Every morning, another headline tells you to eat kale, run five miles, or quit drinking to live longer. Lifestyle advice dominates the longevity conversation. But a paper published this week in *Science* from the Weizmann Institute of Science flips that script. Researchers Ben Shenhar and Uri Alon have found that genetics accounts for roughly half of the variation in human lifespan — more than double the previous consensus.
The team analyzed three twin databases from Sweden and Denmark
The study drew on tens of thousands of twin pairs across three registries. Crucially, the researchers included data from **twins raised apart** for the first time in such an analysis. Identical twins who grew up in different environments share the same genome but experience different lives, making it possible to separate genetic influence from environmental noise. Earlier studies lacked this data. The team built mathematical models and ran virtual twin simulations to isolate deaths caused by aging from those caused by accidents, infections, and other external factors (what scientists call "extrinsic mortality"). The result: genetic factors explain about **50%** of the differences in how long people live. Previous estimates ranged from 20-25%, and some large-scale studies put the number below 10%. The genetic influence was even stronger for specific causes. For deaths from dementia before age 80, genetics accounted for roughly **70%** of the risk — far higher than for cancer or heart disease.
Older studies lumped all deaths together and averaged them out
Past research analyzed overall mortality rates without breaking down causes of death. A car crash victim and a centenarian who died of old age were treated the same way in the statistical model. That approach drowns the genetic signal in environmental noise. This new study took a different path. The team filtered death records by cause and used mathematical modeling to isolate "aging deaths" from everything else. Once they did that, the genetic contribution became more than twice as visible. Shenhar put it plainly: "For a long time, it was thought that human lifespan is determined almost entirely by non-genetic factors. These results show that genetic influence is high, and they motivate research to find the gene variants that extend life."
The real shift developers and researchers will feel is a change in research direction
If genetics determines half of lifespan, the field of longevity research pivots. Scientists will focus more on hunting down specific genes. Finding a longevity-associated gene variant could open the door to drugs or gene therapies that extend life. Conversely, the relative importance of environmental factors — diet, exercise, pollution — shrinks. The team says the same analytical method could be applied to other complex human traits, such as height or intelligence. The research was supported by the Sagol Institute for Longevity Research and the Knell Family Institute for Artificial Intelligence, among others.
This study doesn't tell you to stop exercising. It tells you that the search for the biological levers of aging has just gotten a much clearer target.
