Although genetic factors are known to influence the human aging process, the proportion of life span and longevity variation explained by them is still controversial. We evaluated the genetic contribution to life span using historical data from three Alpine communities in South Tyrol, Italy. We estimated the heritability of life span and survival to old age (longevity), and we assessed the hypothesis of a common genetic background between life span and reproduction. The heritability of life span was 0.15 (SE = 0.02), whereas the heritability of longevity increased from 0.20 to 0.35 as the longevity threshold increased. Heritability estimates were little influenced by shared environment, most likely due to the homogeneity of lifestyle and environmental factors in our study population. Life span showed both positive association and genetic correlation with reproductive history factors. Our study demonstrates a general low inheritance of human life span, but which increases substantially when considering long-living individuals, and a common genetic background of life span and reproduction, in agreement with evolutionary theories of aging.