In a recent study published in the journal Science, researchers have made a groundbreaking discovery about menopause in chimpanzees. This phenomenon, previously observed primarily in humans and a few species of toothed whales has now been confirmed in the Ngogo community of wild chimpanzees in Uganda’s Kibale National Park. This study sheds new light on the evolution of menopause in primates and its potential underlying mechanisms.

The research team, led by Brian Wood from UCLA, examined data from two decades of observation (1995-2016) of 185 female chimpanzees. They calculated a metric called “postreproductive representation” (PrR), which measures the proportion of an individual’s adult life spent in a post-reproductive state. Surprisingly, the Ngogo chimpanzees exhibited a PrR value of 0.2, indicating that females spent about 20% of their adult years in a post-reproductive state, similar to human menopause.

The findings challenge previous theories about menopause and its evolutionary drivers. While the “grandmother hypothesis” has been commonly used to explain human menopause, where older women support their daughters and grandchildren, this doesn’t apply to chimpanzees, as they do not live near their daughters or provide care for grandchildren. Instead, the study suggests that the extended post-reproductive lifespan in Ngogo chimpanzees might be due to unusually favorable ecological conditions or an evolved, species-typical trait that hasn’t been observed in other populations due to the negative impacts of human activities, particularly disease outbreaks.

This research highlights the importance of studying diverse populations in understanding the evolution of menopause. It raises intriguing questions about the underlying factors in our closest primate relatives contributing to this phenomenon. It also emphasizes the need for long-term field studies to expand our understanding of human biology and behavior.

References

• Cant, M. (2023). Menopause in chimpanzees. Science, 382(6669), 368–369. doi:10.1126/science.adk7119
• Wood, B. M., Negrey, J. D., Brown, J. L., Deschner, T., Thompson, M. E., Gunter, S., … Langergraber, K. E. (n.d.). Demographic and hormonal evidence for menopause in wild chimpanzees. Science, 382(6669), eadd5473. doi:10.1126/science.add5473
• University of California Los Angeles. (2023, October 26). Researchers find first proof of menopause in wild chimpanzees. Phys.Org. https://phys.org/news/2023-10-proof-menopause-wild-chimpanzees.html