A new study found that a person's DNA has surprisingly little to do with how long they'll live. But here's where researchers did find a surprising connection.

By Amanda MacMillan
November 08, 2018

How long we live seems to have less to do with our genes than previously thought, according to a new study. Yes, our DNA does play something of a role, as does our environment. But scientists also discovered another surprising factor that seems to help determine life expectancy, as well: The person you choose to spend your years with.

The new research, published in the journal Genetics, analyzed the aggregated family tress of more than 400 million people. The data—including people’s year of birth, year of death, place of birth, and familial connections—was provided by Ancestry, after the genealogy company stripped away any identifiable information from its subscribers. The people in these family trees were largely of American and European descent, born in either the 1800s or early 1900s.

With this information, researchers were able to estimate to what extent a person’s lifespan was passed down from his or her parents and how much was influenced by other factors like environment, socioeconomic issues, or tragic accidents, for example. (You know, the whole nature versus nurture debate.)

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It’s been previously thought that the heritability of human lifespan—a measure of how much our genes play a role—is about 15 to 30%. And when researchers examined the similarity of lifespan between siblings and first cousins, they found that to be about accurate.

However, they also found that the lifespan of male-female spouses in their study tended to be more closely correlated than the lifespan of male-female siblings—suggesting that who we marry matters even more to our longevity than who our biological family is. Part of that is surely due to spouses living in a similar environment, the authors acknowledge, but it also seems to be more complicated than that.

That’s because the study also looked at pairs of siblings-in-law and first-cousins-in-law and found that these people also had similar lifespans, despite not being blood relatives and typically not sharing households. Even people’s aunts- or uncles-in-law seemed to have some influence on their lifespan.

So how, exactly, does your spouse’s sibling, or your spouse’s sibling’s spouse, affect your own longevity? The researchers say it has to do with something they call assortative mating.

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"What assortative mating means here is that the factors that are important for lifespan tend to be very similar between mates," said Graham Ruby, PhD, a researcher at Calico Life Sciences, in a press release. In other words, people tend to select partners with traits like their own—traits they also tend to share with their biological families.

Those traits, then, influence how long people live. And if people marry into families that mirror their own, it makes sense that people related only by marriage would have similar lifespans—even if they’re separated by a few degrees.

Many of those traits have nothing to do with our DNA: Wealthy people may tend to marry other wealthy people, for example, and their economic status may also help them live longer. But some of them likely do have a genetic basis—like if tall people tend to marry other tall people. (The effect of height on lifespan isn’t entirely clear, but it has been linked to several aspects of health and wellness.)

The authors say that those previous estimates about heritability didn’t take this type of assortative mating into account, which inflated the suspected influence of genetics alone. When they analyzed the family trees again and corrected for the effects of like-marrying-like, they found that lifespan heritability is likely no more than 7%, or perhaps even lower.

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To be clear, it’s not like we’re going on dates and evaluating potential partners based on their life expectancy—which isn’t really something we can easily tell, anyway. Most of this happens subconsciously, and of course there are always exceptions.

What this study means to science, the authors say, is that research on longevity and the genes behind healthy aging might be much more limited—and become much more difficult—than previously suspected.

What it means to us, on the other hand, is that good or bad genes don’t dictate our futures. Having long-living relatives won’t necessarily protect us from an early demise, just as having family who died young won’t doom us to a similar fate.

“Right now a healthy lifespan looks to be more of a function of the choices that we make,” Ancestry’s chief scientific officer Catherine Bell told Wired. For example, she says, lifespan dipped significantly during World War I and around the time people took up cigarette smoking.

“Don’t smoke, and don’t go to war,” she said. “Those are my two pieces of advice.” Research also suggests that other healthy behaviors—like maintaining a normal weight and moderating alcohol consumption—can help you add years to your life (and life to your years), as well.

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