Aging and fertility patterns in wild chimpanzees provide insights into the evolution of menopause

Human menopause is remarkable in that reproductive senescence is markedly accelerated relative to somatic aging, leaving an extended postreproductive period for a large proportion of women [1, 2]. Functional explanations for this are debated [3-11], in part because comparative data from closely related species are inadequate. Existing studies of chimpanzees are based on very small samples and have not provided clear conclusions about the reproductive function of aging females [12-19]. These studies have examined whether reproductive senescence in chimpanzees exceeds the pace of general aging, as in humans, or occurs in parallel with declines in overall health, as in many other animals [20, 21]. In order to remedy these problems, we examined fertility and mortality patterns in six free-living chimpanzee populations. Chimpanzee and human birth rates show similar patterns of decline beginning in the fourth decade, suggesting that the physiology of reproductive senescence was relatively conserved in human evolution. However, in contrast to humans, chimpanzee fertility declines are consistent with declines in survivorship, and healthy females maintain high birth rates late into life. Thus, in contrast to recent claims [16], we find no evidence that menopause is a typical characteristic of chimpanzee life histories.