How much of your future life is decided before you are born? A new analysis of more than a hundred records of twins suggests that genetics could halve people’s lifespans once death from accidents, infections and violence are removed.
The work, carried out at the Weizmann Institute of Science in Israel and published in the journal Science in January 2026, nearly doubling earlier estimates of the genetic component of longevity.
Some media have covered this issue in a harsh way, saying that almost 50 percent of a person’s life time is spent in the womb.
The researchers themselves describe a clearer picture in which genes and everything contribute to about half of the difference in how long people live, and there is still a large dose of contingency. So is your life set in stone or is there still room to move the needle?
What the researchers actually measured
The study, led by medical student Ben Shenhar, looked at large twin studies from Sweden and Denmark that followed identical fraternal twins. Because identical twins share almost all of their DNA while fraternal twins share about half, comparing their life spans can reveal how much more important genes are than environment.
These types of twin studies have been a classic tool in genetics for decades.
The team worked under the guidance of systems biologist Uri Alon at the Weizmann Institute and used mathematical models to reexamine the old records. They also used new datasets that, for the first time in this context, included raised twins, helping to isolate genes based on how families and neighborhoods shape health.
To sharpen the picture, the researchers even simulated the twins in a computer to test how different disease processes might affect the visible part of the gene.
Why is immigration so important?
Classic twin studies treated all deaths the same, regardless of whether someone died peacefully in their 90s or of cholera in their thirties. The new work focuses on extrinsic disease, an umbrella term for disease that comes from outside the body, including infectious diseases, accidents and violence.
In the era before antibiotics and modern sanitation, these external risks were ten times more common than today, especially in the Scandinavian groups that the team examined.
That’s important because when the cause of death isn’t in the histopathology, early death can mask the fact that twins share a strong biology of longevity.
If one twin lives to 90 due to natural aging and the other dies at age 30 due to an epidemic, a simple analogy would say that genetics doesn’t matter much. By building a predictive model and filtering out the disease from abroad, the researchers showed that previous work had systematically underestimated the contribution of genetics to health.
Half genetics, half everything
Once those external causes are accounted for, Weizmann’s team concludes that human life, the part driven by aging processes and inherited risk, is almost 50 percent.
For many years, it was thought that human lifespan was shaped almost entirely by non-genetic factors, “raising doubts about the genetics of longevity,” Shenhar said in a Weizmann news release.
That number is similar to the inheritance of many other complex traits and is consistent with studies of the lives of mice and other animals.
Early work on twins suggested that only 20 to 25 percent of life span was genetic, and other large family studies put the number closer to 6 percent.
A 2019 meta-analysis of genome-wide association studies in Nature Communications showed several genetic variants associated with longevity, but their effects looked mild against those lower genetic estimates. With the new numbers, the researchers say there is a strong incentive to continue the hunt for protective genetic variants that slow aging or delay disease.
What could this mean in your life?
For people reading this study between work emails and dinner plans, the obvious question is what it means for everyday choices.
The genetic contribution of about 50 percent does not cancel out the influence of diet, smoking, exercise, pollution or access to health care, which still make up the other half of the picture. Researchers and doctors emphasize that the way you live can ease or increase the risks written in your DNA.
The new work is also consistent with genetic studies that appear to protect some people into old age, such as those highlighted in Nature Communication a meta-analysis of genome wide association studies that showed variants at the APOE locus and other pathways.
Lead author Ben Shenhar has identified up to 100 people without major deaths as examples of people who can take groups of such protective measures, although most of us won’t be so lucky. It’s a fascinating idea that part of your life time may have been created before you were born, though it’s far from fixed.
Visual text on Science argues that the new estimates should prompt scientists to rethink long-held ideas about the biology of aging and invest more in genetic studies of longevity.
At the same time, Weizmann’s group realizes that their data comes mainly from Scandinavian and European populations, so future work will need to assess how well the results hold up in other groups and the current message is that although genes are very important, lifestyle and environment still control the whole story.
A large study was published in the journal Science.
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