World’s Largest Family Tree Reveals When The Americans Stopped Marrying Their Cousins

You may have heard of Americans and Europeans marrying into their family centuries ago. This was true, especially before the Industrial Revolution. During that time, people didn’t travel far to find potential spouses. But by the 19th century, things started to change and people eventually stopped marrying their cousins.

That time, with the rise of mass transportation and the shifts in social norms, families became more dispersed. Later on, spouses became less and less related. This is just one of the many insights that can be gathered in the world’s largest, scientifically-vetted family tree.

For the research, which was recently published in the journal Science, the researchers assembled 5 million family trees.

The authors compiled and analyzed 86 million public profiles from Geni.com, a genealogy-driven social media site. The largest tree they assembled consisted of 13 million people and spanned 11 generations. The researchers then used their data to test several hypotheses on genetics and history.

Yaniv Erlich, the chief science officer of MyHeritage, the parent company of Geni.com and senior author of the paper titled “Quantitative analysis of population-scale family trees with millions of relatives,” was quoted as saying:

“You can harness the hard work of so many people around the globe just documenting their own family history, and learn something about humanity.”

The study is one of the latest examples of researchers using crowdsourced data collected by private companies.

This trend in research is questioned by some experts as it raises issues about 1) just how representative the data collected are, and 2) how the private companies might have vested interests that can influence the research.

Emily Klancher Merchant, a science and technology studies professor at the University of California, Davis, was quoted as saying:

“When private companies control the data and fund the research, they’re the ones gatekeeping what kind of science gets done.”

In genealogy research, however, there aren’t many efficient ways to gather up-to-date data.

In the past, researchers have had to dig through countless church records and birth and death certificates to assemble large family trees. For this particular research, Dr. Erlich and his co-authors said they made sure to validate the crowdsourced data they gathered. As written in their discussion:

“In this work, we leveraged genealogy-driven media to build a dataset of human pedigrees of massive scale that covers nearly every country in the Western world. Multiple validation procedures indicated that it is possible to obtain a dataset that has similar quality to traditionally collected studies, but at much greater scale and lower cost.”

With the study’s limitations, the researchers were still able to reach some interesting conclusions, including the higher likelihood of mothers to migrate than fathers and a lower heritability of life span than others have reported.