This project will monitor physiological changes with age in captive female chimpanzees and compare them with those reported for women. Comparisons include ovarian follicle counts, menstrual cycle periodicity, telomere lengths, adrenal steroid characteristics, and muscle strength. All measurements will be minimally invasive or postmortem (following deaths unrelated to this project).
Chimpanzees are the living species phylogenetically closest and most genetically like humans. Their life histories are broadly similar; yet differ in key details, notably the duration of adult life spans. Free-ranging chimpanzees experience high adult mortalities, and rarely live past the age of forty. They are categorized as old while still ovulating. Women on the other hand often live several decades beyond their fertile years and remain vigorous past menopause. This distinct human longevity is not an artifact of recent human history. Though life expectancy at birth has nearly doubled in Western countries since the end of the 19th Century, that increase is largely due to reductions in infant and juvenile mortality. Demographic data for historical populations and for tribal and band communities indicate life expectancies less than forty-five years; nevertheless girls in these populations who survived to adulthood usually outlived their fertility. A third or more of the adult women were past their childbearing years. Comprehensive data on the details of physiological aging in chimpanzees are crucial for an explanation of these differences and the processes involved in the evolution of human longevity.
Quantitative characterization of the aging phenotypes of captive female chimpanzees should be an urgent priority. Systematic measurement of aging physiology is difficult or impossible in the wild. The rearing, housing, and health experience of captives differs from the wild, but medical and social records can be used to assess the effects of these features of captivity. Tissue and record archives allow some measures to be recovered over decades tracking individual heterogeneity in aging trajectories. With the suspension of most captive breeding programs a dozen years ago, the projected size of the next cohort of adults is miniscule. Measuring changes with age on those now moving through adulthood will exploit a disappearing opportunity to clarify and focus evolutionary questions, and also contribute to successful management of the aging captives themselves.
The project involves the collaboration of researchers who normally work with either humans or chimpanzees but not both, so it will promote the synergies needed to accurately characterize the similarities and differences in aging patterns between these two species. Student involvement will be emphasized. In order to reach multiple audiences that can build on project findings, results will be published in journals devoted to research on aging, fertility, primatology, and human evolution. Since data will be recorded on the same individual chimpanzees, co-variation in various physiological systems will contribute to hypotheses about mechanisms that produce similar variation in women.
