Do Your Genes Really Determine Your Life Expectancy?

While it is undeniable that a healthy lifestyle will tend, statistically, to guarantee you age longer, it alone does not do the job. We all have in mind these video archives from the INA, where we can still admire what the average French person was like in the 1960s and 1970s: an unbalanced diet, a good liter of picrate per day accompanied by a packet of unfiltered Gitanes. People who, in certain cases, easily passed the 70 or 80 year mark (or even more) even though their way of life should have sent them to the cemetery prematurely.

There is indeed another factor that weighs in the balance: our DNA, which (we believed) accounted for 20 to 25% of the differences in longevity between individuals. An often misunderstood statistic: it does not mean that your destiny is 25% sealed, but that the majority of the differences in lifespan between you and your neighbor come from your habits. It turns out that this calculation was flawed; a study published in the journal Science January 29, 2026 has just demonstrated that the influence of your genetic heritage would account for more than 55%.

Modern comfort: a confounding factor

Why such a gap? The researchers explain that old estimates mixed cabbage and carrots. A century ago, we died mainly from so-called causes extrinsic : illnesses, wars, work accidents or unsanitary conditions. In this context, having genetic variants protective against diseases inherent to old age (such as Alzheimer’s or heart disease) offered no statistical advantage if you were killed by tuberculosis before you could even age.

Today, thanks to vaccines and advances in medicine, we have ruled out these externalities and pure biological aging has become the dominant factor in our mortality.

To obtain a reliable measurement and this figure of 55%, the researchers behind this study used one of the key methods in behavioral genetics: the comparison of twins. By analyzing thousands of pairs of Scandinavian twins: true (called monozygotes) sharing 100% of their DNA and faux (dizygotes) sharing only half, the team was able to statistically isolate the heritability part.

Then, to refine this result, they crossed these data with twins separated at birth and siblings of American centenarians, while applying a filter: the exclusion of accidental deaths. By keeping only those that died naturally, they eliminated variables that masked the true influence of the genome. Without the influence of these external factors, genetic correlation has exploded to reach 55%.

Don’t go throwing away your gym membership and dropping bottles of wine while smoking like a fireman. This study in no way claims that your genetics condemns you at all costswhich would be profoundly deterministic and scientifically invalid. On the other hand, it demonstrates that once external risks are neutralized, the weight of heredity is mathematically more restrictive. Even with this increased heritability score, you still have a good half who will dictate your future : your access to care, your setting and your life choices, and, let’s be honest, a good big dose of chance. Isn’t it a little reassuring to know that, in any case, half the job is already done (or failed, depending on the hand your ancestors left you)?