In a preindustrial context, the mate choices of women are controlled by their parents, who require evidence of wealth and of ability to generate wealth from prospective sons-in-law in order to grant access to their daughters' reproductive capacity. As a consequence, male siblings have to compete among themselves for controlling family resources required for successful reproduction. This competition increases interfamily conflict, decreasing each of the siblings' inclusive fitness. Moreover, the sharing of resources among brothers reduces the chances that each one will be able to gain access to a high-quality female and/or to mate polygynously. It is proposed that male homosexuality has evolved to increase the reproductive success of male siblings and to decrease interfamily conflict. That is, by having a homosexual orientation, a younger male sibling increases his inclusive fitness by reducing competition over resources, whereas his older brothers enjoy higher reproductive success by having more resources available for reproduction. Finally, the reproductive costs of this sexual orientation are kept low by the elevated probability that a homosexual man will find himself in an arranged marriage where he is likely to have children.
- Fraternal older-brother effect
- Homosexual orientation
- Interfamily conflict
- Male homosexuality
- Parental choice