Subscribe to The Post Most newsletter for the most important and interesting stories from The Washington Post. Uri Alon was long puzzled by a textbook statistic: Longevity, the thinking went, was about 20 percent in our genes.“That makes you think what’s the rest of the 80 percent: Is it the lifestyle? Why should we study genes for lifespan if it’s not that important? It kind of bothered me,” said Alon, a physicist turned systems biologist at the Weizmann Institute of Science in Israel.AdvertisementAdvertisementAlon uses mathematical models to understand complicated biological problems, and he and his colleagues built one to reexamine the factors that define the contours of human lifespan in a Science study published earlier this year.The original studies that were used to estimate how much of lifespan was inherited were studies of Scandinavian twins from the tail end of the 19th century.During that era, “extrinsic” mortality – deaths that aren’t related to the deterioration of aging, such as accidents, violence or deaths from infections that are now uncommon because of better nutrition, therapies and hygiene – was high.His team examined a database of Swedish twins born later, between 1900 and 1935, and found that these extrinsic deaths were masking the inherited component of lifespan. When they applied their model, designed to remove extrinsic deaths, to databases of Scandinavian twins and the siblings of people who lived to at least 100, the heritability of lifespan markedly increased – to about half.AdvertisementAdvertisementIt isn’t that the old studies were wrong: They were focused on longevity in a different era, a generation born between 1870 and 1900. “At that time, people died of pneumonia and tuberculosis, and not a lot of people made it to their 40s,” Alon said. “In that situation, who cares how long your parents lived? G …
