for the offspring, reproduction partners should also develop an emotional bond, which is mediated by hormones connected to sexual intercourse. With increasing age, reproduction loses importance, while pair bonding functions remain relevant. Therefore, sexuality never ceases to be part of a relationship.