Quantitative analysis of millions of relatives Human relationships, as documented by family trees, can elucidate the heritability of a host of medical and biological parameters. Kaplanis et al. collected 86 million publicly available profiles from a crowd-sourced genealogy website and used them to examine the genetic architecture of human longevity and migration patterns (see the Perspective by Lussier and Keinan). Various models of inheritance suggested that life span is predominantly attributable to additive genetic effects, with a smaller component from dominant genetic inheritance. The data also suggested that relatedness between individuals is less attributable to advances in human transportation than to cultural changes. Science , this issue p. 171 ; see also p. 153