• We used to think that genetics accounted for some 15-30 percent of life expectancy
• Genes do influence our risks of many health concerns and disease like cancer
• But a new study of Ancestry.com family tree data on 400 million people shows that lifespan is less inherited than we thought
• Scientists at the Genetics Society of America believe that lifespans that ‘run in families’ are largely seen because we choose partners similar to us
• Now, they estimate DNA accounts for only about seven percent of lifespan

Your genes have little to do with how long you will live, according to a new ‘family tree’ study of more than 400 million people.

DNA determines many of our traits, and as genetic analysis becomes better and more accessible, it’s tempting to think it can predict our health – and what we will pass on to future generations.

However, longevity is influenced as much – if not more – by environmental factors, like your diet and whether or not you smoke, as well as social factors such as wealth that is even harder to factor into the equation.

But, as the study from research company Calico Life Sciences and Ancestry.com show, our familial relationships inject much greater uncertainty into the DNA equation.

And while long lives do run in families, we can hardly count on our parents’ longevity to predict our own.

Image: Lifespans do tend to run in families – but its more because we pick mates that are similar to ourselves than it is due to genetics, according to a new family tree study of 400 million people

In fact, only about seven percent of our lifespan is based on our genetics, the new research reveals.

As animals, we biologically want to survive as long as possible.

And it’s in human nature to look for patterns to emulate in those who live longest.

Gerontology is an entire subset of science dedicated to studying aging and everything that determines it.

For some scientists, the study of the longest living people borders on obsession as they chase the dream of immortality.

Unsurprisingly, they covet the genetic profiles and life stories of people like Jean Calment, a French woman who holds the record for the longest life ever recorded. She died in 1997, at the age of 122.

She has been called ‘almost immortal,’ and its true that she wasn’t the only one from her family to break the genetic mold: her father died just before his 93rd birthday, her mother died at 86, and her brother lived to be 97.

But her children did not inherit those ‘good genes,’ as we are wont to say. Or, if they did, those genetics didn’t protect them from other variables.

Jeanne’s daughter, Yvonne, died at 35 of pneumonia and her son, Frederic, died at 73 after eating spoiled cherries. Her grandson (also Frederic) died at 36, in a car crash. Her husband, Fernand, died in 1942, at 74.

In the past, scientists believed that between 15 and 30 percent of Yvonne and Frederic’s potential lifespans would have depended on Jeanne and Fernand.

But there is now more family tree and genetic data available for analysis than ever, and GSA’s research shows that our genes have far less to do with longevity than we thought.

The researchers used data from Ancestry.com’s database of 54 million family trees. Altogether, those trees had connected people to six billion ancestors.

Once the redundancies and mistakes were cut out of those trees, the scientists had a set of 400 million people, although the majority were Americans or descended from Europeans, meaning the sample was predominantly white.

Like Jeanne’s family, siblings tended to have similar life expectancies, as did cousins.

But those blood-relatives did not have the most similar life spans.

It turned out that spouses were more likely to live about as long as one another than were siblings of the opposite sex. Even in-laws tended to have similar live spans.

These genetically inexplicable patterns raised the scientists’ suspicions, but they narrowed their explanation down to something called ‘assortative mating.’

‘What assortative mating means here is that the factors that are important for lifespan tend to be very similar between mate,’ explained lead study author Dr Graham Ruby of Calico Life Sciences research company.

Essentially, we like ourselves – and we tend to pick partners that are like ourselves.

‘Generally, people get married before either one of them has died,’ Dr. Ruby jokes.

‘Because you can’t tell someone’s lifespan in advance, assortative mating in humans must be based on other characteristics.’

Those characteristics may include inherited physical traits, or factors like wealth, or other social or cultural commonalities that may also influence lifespan (people of similar heights tend to have similar lifespans, but so do people with similar incomes).

Our own families (and all their shared genetic and environmental traits) influence whom we choose as a mate as well.

This may help to explain our tendency to pick partners like ourselves, though perhaps on a subconscious level, as we search out someone aligned with our own values, and whom feels familiar.

So, these may be a series of correlations in gene pools that don’t prove causation – that longevity is actually passed down through DNA.

Once these other traits, which are shared among families, but are not necessarily genetic, pure DNA could only be credited for about seven percent of longevity.

‘We can potentially learn many things about the biology of aging from human genetics, but if the heritability of lifespan is low, it tempers our expectations about what types of things we can learn and how easy it will be,’ said Dr. Ruby.