The findings challenge the prevalent view that life span is determined mostly by lifestyle and environmental factors. Determining how much of human life span results from genes is important for understanding aging more generally. This is caused by a dip in extrinsic mortality during those years. The findings represent a pivot in our understanding of life span, Shenhar says. “We’re bringing back life span — which was thought to be very different — into the same playing field with the rest of the traits.”This new calculation of life span heritability also more closely resembles what scientists have estimated in laboratory animals such as mice and flies.