Menopause is a pivotal life change that every woman will experience, so it may surprise you to learn how few other mammals go through menopause.
Until recently, scientists were only aware of menopause in five toothed whale species, though recent research suggests that at least one population of chimpanzees also experiences “the change of life.” All other female mammals appear to retain the ability to have offspring throughout their entire lives.
From an evolutionary standpoint, menopause is puzzling. In the simplest sense, if our purpose is to pass on our genes, a species with female members that live for decades when they can no longer reproduce seems to contradict that biological imperative.
One widely held explanation is that postmenopausal females, in both human and toothed whale social structures, often assist their offspring with raising their young. In other words, they take the job of grandmother very seriously.
A study by University of Exeter researchers, published this month in Nature, appears to support the so-called “grandmother hypothesis” by comparing toothed whales that go through menopause (orcas, narwhals, belugas, false killer whales, and short-finned pilot whales) with the toothed whales (including dolphins and porpoises) that do not.
The scientists noted similar reproductive lifespans across all of the toothed whale species, but those that go through menopause live an average of 40 years longer. By ending their fertile period so many years before the end of their lives, older female whales are no longer in reproductive competition with their female offspring. Thus, they can help ensure the survival of those offspring and assist them in raising their calves.
Whales, chimps, and "the change":
- Other research has found that the grandmotherly role of postmenopausal whales includes sharing food, babysitting, and leading other whales to find fish in times of scarcity. Unlike many other mammals that leave their families when they reach maturity, whales usually live together in groups called pods, often consisting of related individuals, with older females fulfilling matriarchal positions.
- The discovery that some female chimpanzees go through menopause was first reported in October 2023. Researchers found that female chimpanzees in the Ngogo community in western Uganda spend around 20% of their lives beyond their reproductive period, which appears to end around age 50, similar to humans.
- Ngogo is a research site in Kibale National Park, where the chimps live a relatively sheltered life. Unlike many communities, where chimpanzees rarely live beyond age 50, Ngogo chimpanzees often live into their late 60s. However, the grandmother hypothesis doesn’t seem to apply here, as chimpanzee daughters move away from their mothers upon reaching adulthood.
