Human lifespan is probably more influenced by lifestyle and other environmental factors than by genetics. Studies of insects and rodents have shown that genetic mutations can modify lifespan. But studies of identical twins suggest that heredity accounts for 35% or less of differences in lifespans.

Findings from at least six different research groups on the genetics of aging have shown a far smaller contribution of heredity to long lifespan than had been anticipated. Studies of identical twins -- twins who share the same genetic makeup -- are in good agreement that whether reared together or reared apart as children, there is little correlation in lifespan once the twins reach middle age.

Science (1997;278:407-411)