Menopause explains why some whales live so long

menopause It is a period that very few mammals have, including some toothed whales in which it may have evolved so that females live longer and help younger generations survive without competing with daughters or granddaughters for reproductive partners.

Women and five types of toothed whales, beluga, narwhal, pilot whale, orca and black killer whale, are the only mammals known to go through menopause, apart from a specific community of wild chimpanzees in Uganda.

Females of these whale species live about 40 years longer than others of a similar size, according to a study published today by Nature led by the University of Exeter (United Kingdom).

The extension of life expectancy may be due to “intergenerational benefits, to the help that older females can give to younger relatives”and the reason for not extending the reproductive life is to avoid entering into competition with the daughters, explained Samuel Ellis, the first signatory of the research, in a virtual press conference.

Additionally, females outlive males of their own species. In the case of orcas, they can live up to 80 years old, while they usually die around 40.

The research provides evidence that menopause evolved by extending the lifespan of females beyond their reproductive years, rather than by reducing their reproductive lifespan.

Similarities with human menopause

The question of why menopause has evolved is “absolutely fascinating and it is quite surprising that among more than 5,000 species of mammals we see this trait in only a handful of species”highlighted researcher Darren Croft, from the University of Exeter, at the press conference.

The results of the study show that the evolution of menopause in toothed whales has a “striking similarity” with that of humans, through a longer lifespan without simultaneously extending the reproductive period.

“It is the same life history pattern that we have seen in humans. “It is absolutely amazing that we can make these comparisons with such a different group of animals.” and from which 90 million years of evolution separate us

This study is “really solid evidence” -he added- that menopause is an adaptation that has evolved due to the benefits that, in these cases, females can provide their family beyond their reproductive period.

In the case of the five species of toothed whales studied, all have a “unusual social structure”a type of matriarchy where females spend their lives in close contact with their offspring and grandchildren.

They help survival

Thus, they have the opportunity to help improve the family’s chance of survival. The researcher pointed out that, from previous work by his group, it is known that females of post-reproductive age store knowledge about when and where to find food.

The experience they acquire throughout their lives “It is really crucial to address environmental challenges in times of difficulty”. They also share their own food with the younger ones, act as ‘babysitters’ and protect their male offspring.

Continuing with the parallel with humans, Croft pointed out that the same patterns were seen in hunter-gatherer societies. In times of drought or social conflict, people turned to the elders of their community, who had experience and knowledge.

Menopause increases the vital overlap between whales and their offspring, but since they do not reproduce at the same time as their daughters and granddaughters, they avoid that type of competition, which has a cost.

In the orca populations they have worked with, Croft said, they have seen that when mothers and daughters try to reproduce at the same time, the older females’ calves have lower survival.

Menopause, the study suggests, evolves when there are benefits for the species and despite the obvious differences between whales and humans, its convergent evolution offers new perspectives for understanding the evolution of menopause in general.

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