World's Biggest Family Tree Contains 13 Million People—and It Shows When Cousins Stopped Having Sex

Researchers have created what is the world's largest family tree containing the records of around 13 million people. The dataset, which was put together using interconnected online genealogy profiles, has revealed fascinating insights into the past 500 years of North American and European history.

To create the family tree, Yaniv Erlich—a computer scientist at Columbia University and lead author of the study—and colleagues downloaded 86 million public profiles from, one of the largest collaborative genealogy websites.

They then used mathematical analysis to organize the data, resulting in a vast interconnected family tree that spans 11 generations on average, documenting births, deaths and marriages. In theory, if the data extended back another 65 generations, the tree would converge on a single common ancestor, the researchers said. Their work is published in the journal Science.

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

"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," Erlich said in a statement. "We hope that this dataset can be useful to scientists researching a range of other topics."

In the above 6,000 person family tree, individuals spanning seven generations are represented in green, with their marital links in red. Columbia University

Around 85 percent of the people included in the data originate from either Europe or North America, giving researchers an unprecedented glimpse into the interconnected history of the two regions.

Among many intriguing insights, the family tree shines a light on shifting patterns of marriage and migration over time. For example, before 1750, most Americans found a spouse within six miles of their birthplace. However, after 1950 this distance had increased to around 60 miles, the researchers said.

In addition, before 1850, marrying a relatively close family member was common—on average people wedded their fourth cousin. Previously, it was thought that people in the West stopped marrying their close relatives due to the impact of improved transport networks, which caused people to be born further away from their extended families.

However, the data showed that for a 50-year period between 1800 and 1850, people traveled farther than ever before to find a spouse—around 12 miles on average—yet were more likely to marry a fourth cousin.

In light of this, the researchers suggest that people stopped marrying their fourth cousins not due to increased mobility between different regions, but because the practice became less socially acceptable.

On the topic of migration, the family tree also showed that women in Europe and North America have migrated more than men in the last 300 years, although, when men did migrate, they tended to travel much larger distances on average.

"The reconstructed pedigrees show that we are all related to each other," Peter Visscher, a quantitative geneticist at the University of Queensland who was not involved in the study, said in a statement. "This fact is known from basic population history principles, but what the authors have achieved is still very impressive."

The new research also has implications for our understanding of human longevity. Scientists think that our life spans are in some way determined by our DNA; however, identifying the genes responsible and their degree of influence has been difficult.

But the new family tree enabled the researchers to compare distantly related family members, leading them to conclude that 16 percent of our lifespan—roughly equating to an average of five years—is determined by inherited genes, a lower figure than what was expected.