Taking advantage of an online database of public data shared by genealogy enthusiasts, researchers have created a massive, crowd-sourced "family tree." By tracing the lives of millions of people, their tree brings to light additional impacts of human culture on the spread of genetic information, suggesting, for example, that a recent reduction in genetic relatedness in Western societies had more to do with shifting cultural factors than it did with the advent of transportation. To date, constructing population-scale family trees has been a labor-intensive process. Here, by leveraging available social media data, Joanna Kaplanis, Yaniv Erlich, and colleagues created such a tree; they analyzed records from 86 million publicly available profiles from Geni.com, a crowd-sourced genealogy website. The Geni.com data reflects historical events and trends such as elevated death rates at military age during the American Civil War, WWI, and WWII, and a reduction in child mortality during the 20th century. By comparing the data from Geni.com to traditional genetic studies exploring heritability, the authors found a similar, albeit smaller, estimate of the heritability of longevity. Looking at migration patterns, they uncovered that females migrate more than males in Western societies, but over shorter distances. As well, couples born between 1800 and 1850 showed a two-fold increase in their so-called marital distances, the authors say, from 8 kilometers in 1800 to 19 kilometers in 1850; intriguingly, the increase in marital distance occurred at the same time as an increase in genetic relatedness (individuals continued to marry relatives), contrary to the theory that people become more genetically diverse as they disperse. Kaplanis et al. write, "From these results, we hypothesize that changes in 19th century transportation were not the primary cause for decreased consanguinity. Rather, our results suggest that shifting cultural factors played a more important role in the recent reduction of genetic relatedness of couples in Western societies."
Notably, to provide additional samples, alleviating concerns that Geni.com users do not reflect the average person sampled, the researchers obtained every death certificate issued in the state of Vermont, which has an open policy about death certificates, from 1985 to 2000, for a total of nearly 80,000 records. After locating the death certificates of nearly 1,000 Geni.com profiles for individuals who died in Vermont during the same period, the researchers compared key socio-economic attributes between Geni.com users and the rest of the Vermont database. Importantly, each attribute showed nearly perfect concordance, say the authors, between the Geni.com profiles and the rest of the database.