Abstract
Menopause in women occurs at mid-life. Chimpanzees, in contrast, continue to display cycles of menstrual bleeding and genital swelling, suggestive of ovulation, until near their maximum life span of about 60 years. Because ovulation was not confirmed hormonally, however, the age at which chimpanzees experience menopause has remained uncertain. In the present study, we provide hormonal data from urine samples collected from 30 female chimpanzees, of which 9 were old (>30 years), including 2 above the age of 50 years. Eight old chimpanzees showed clear endocrine evidence of ovulation, as well as cycles of genital swelling that correlated closely with measured endocrine changes. Endocrine evidence thus confirms prior observations (cyclic anogenital swelling) that menopause is a late-life event in the chimpanzee. We also unexpectedly discovered an idiopathic anovulation in some young and middle-aged chimpanzees; this merits further study. Because our results on old chimpanzees validate the use of anogenital swelling as a surrogate index of ovulation, we were able to combine data on swelling and urinary hormones to provide the first estimates of age-specific rates of menopause in chimpanzees. We conclude that menopause occurs near 50 years of age in chimpanzees as it does in women. Our finding identifies a basic difference between the human and chimpanzee aging processes: female chimpanzees can remain reproductively viable for a greater proportion of their life span than women. Thus, while menopause marks the end of the chimpanzee's life span, women may thrive for decades more.