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Romantic scenes that never happen: your eyes meet. Your heart is pounding. This is the person you are sure of, because you are convinced that she will live to 95 years. That's what you've always dreamed of.
Lifespan is not usually on the list of people looking for what they are looking for in a partner. But, according to an article published this week in the journal Genetics longevity is closely related to marital relationships, which means that people quite well choose partners who live similar lives. Having ignored this behavior, estimates of the genetic contribution to longevity have been significantly overestimated.
I knew the second time I saw your blood
Nobody chooses partners based on the length of their lives. As the authors of the document wisely note, life expectancy "can not be observed until death, when the opportunity to marry is over." But as anyone who has ever been outside can tell you, people are likely to marry their partner (or close to it). ) in such characteristics as wealth and education, which play an obvious role in longevity.
J. Graham Ruby, the lead author of the paper, works for Calico Life Sciences, a research and development company founded by Alphabet. Calico's mission is to harness advanced technologies to better understand the biology that controls lifespan. Ruby has used huge amounts of data from Ancestry.com to study the role of genes in the lives of more than 400,000 people born in the 1800s and beyond. early 20th century
When it comes to complex traits like lifespan, a large number of genes will play a role, as will a myriad of environmental factors. The role of genes is therefore described according to the variability that it can explain. Estimates of genetic influence vary between 15 and 30%, which means that genetic differences between individuals can account for up to 30% of the observed variation in the length of life.
Estimates vary in part because of differences in data and calculation sources. methods and partly because the statistics will not be the same from one population to another: countries differ in the most common causes of death, the environmental risk factors that people face and the the extent to which different people are exposed to the same risk factors. For example, in a poor country where the risk of contracting an infectious disease and dying in childbirth is high, the few wealthy citizens can avoid these risks through expensive health care. This will be very different from a rich and egalitarian country where cancer is one of the leading causes of death.
Your life is correlated with that of your brother-in-law
The calculations are complicated, but the thinking behind them is simple: When genes play a role in a trait, you should be pretty similar to your brothers and sisters and your parents, a little less like your cousins, less like your secondary cousins, & c. Ruby and his colleagues used the family tree data to determine if life spans were similar between close and close relatives. This produced heritability estimates similar to those previously calculated: the life span of siblings was strongly correlated, the first cousins a little less correlated, and so on.
But the life of the spouses was also correlated. This could be easily explained by spouses sharing the same household and lifestyle: eating the same healthy diet or eating cigarettes together. But researchers have noticed something odd: the lifespan of other relatives related solely by marriage has also been correlated. This can not be explained by genes or a shared environment.
Ruby and his colleagues began to study the life of the in-laws. They then studied first-time siblings, then more distant relationships, such as "the brother or sister of a brother's spouse" (the sister of your brother's wife) and "the spouse of a brother". A brother or sister of a spouse "(the husband of your husband's sister). Even in these distant relationships, the life span was correlated: if your spouse's spouse, brother or sister, has reached advanced age, this means that you are a little more likely to do the same.
What happens here is an badortative marriage: it is likely that people marry people who match them on certain characteristics, such as education and wealth, and these characteristics are in turn related to the longevity. This high level of badortative mating has greatly inflated the estimate of heritability. Once this has been taken into account, Ruby and his colleagues have achieved a much lower genetic influence figure of 7%, at most. These seven percent include both genetics and inherited non-genetic traits, such as healthy or unhealthy habits that parents pbad on to their children. These two things can be tricky to separate, but it's fair to badume that the contribution of genetics is even lower.
This is an estimate that may change, and has already probably already done so, as this study was based on a set of historical data from people. born in very different health landscapes and very different marital practices. The Ancestry.com database also contains a very large amount of data on American families of European origin, which limits the generalization to other groups, countries, cultures and eras. But this is an essential observation for thinking about heritability statistics in general, because badortative mating covers all kinds of characteristics. It must also be taken into account that negative opposing badociations, also known as attract contraries, attract attention.
This may seem disappointing for a company interested in "life-sustaining biology". But, of course, the disease remains biological, even though the causes of these processes are less present in our genes than previously thought. In fact, looking for what constitutes the vast majority of differences in the life span of people can be precisely what gives the most interesting answers.
Genetics 2018. DOI: 10.1534 / genetics.118.301613 (About DOIs)
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