A lot of our ancestors married their close relatives Alan Collins / Alamy Stock Photo

Think you’ve got a big family? Check out the world’s biggest family tree, containing 13 million people. The giant family tree is the largest of several built using crowd-sourced data, each of which tells a tale about the history of Western civilisation.

Joanna Kaplanis at the Wellcome Trust Sanger Institute in Cambridge, UK, and her colleagues, collected 86 million publicly-available profiles from Geni.com. Users on this crowd-sourcing website create family trees, which are then merged with others when matches occur.

After cleaning up the data, the team was able to dispel a long-standing myth.


It was thought that people in the west stopped marrying their close relatives in the 19th century, because improved transport meant that people were born further away from their families. But the family tree proved otherwise.

“Even though people started to be born further away from their families during the early 19th century, they were still marrying cousins for 50 years,” says Kaplanis. It seems the eventual decrease in inbreeding was more to do with cultural influences. “It just became less socially acceptable.”

Long life

The new family tree is also shedding light on longevity.

Read more: Inbreeding shaped the course of human evolution

We know siblings tend to live to a similar age, as do parents and their children. This suggests that lifespan is at least somewhat heritable, but we haven’t found many of the genes responsible. “When you’re looking at close relatives like siblings and parents, there’s a lot of shared environment, so it’s difficult to tease apart the genetic influence,” says Kaplanis.

The gigantic family tree allowed the team to compare the lifespans of family members who were more distantly related and living in different towns. The analysis suggests that around 16 per cent of the variance in our lifespan can be explained by inherited genes.

That “is on the lower end of what previous research had suggested,” says Kaplanis.

Journal reference: Science, DOI: 10.1126/science.aam9309