Depletion of Ovarian Follicles with Age in Chimpanzees: Similarities to Humans1

Abstract

We retrieved ovarian sections taken from necropsies of 19 captive chimpanzees (Pan troglodytes) aged 0-47 yr, counted the number of primordial follicles in each, and compared the rate of decline in numbers to declines previously documented in humans. The follicular depletion rate in this sample was indistinguishable from that shown across the same ages in classic human data sets. This result supports earlier suggestions that ovarian senescence occurs at the same ages in chimpanzees and humans, implying that the influence of declining ovarian function on other physiologic systems may be distinctively buffered in humans.

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

“…Chimpanzee follicle stocks also vary among individuals of similar age (87). Archived ovarian sections taken at necropsy from captive chimpanzees of ages 0-47 years index this variation and the declining numbers with age (87).…”

“…Archived ovarian sections taken at necropsy from captive chimpanzees of ages 0-47 years index this variation and the declining numbers with age (87). Exponential regressions fit to the age-specific primordial follicle counts on those sections and also to the whole ovary counts across that 0-to 47-year range in the classic human datasets provide a quantitative comparison of follicular loss rate in the two species.…”

Reproductive conflict and the separation of reproductive generations in humans

“…1B). For comparison, there is no indication of an increase in the rate of follicular attrition late in life in chimpanzees (32), rhesus macaques (33), or laboratory rodents (34), the other species for which such data are available. The pattern of attrition in humans, therefore, appears to fit quite well with our hypothesis concerning the timing of intergenerational reproductive conflict.…”

Grandmothering and natural selection

“…Interestingly, our results suggest that, while such a decrease in the mean interbirth interval would not affect longevity, it could have had serious implications for the length of the female reproductive period. The fact that women and female chimps display similar timing in reproductive senescence [2,5] while women start reproducing at a later age [58] implies that the reproductive period in humans may have been shortened from the front end rather than by 'stopping early' (see also [59]). …”

“…But humans are different: women experience total loss of fertility near middle age, often living for decades in a post-menopausal state [3,4], even though it would seem that natural selection should favour those who extend their reproductive period to more closely match their lifespan. For those interested in explaining why women exhibit an exceptionally long postmenopausal lifespan, empirical evidence suggesting that the age of menopause in humans is the ancestral, not derived, condition [2,5] has largely shifted the focus from the evolution of mid-life menopause (e.g. [6]) to the evolution of our distinctively long lifespan (for review, see [7,8]).…”