Using crowdsourced data from a social genealogy site, a team of geneticists put together a family tree that includes 13 million people. Researchers used this behemoth of a family tree to investigate how much heredity influences longevity and to track shifts in migration habits and marriage taboos in Europe and North America over the last 300 years.

Tree building

Putting together an extended family tree on such a large scale is normally a daunting and tedious task for researchers. They typically have to ferret out records from churches and county courthouses, and most of the time those records are the old-fashioned paper kind. Tracing long-distance connections using these records can be a nightmare.

But the payoff is big, because tracking that many people’s relationships can yield insights into cultural trends, economics, genetics, and population movements. That’s especially true if researchers can combine the family tree with genetic or health data for the people listed.