Because of a number of confounding variables, getting an accurate measure of the heritability of the human lifespan is challenging. (For comparison, measurements of lifespan heritability in laboratory mice are much higher, around 38 to 50 percent.) Research published today in Science shows that heritability in the human lifespan is double past estimates—up to 55 percent. The deceptively simple equation for heritability is the additive genetic variation of a given trait divided by the phenotypic variation of the trait. That means that as phenotypic variation increases, heritability goes down.