Now scientists think they may have unlocked a key secret to long life – quite simply, genetics. Such “extrinsic mortality” increases with age, as people often become more frail. Prof Uri Alon and colleagues at the Weizmann Institute of Science in Israel say the true genetic contribution to the variation in human lifespan has been masked. They removed the impact of extrinsic mortality to reveal the signal from biological ageing, which is caused by genetics. The other 50% of variation in human lifespan, they said, was probably explained by factors such as random biological effects and environmental influences.