Reproductive conflict hypothesis
In social vertebrates, the sharing of resources among the group places limits on how many offspring can be produced and supported by members of the group. This creates a situation in which each female must compete with others of the group to ensure they are the one that reproduces. The reproductive conflict hypothesis proposes that this female reproductive conflict favors the cessation of female reproductive potential in older age to avoid reproductive conflict, increasing the older females fitness through inclusive benefits. Female-biased dispersal or non-local mating leads to an increase in relatedness to the social group with female age. In the human case of female-biased dispersal, when a young female enters a new group, she is not related to any individual and she reproduces to produce an offspring with a relatedness of 0.5. An older female could also choose to reproduce, producing an offspring with a relatedness of 0.5, or she could refrain from reproducing and allow another pair to reproduce. Because her relatedness to males in the group is high, there is a fair probability that the offspring will be her grandchild with a relatedness of 0.25. The younger female experiences no cost to her inclusive fitness from using the resources necessary to successfully rear offspring since she is not related to members of the group, but there is a cost for the older female. As a result, the younger female has the advantage in reproductive competition.
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