The Akela-effect – Is there an evolutionary benefit from senators in mammals?

A characteristic feature of the life history of humans and some other species of social mammals is a long post-reproductive period. This condition is of a physiological nature in females (menopause), whereas in males it is largely of a behavioral nature. We discuss the hypothesis that old, post-reproductive individuals in these species may act as repositories of acquired knowledge, thereby providing an evolutionary benefit for their group. According to this view, the group's investment into the care for their older members is overcompensated by the benefits gained from the experience of these individuals (“senators”). This phenomenon is suggested to be largely independent from the degree of genetic relatedness within the group. We put forward a list of several necessary preconditions for the senator phenomenon to evolve. The presence or absence of these preconditions can be studied empirically.