Lifespan has little to do with genes, ancestry database analysis shows

MMillions of amateur genealogists assembling family trees on Ancestry.com probably think they are only tracking lost relatives and assessing their genetic proximity to Prince Harry, but in fact, they have unwittingly made a significant contribution to science. An analysis of the website’s 54 million public family trees reveals that lifespan heritability, a hot topic of research for decades, is considerably less than commonly thought.

Scientists reported on Tuesday that genes make up well under 7 percent of people’s lifespans, up from 20 to 30 percent of most previous estimates.

This low heritability “implies that it would be more difficult” to affect lifespan through genetic tinkering or other life extension ideas, said computational geneticist J. Graham Ruby of Calico Life Sciences, lead author of study published in the journal Genetics. Google founded Calico in 2013 to find ways to fight aging.

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Researchers studying the contributions of genes and the environment to health have not been surprised by the low heritability. “Welcome aboard!” said Dr Sandro Galea, dean of the Boston University School of Public Health, who studied the limits genetic influences on complex outcomes like lifespan. “As long as you accept that genetic factors coexist with environmental factors, it limits the influence that genetics can have.”

Calico and Ancestry researchers analyzed 54.43 million family trees, amassing the birth and death dates of 406 million people (all anonymized, so no personal data has been revealed) born between the 19th century. century and the mid-twentieth century. Most people born more recently are still alive, their lifespan to be determined.

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The researchers calculated the correlations of the lifespans of spouses and parent-child couples, siblings and first cousins, and more distant couples such as a person and his or her spouse’s sibling or partner. spouse of his brother or sister.

The first indication that genes were not the dominant influence came from the lifespan of spouses: they were more similar than the lifespans of sisters and brothers. Since spouses share relatively few DNA variants, this suggests a strong influence of non-genetic factors they share, such as living away from epidemics, having access to clean water, being literate, eating healthy foods. and not to smoke.

Even more striking were the high correlations between the lifespans of relatives even more distant by marriage and not by blood, such as step-siblings, step-cousins, step-aunts, and step-brothers. -uncles, and first cousins-in-law once removed. If a person has lived to old age or died young, the brother or sister of his or her brother’s or sister’s spouse, the spouse of his or her spouse’s brother or sister or another distant step-parent.

“As we got closer to increasingly distant relatives, the correlations didn’t go down as much” as they should have been if genes determined lifespan, “Ruby said. One way to explain this, along with the strong correlation between the lifespan of in-laws, is whether people choose spouses with whom they share traits that are important for lifespan. If income increases lifespan (it does) and 1 percent marries other 1 percent (especially in times analyzed by scientists), then spousal lifespan would be strongly correlated for that. reason, as is the lifespan of the in-laws.

“You are more likely to have a lifespan similar to that of your in-laws than an equally independent stranger,” said Catherine Ball, Ancestry Scientific Director and lead author of the study. In addition, by choosing partners like them, people are actually giving their children double doses of factors that affect lifespan but are not genetic, such as attitudes towards risk-taking or risk-taking. alcohol consumption.

It’s rare “for a teetotaler to marry a party girl or an ultra-marathon runner to marry a couch potato,” she said.

These hundreds of millions of birth and death dates allow researchers at Calico and Ancestry to calculate that factors passed down from generation to generation account for 7% of the difference between a person’s lifespan and that of a person. other. The genetic contribution, however, is even smaller: in addition to genes, people in the United States and other low (and declining) societies economic mobility also inherit non-genetic contributions to life span such as education, income, access to health care and other socio-cultural influences.

The discovery that the heritability of lifespan from factors of all kinds does not exceed 7% means that genes explain even less (but it still pays to choose one’s parents, due to the non-genetic inheritance of lifetime).

“This is a very good job demonstrating once again the power of crowdsourced genealogy,” said computational biologist Yaniv Erlich, who took a leave of absence from Columbia University last year to become scientific director. from the MyHeritage genealogy site. “I also congratulate the authors for their scientific integrity. Most of them work in a company that is trying to understand the genetics of longevity, and they basically claim that the heritability of longevity is really low.

Ancestry’s family trees contain the largest set of data ever analyzed in a lifespan study, but smaller analyzes also reduced the estimate of its heritability, by 20% or more in the 1990s. A 2011 study of alpine populations reached 15 percent, and a 2018 study of family trees on the genealogy site Geni.com, run by Erlich, reached 15 percent.

Although genes seem to have only a small influence on lifespan, they may play a bigger role in determining whether a person lives to old age. Research on centenarians has reported a strong influence of genes, identify a few dozen variants that are particularly common among those who live to 100 years.

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