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Menstrual Cycles Continue into Advanced Old Age in the Common Chimpanzee (Pan troglodytes)¹

Department of Psychology,³ University of Massachusetts, Amherst, Massachusetts 01003 Yerkes National Primate Research Center,⁴ Emory University, Atlanta, Georgia 30322 Department of Anthropology,⁵ University of Utah, Salt Lake City, Utah 84112 Department of Biostatistics and Bioinformatics,⁶ Rollins School of Public Health, Emory University, Atlanta, Georgia 30322

ABSTRACT

A long postreproductive lifespan may distinguish women from all other female primates. A long-held consensus among reproductive scientists has been that our closest living relative, the chimpanzee (Pan troglodytes), experiences menstrual cycles until death. However, a recent study of biannual assessments of gonadotropins, but lacking observations of menstruation, concluded that menopause occurs in chimpanzees between 35 and 40 yr of age. A separate report, but on wild chimpanzees, documented fertility through the 40–44 age range in all populations studied. These contradictory reports pose questions about differences between wild and captive populations and about assessments of menopause. The present study revisits this controversy by analyzing longitudinal records of anogenital swelling and menstruation in 89 female chimpanzees aged 6 to 59 yr (n = 2386 records on cycle length), monitored for most of their adult lives at the Yerkes National Primate Research Center. Twenty of these chimpanzees were observed past 39 yr of age; all 20 displayed menstrual cycles beyond this age, as confirmed by at least two observations of menses about 35 days apart. Three of these were older than 50 yr and still displayed menstrual cycles. Only the oldest female appeared menopausal, with cycles of anogenital swelling ceasing 2 yr prior to her death at age 59. Random-effects statistical modeling reveals a slight decrease in cycle length until 20 yr of age and a slight lengthening thereafter. Mean cycle length across the lifespan is 35.4 days. Our findings, based upon actual observations of menstrual cycles, suggest that menopause in the chimpanzee is rare, occurring near the end of the lifespan.

aging, evolution, life history, longevity, longitudinal analysis, menopause, menstrual cycle, menstruation, ovulatory cycle, reproduction, sexual swelling

¹ Supported by National Institutes of Health grants P51RR000165 and P01AG026423.

Correspondence: ²James G. Herndon, Division of Neuroscience, Yerkes National Primate Research Center, Emory University, Atlanta, GA 30322. FAX: 404 727 3278; e-mail: jim{at}rmy.emory.edu

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