MENOPAUSE IN FREE-RANGING RHESUS MACAQUES - ESTIMATED INCIDENCE, RELATION TO BODY CONDITION, AND ADAPTIVE SIGNIFICANCE

We examined the question of whether the occurrence of menopause in rhe sus macaque (Macaca mulatta) females approximates that found in women from a life history standpoint. We used data from two provisioned free -ranging populations of rhesus macaques to estimate the probability th at a juvenile female not only will survive to the potentially postmeno pausal age of 25 years but also will cease to experience menstrual cyc les between 25 and 27 years. We used the same data to assess whether a n age-related deterioration in body condition can predict whether fema les greater than or equal to 25 years old will be acyclic. Our analyse s indicate that, within our study populations, (1) less than or equal to 1 in every 10 juvenile females can be expected eventually to underg o the climacteric, and (2) being in poor condition is strongly associa ted with being acyclic in old age. Current theory regarding the evolut ion of senescence in species that do not reproduce by binary fission p osits that aging is a consequence of the force of natural selection de clining with age. Inasmuch as the proportion of female rhesus macaque juveniles that ultimately experience menopause is small and inasmuch a s reproductive senescence does not appear to outpace organismal aging in general (as indexed by an age-related decline in body condition), w e conclude that the occurrence of menopause in rhesus females is parsi moniously explained by the general evolutionary theory of aging and th at the invocation of a special adaptive explanation such as the grandm other hypothesis or a variant thereof, is unnecessary.