Researchers Use Killer Whales as Models for Studying the Evolution of Menopause

Scientists may have just solved the mystery of menopause. Older female killer whales stop reproducing to avoid competing with their daughters. Instead, they invest resources into taking care of relatives. The findings are in a paper that was just published in the journal Current Biology.

Menopause is extremely rare in the animal kingdom and humans are one of the only species to undergo the process. It’s a bit of an evolutionary puzzle—it doesn’t make much sense for females to lose the ability to reproduce when they’re still healthy and can live decades longer. In other animal species, females can continue to have offspring until very old age or death. Interestingly, menopause is something that humans have in common with killer whales (Orcinus orca). Killer whales, also known as orcas, undergo menopause just like humans. Scientists aren’t completely sure why menopause exists in some animal species.

A team of researchers from the University of Exeter used data from Fisheries and Oceans Canada and the Center for Whale Research. The organizations’ joint database includes information on wild killer whales that have been tracked for over 45 years. The research team analyzed the data to see if a recent theory held true. Some scientists have theorized that menopause exists to prevent mothers from competing with their daughters. The idea is that older females are already less suited to raising offspring and may not have the energy to compete with their young daughters. Instead, they might be better off avoiding reproductive conflict to support their relatives.

The researchers found that the offspring of older female killer whales were 1.7 times more likely to die when compared to the offspring of younger whales. As a female killer whale ages, she’s also likely to live with more relatives, including her daughters and granddaughters. Most killer whales stay with their pod for life and the oldest females lead the group. Instead of wasting energy trying to compete with her own relatives, it makes more sense for an older female to help her adult offspring and relatives. This makes it more likely that her genes, which she shares with her family, will be passed down. Menopause removes any possible reproductive conflicts, allowing the older whales to dedicate themselves to helping their family.

As a female killer whale ages, she might be better off helping her family members instead of reproducing. Menopause eliminates any reproductive conflict, which would generally favor the younger females. The findings may help explain how menopause evolved in certain animals, including humans.

REFERENCE

Croft et al. Reproductive Conflict and the Evolution of Menopause in Killer Whales. Current Biology (2017).

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