This study investigated the historical trend in resemblance between first-degree relatives for age at death. Data from genealogies of six New England families (N = 13,656) were divided into nine 25 year birth cohorts, 1650-1874, to test the hypothesis that familial influence on human longevity has changed during the past 300 years. Heritability (h2 ) for longevity demonstrated no historical trend, whether calculated by regression of offspring's longevity on paternal, maternal, or mid-parental longevity or by intraclass correlations (t) among sibships. Ninety-five percent confidence intervals (C.I.) for h2 (additive genetic variance) were in the range 0.10-0.33 for parent-offspring regressions and 0.16-0.22 based on mean of sibship regressed on mean of parents. Based on sibship t, the 95% C.I. for the upper limit to h2 (which includes variance contributions caused by dominance interactions and common developmental environment as well as additive genetic effects) was 0.33-0.41. In this socially elite sample, the statistical contribution of first-degree relatives to age at death has varied within a historically consistent range over the past 300 years, directly implying a persistent genetic influence on longevity. The magnitude of this influence with respect to additive genetic variance, about 10-30%, may overestimate h2 because of the elite nature of the sample. Nevertheless, these results support a genetic component to lifespan even though the majority of variation in human longevity is not explained by genetic factors.
Copyright © 1991 Wiley-Liss, Inc., A Wiley Company.