When It Comes to Aging, Humans are Noticeably Different
Humans are long lived in comparison to other primates and similarly sized mammals. In addition some characteristics of human aging are unusual in comparison to those of neighboring species. Aging is near universal but its specific evolved manifestations are highly varied:
Women rarely give birth after ∼45 y of age, and they experience the cessation of reproductive cycles, menopause, at ∼50 y of age after a fertility decline lasting almost two decades. Such reproductive senescence in mid-lifespan is an evolutionary puzzle of enduring interest because it should be inherently disadvantageous. Furthermore, comparative data on reproductive senescence from other primates, or indeed other mammals, remains relatively rare. Here we carried out a unique detailed comparative study of reproductive senescence in seven species of nonhuman primates in natural populations, using long-term, individual-based data, and compared them to a population of humans experiencing natural fertility and mortality.In four of seven primate species we found that reproductive senescence occurred before death only in a small minority of individuals. In three primate species we found evidence of reproductive senescence that accelerated throughout adulthood; however, its initial rate was much lower than mortality, so that relatively few individuals experienced reproductive senescence before death. In contrast, the human population showed the predicted and well-known pattern in which reproductive senescence occurred before death for many women and its rate accelerated throughout adulthood. These results provide strong support for the hypothesis that reproductive senescence in midlife, although apparent in natural-fertility, natural-mortality populations of humans, is generally absent in other primates living in such populations.
Perhaps the rapid enlargement of the human brain in evolutionary history furnished new and more effective survival strategies, while reproductive lifespan has simply not had the necessary time to catch up. I'm highly sceptical of the frequent suggestions that menopause is some kind of adaptation.
today one would be tempted to say that the offspring of human parents that die when still fertile is in turn less likely to reproduce as misses parents' financial help (or other kind of help, like grandmas that grow up kids in lieu of their sons or daughters)... More seriously, is it possible that social relationships more complex than in other species privilege who can coexist longer with his/her ancestors?