Dr. Vince Gutschick explores life after fertility in chimps.
Menopause in humans is a troublesome time for the women undergoing it. At the same time, it gives us older people more time to contribute to the care of infants, like grandchildren, among other things. This benefit to related individuals continues for years – up to half the lifetime of the “granny” in humans, almost as long in some whales.
An argument called kin selection may explain why lifespan after reproduction evolved.
No other primates (apes, monkeys, lemurs, etc.) showed this pattern, with females living after ending reproduction until now. Some female members of the Ngogo chimpanzees in Uganda’s Kibale National Park live long past reproductive age. How do we know that? It took decades of visual observation of the individuals and monitoring of hormone levels found in urine.
Brian Wood and 8 colleagues argue that kin selection isn’t the reason that lifespan after reproduction evolved. They note that lifespan of most chimpanzees has likely been underestimated because we humans kill or displace them; only the Ngogo population lived long enough to exhibit menopause. Also, kin selection works if the females stay with the same troop and if they care for grand”children.” Old Ngogo females seem to provide group knowledge rather than care. They may also stop reproducing to avoid competing with young females. So, there may be two reasons for menopause, differing in humans, chimpanzees, and whales.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
