Aging and Fertility Patterns in Wild Chimpanzees Provide Insights into the Evolution of Menopause

Abstract

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. Functional explanations for this are debated, 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. These studies have not 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. 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, we find no evidence that menopause is a typical characteristic of chimpanzee life histories.

Menopause occurs late in life in the captive chimpanzee (Pan troglodytes)

“…Cheeta ceased cycling at 48 years but was not considered menopausal because at that time she did not meet the criterion of a 12-month interval without menstrual cycles; she has since met this criterion. Our findings on reproductive aging in captivity are entirely consistent with the report that chimpanzees in the wild continue to produce viable offspring throughout the life span, into the 6th decade of life, although fertility declines after about 30 years of age (Emery Thompson et al 2007). Live (Puschmann and Federer 2008), and at a zoo in Manhattan, Kansas, USA (Ross 2009).…”

“…Our observations are consistent with recent data on production of live offspring in older female chimpanzees. For example, although fertility in wild chimpanzees declined steadily through adulthood, they gave birth as late as their 50th year-essentially up until the maximum life span in these populations (Nishida et al 2003;Emery Thompson et al 2007). Captive chimpanzees have also been documented to give birth to healthy infants at the advanced maternal age of 49 (Puschmann and Federer 2008) and 56 years (Ross 2009).…”

Cooperative breeding in South American hunter–gatherers

“…Moreover, female wild chimpanzees show interbirth intervals after surviving offspring that are nearly twice as long as hunter-gatherer women who are subsidized (approx. 70 months for chimpanzees in table 1 of Emery Thompson et al 2007 versus 36 months for Ache in Hill & Hurtado 1996, p. 254). Finally, the cessation of fertility (menopause), when life expectancy is approximately 20 more years (Hill & Hurtado 1996, p. 427), is a hunter-gatherer life-history trait that only makes sense in a cooperative breeding context.…”

How grandmother effects plus individual variation in frailty shape fertility and mortality: Guidance from human–chimpanzee comparisons

“…I focus on two apparent inconsistencies between theoretical expectations and empirical observations. First, theory predicts that current reproductive output should subtract from effort invested in maintenance for survival and reproduction in the future, yet individuals with higher fertility rates tend to continue bearing offspring to older ages; and in humans, women with later last births then survive longer afterward (22)(23)(24)(25). Second, theory predicts that lower adult mortality should slow rates of senescence, yet when populations of the same species are compared, the groups with lower mortality have steeper increases in death risk with advancing age (26,27).…”