Chimps Challenge Previous Assumptions About Menopause Female chimpanzees in an East African forest not only go through menopause but continue to thrive for years, even decades, after their reproductive capabilities cease. This novel observation defies previous beliefs which limited post-reproductive longevity to humans and certain whale species.
Redefining Evolutionary Narratives The discovery, presented by UCLA evolutionary anthropologist Brian Wood in the Oct. 27 issue of Science, brings forth intriguing questions on the evolutionary purpose of menopause. Historically, menopause’s evolutionary advantage has remained elusive since it ostensibly counters the principle of passing on one’s genes. However, Wood highlights that this newfound evidence underscores the profound genetic similarities between humans and chimpanzees, suggesting an inherent predisposition towards longevity after reproductive years in both species.
Contrasting Observations in Chimpanzee Longevity Anthropologist Kristen Hawkes from the University of Utah, Salt Lake City, points out that in some studies, including Jane Goodall’s renowned research on chimps at Tanzania’s Gombe National Park, female chimpanzees usually aged rapidly, often passing away in their early 30s while still menstruating. Hence, Wood’s observation of numerous female chimps surviving well past menopause comes as a significant revelation.
A Closer Look at the Ngogo Chimps Wood’s team meticulously studied the Ngogo community of wild chimps in Uganda’s Kibale National Park from 1995 to 2016, focusing on the mortality and fertility rates of 185 females. Initial observations were made on younger and middle-aged chimps, ensuring accurate age assessments.
Fertility markers began to drop post the age of 30, with no recorded births in chimps aged over 50. Out of the observed group, 16 female chimps lived beyond 50, some even reaching their 60s. Moreover, urine samples from 66 females (aged 14 to 67) reflected a noticeable decline in fertility after 30, leading to a complete cessation by around 50 – an age parallel to when human females typically experience menopause.
Post-Menopausal Life in Chimps In the studied Ngogo community, females spent an average of 20% of their adult lives, starting from age 14, in a post-reproductive phase, a pattern not previously attributed to non-human primates in the wild.
This pivotal study reopens discussions about the evolutionary reasons behind menopause and highlights the need to expand our understanding of life stages in our closest genetic relatives.