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The World’s Largest Family Tree Shows When People Stopped Marrying Their Cousins

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Researchers put together the world’s biggest family tree that has records on around 13 million people. They used interconnected online genealogy profiles to create the dataset, which has revealed some interesting things about the past 500 years in European and North American ancestry.

Yaniv Erlich, a computer scientist at Columbia University and lead author of the study, and a team of scientists downloaded 86 million public profiles from – one of the world’s largest online genealogies, Newsweek reports.

The team then used mathematical analysis to examine and organize the information, building an interconnected family tree that spans around 11 generations. The tree covers births, deaths and marriages. Theoretically, if the tree were to go back another 65 generations, it would all come down to one common ancestor.

The study states, “Family trees have vast applications in multiple fields from genetics to anthropology and economics. However, the collection of extended family trees is tedious and usually relies on resources with limited geographical scope and complex data usage restrictions.”

Erlich said,

Through the hard work of many genealogists curious about their family history, we crowdsourced an enormous family tree and boom, came up with something unique.

He added, “We hope that this dataset can be useful to scientists researching a range of other topics.”

About 85% of the people included in the family tree came from either Europe or North America, providing some insights into the shifting patterns of migration and marriage. Before 1750, for example, most Americans found someone to marry within six miles from where they were born. But after 1950, the distance widened to 60 miles.

In addition, before 1850, people married close family members as a common practice. Between 1800 and 1850, people traveled even farther to find a spouse, but were still more likely to marry a fourth cousin.

The researchers suggest that this means people stopped marrying cousins not because of accessibility to transportation, but because the practice became less socially acceptable.

The study was published in Science.

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