Our lifespans may be half down to genes and half to the environment

For people living in these nations, it may be no surprise that their lifespans are probably half down to their genes and half to their environment. But earlier studies of the twin data, performed decades ago, concluded that genes explained only a quarter of the variation in human lifespans. If seeds are planted in a flat, uniform field, almost all variations in height will be down to genetics. Sign up to newsletterFor estimating heritability in human traits, geneticists often compare twins raised in the same household with those raised separately. “It remains a major puzzle why so few human longevity-associated genes have been identified,” says de Magalhães.