Daijiworld Media Network - London

London, Feb 3: How much our genes determine how long we live has long intrigued scientists, with conventional wisdom suggesting genetics account for about 20–25 per cent of human lifespan, while lifestyle and environment do the rest. However, a new study published in Science challenges this view, indicating that the genetic contribution could be significantly higher under modern conditions.

Researchers argue that earlier estimates did not fully consider how causes of death have changed over time. In the past, many deaths were due to external factors such as infections, accidents and poor living conditions. Today, particularly in developed countries, most people die from age-related diseases like heart ailments and dementia, which are more closely linked to biological ageing.

To arrive at clearer estimates, scientists analysed extensive data from Scandinavian twins, excluding deaths from external causes, and also examined twins raised apart along with siblings of centenarians in the United States. When deaths from accidents and infections were removed from the analysis, the estimated genetic influence on lifespan rose sharply to about 50–55 per cent.

The researchers caution, however, that this does not mean genes have suddenly become more powerful. Rather, improvements in healthcare, nutrition, vaccination and living standards have reduced environmental risks, making genetic differences appear more prominent. The study highlights that heritability is not fixed but varies depending on social and historical conditions.

Even with the higher estimate, the authors note that nearly half of lifespan variation is still shaped by environment, lifestyle, healthcare access and random biological processes. They emphasise that longevity results from a complex interaction between genes and environment, and that there is no single formula for a long life.

The findings underscore the need to better understand genetic mechanisms of ageing while reinforcing that healthy living continues to play a crucial role in determining how long and how well people live.