Menopause has been defined as an evolutionary oddity: it occurs only in six species of mammals out of over 6,000 and we humans are the only earthlings to have developed a long post-reproductive life in natural conditions. This is because in the animal world, in general, females tend to reproduce throughout their adult lives, thus maximizing the chances of survival of the species, while human women physiologically stop reproduction several decades before the end of their lives. And we don’t know exactly why. Now a new study on whales provides some clues.
Understanding the evolution of menopause
Understanding how and why menopause evolved is a long-standing challenge across mammals. The most studied theories to date suggest that menopause in humans evolved due to a combination of benefits, from less competition for resources to genetic damage due to aging. Now the study conducted by the Center for Animal Behavior Research at the University of Exeter, published on Naturereveals for the first time the benefits of menopause among orcas and whales, revealing that this phase of quiescence is closely related to the life expectancy and survival of the entire family group.
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A prolonged lifespan increases opportunities for female whales to help their sons and grandsons without generating competition with their daughters. “When mothers and daughters reproduce at the same time, there is a potential conflict over resources because both will want to give priority to their offspring. By stopping to reproduce, however, females minimize this problem,” explains the professor Darren Croftbehavioral ecologist at the University of Exeter and director of the Center for Whale Research in Washington.
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The support of grandmothers
“This result provides an alternative view of how menopause evolved – adds the professor Sam Ellis, expert in animal behavior, lead author of the study – . Menopausal whale species have a similar reproductive period as non-menopausal species. It’s life after reproduction that differs. Evolution has selected for a longer female lifespan so that mothers and grandmothers can continue to provide support for their family even after reproduction. In the water we see exactly the same patterns in human societies where orcas and female whales have a reproductive period similar to that of our closest primate relatives, but a much longer total lifespan.” In short, a secret of long life and prosperity.
The whales
Pacific whales that go through menopause stop reproducing around age 40, but then live into their 60s, and some even reach 80, while males typically die before 40. And grandmothers help their daughters and their grandchildren providing food, protection and wisdom. “We found that puppies with a living menopausal grandmother had better survival than those without,” confirms Professor Ellis.
“In years when resources are scarce, older females lead their group, suggesting a role of ecological knowledge that allows them to survive. We also found that older females catch fish but only eat half of them, to share the remaining part with other family members. A behavior much less common in younger females and almost non-existent in males.”
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Female reproduction
It must be said that menopause evolved independently in humans and whales, whose last common ancestor dates back to about 90 million years ago. “From an evolutionary perspective, life after reproduction is difficult to explain. For most species, evolution favors the reproduction of females until the end of their lives to maximize the transmission of their genes to future generations,” he concludes Professor Croft. “But then why did menopause evolve in humans and toothed whales? The key to this is the opportunity to help relatives survive.” A way to look at the survival of the species with different eyes, including greater care, nurturing and commitment to the education of a child, which goes far beyond the simple concept of the birth rate decline.
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– 2024-03-15 17:09:06
