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According to a new analysis of an aggregate set of genealogical trees of more than 400 million people, genetics has far less influence on the length of life than the one we thought before. The results suggest that the heritability of life span is well below previous estimates, which has not allowed us to explain our tendency to select partners with traits similar to ours. The research, from Calico Life Sciences and Ancestry, was published in GENETIC, review of the Genetics Society of America.
"We can potentially learn a lot about the biology of aging through human genetics, but if the heritability of life span is low, it changes our expectations about the types of things we can learn and the ease with which they will be learned, "says lead author Graham Rubis. "It helps to contextualize the questions that scientists who study aging can ask effectively."
Calico Life Sciences, Ruby's employer, is a research and development company whose mission is to understand the biology of aging. They teamed up with scientists from the Ancestry Genealogy Online Resource, led by Scientific Lead Catherine Ball, to use genealogical data available on Ancestry.com to estimate the heritability of the lifespan .
Heritability is a measure of the extent to which the variation of a trait, in this case the lifespan, can be explained by genetic differences, as opposed to non-inherited differences. such as lifestyle, socio-cultural factors and accidents. Previous estimates of the heritability of human lifespan ranged from about 15 to 30%.
"The partnership with Ancestry has enabled this new study to have deeper insights by using a much larger dataset than any previous studies on longevity," Ball said.
From 54 million public family trees generated by subscribers representing six billion ancestors, Ancestry has removed the redundant entries and those still alive, by assembling the remaining pedigrees. Before sharing the data with the Calico research team, Ancestry withdrew all identifiable information from family trees, leaving only the year of birth, the year of death, the place of birth ( until the resolution of the US State and countries outside the United States), and the family ties that make up the very structure of the tree.
They resulted in a set of family trees with more than 400 million people, mostly European Americans, connected to each other through a parent-child or spouse relationship. The team was then able to estimate heritability from the tree by examining the similarity of the lifespan between parents.
Using a combination of mathematical and statistical modeling, researchers focused on family members born in the 19th and early 20th centuries. But, as has also been observed in some of the previous studies, they noted that spouses' longevity tended to be correlated – they were actually more similar than siblings of the opposite sex.
This correlation between spouses may be due to the many non-genetic factors that accompany life in the same household – their shared environment. But the story really began to take shape when the authors compared different types of in-laws, some of whom had rather distant relationships.
The first clue that something more than genetics or the shared environment might be at work was the discovery that brothers-in-law and cousins had a correlated lifespan – although They are not blood relatives and usually do not share households.
The size of their dataset allowed the team to focus on longevity correlations for other, more distant types of relationships, including aunts and uncles, first cousins a once removed, and the different configurations of co-brothers and sisters. -law. The finding that the sibling's brother or their spouse's spouse had a life span similar to theirs made it clear that there was something else at stake.
If they do not share their genetic background and their households, what is the best explanation for the similarity of life span between individuals with these types of relationships? To return to their impressive dataset, the researchers were able to perform analyzes to detect matching matches.
"What mating associates means here is that life-long factors tend to be very similar between partners," says Ruby. In other words, people tend to choose partners with traits like theirs – in this case, how long do they live.
Of course, you can not easily guess the longevity of a potential partner. "Usually, people get married before the death of one or the other," jokes Ruby. Because you can not tell the life of someone in advance, the assortative mating in humans must be based on other characteristics.
The basis of this choice of partner may be genetic or socio-cultural, or both. For a non-genetic example, if income influences the length of life and wealthy people tend to marry other rich people, this would lead to a correlated longevity. The same thing would happen for traits more controlled by genetics: if, for example, tall people preferred larger spouses, and size was correlated in one way or another with your life, this would also increase the estimates of heritability in the long run.
In correcting for these effects of assortative mating, the new analysis showed that heritability over life span was probably not more than 7%, or even less.
The result? The length of your life depends less on your genes than you think.
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