Living things are usually programmed to live to their age of maximum sexual maturity and then die out once they are no longer fertile. However, humans live well beyond this theoretical age. In the 1960s, researchers therefore put forward the “grandmother hypothesis”, which explains that the help of grandmothers allows mothers to have more children, and thus pass their longevity genes. . A hypothesis reinforced today by the explanation of the physical activity of seniors.
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[EN VIDÉO] Interview: what are the secrets of longevity? Living things have a limited lifespan and research is beginning to understand what mechanisms are involved. But would knowing these secrets lead to a longer life? Futura-Sciences interviewed Biology Researcher Vera Gorbunova during her talk at TEDxCannes to find out more.
Living things are generally genetically programmed for a duration of life corresponding to the end of their reproductive age. Because beyond this age, the elderly are considered “useless” and no longer provide any benefit for the survival of thespecies. However, it is observed in humans that a third of the average lifespan of women is postmenopause. Apart from certain species of cetaceans or sharks, this longevity is exceptional in the animal kingdom.
The grandmother hypothesis, an idea that emerged in the 1960s
In the 1960s, the “grandmother hypothesis” emerged, postulating that female longevity is explained by the gain in reproductive terms of longer life in women. The first evidence for this theory was gathered by Kristen Hawkes, an anthropologist at the University of Utah who studied the Hadza people, a group of hunter-gatherers from northern Tanzania. Hawkes had been struck by the “productivity” of these old ladies who went out in search of food, and later documented how their help enabled mothers to have more children. Numerous studies have subsequently supported this “grandmother effect” using ethnographic, historical and sociological data. In 2019, a study focusing on populations in Quebec and Finland in the pre-industrial years shows, for example, the beneficial effects of grandmothers, with a drop in infant mortality and an earlier reproductive age among women living near their own mother.
Grandmothers’ physical activity would protect them from senescence
A new study published in December 2021 in the journal PNAS and led by Daniel Lieberman, a professor at Harvard University, makes a further argument in favor of the grandmother hypothesis. According to the researcher, the maintaining physical activity in the later stages of life slows down the process of senescence, which protects against chronic disorders and aging. ” There is thus an evolutionary selection favored by physical activity », Attests Daniel Lieberman in an interview with the magazine Scientific American. The activity physical reduces fat storage and produces molecules anti-oxidatives to slow down the natural senescence of cells.
But if this hypothesis is true, then why do women not live even longer, in order to help their great-grandchildren? According to Simon Chapam, who conducted the 2019 study, grandmother’s help declines as grandchildren get older, and her “reproductive value” therefore declines as a result. The researcher found that the death rates of grandmothers are increasing just as their abilities are declining. After a while it’s just too many mouths to feed, estimates Simon Chapam.
A hypothesis that is not unanimous
This hypothesis of the grandmother is however still debated. In 2019, researchers calculated that the longevity “Natural” to humans was 38 years old, based on the rate of senescence of DNA. But, according to the researchers, the abnormally long lifespan we know is more linked to the progress of medicine. Moreover, our lifestyle, which is more sedentary than that of our hunter-gatherer ancestors, should have led to a reduction in our life expectancy according to Lieberman’s principle. Finally, the grandmother’s hypothesis provides no explanation for the fact that spermatogenesis in men continues well beyond women’s menopause age.
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