For decades, the explanation for why some people live longer than others has focused on the environment: lifestyle, diet, diseases, or chance. However, new research published in Science challenges this approach and assigns genetics a much more decisive role than previously thought. The study, led by biologist Uri Alon , argues that up to 55% of the variation in human lifespan is determined by genetic inheritance.

The key to the study lies in differentiating between extrinsic causes of death—such as accidents, infections, or violence—and intrinsic causes, directly linked to biological aging. According to the authors, the high external mortality rate in the 19th and 20th centuries masked the true role of genetics in longevity for many years. By statistically removing these external deaths, the heritability of lifespan increases significantly, doubling previous estimates.

To reach these conclusions, the team reanalyzed large databases of identical and fraternal twins from Denmark and Sweden, as well as siblings of centenarians in the United States. In total, nearly 16,000 pairs of related individuals were studied . Mathematical models show that, as external mortality decreases—today ten times lower than at the end of the 19th century—the influence of genetics becomes much more evident.

The finding does not diminish the importance of lifestyle, but it does qualify its scope. Approximately half of longevity would still depend on modifiable factors, such as diet and exercise, while the other half would be determined by heredity. Independent experts believe the study could shift the current paradigm and strengthen the search for key genetic variants in aging , with direct implications for biomedical research and the prevention of age-related diseases.