Last updated October 1, 2020 at 10:41 am
Using crowdsourced data from a genealogy website, scientists have linked 13 million people through history.
Your Christmas lunch is about to get a whole lot more crowded. Scientists have created the largest “family tree,” made up of 13 million people linked through time.
What it reveals is amazing, tracking over 500 years of marriage and migration in Europe and North America to expose the impact of human culture and the spread of genes around the world.
The history of humanity
The study revealed some massive societal changes which were reflected in the changing genetic profiles of populations.
These included changing attitudes towards marriage, migration, historical events such as elevated death rates at military age during the American Civil War, and both world wars, and a reduction in child mortality during the 20th century.
By looking at the birth years and locations of the profiles around the world, the researchers found they could watch the migration of humans out of Europe, including to North America, South Africa and Australia, as well as the migration by settlers across America.
Before 1750, most Americans married someone from within 10 kilometres of where they were born. Fast forward 200 years, and for those born in 1950, that distance had stretched to about 100 kilometres.
Before 1850, marrying in the family was common. On average, they would marry a fourth cousin, compared to seventh cousins today.
Curiously, the researchers found that between 1800 and 1850, people travelled further to find a mate (19 kilometres), but were more likely to end up marring a fourth cousin or closer than in previous years.
The researchers suggest that this 50-year delay between the increase in mobility and change in marriage choice could well mean that it was a change in social norms, rather than increased mobility, that may have led people to move away from marrying relations.
The tree also shows that over the past 300 years, women were more likely to have migrated from area to area than men, however when men did move, they travelled significantly further on average. Matching this pattern, they found that fathers were more likely than mothers to have been born in a different country than their offspring.
The genetics of long life
The researchers also used their compiled data to see if they could unpick the influence of genetics on long life, versus the effects of lifestyle choices – so called nature vs nurture.
They used data from 3 million relatives born between 1600 and 1910 who had lived past the age of 30, and removed anyone who had died in wars or natural disasters.
By comparing how long someone lived compared to their relatives, they found that someone’s genes explained about 16 percent of differences in longevity.
In other words, having good genes could extend someone’s life by an average of five years. “That’s not a lot,” said Yaniv Erlich from Columbia University, who headed the research. “Previous studies have shown that smoking takes 10 years off of your life. That means some life choices could matter a lot more than genetics.”
The study also showed that the genes that influence longevity act independently rather than interacting with each other, a phenomenon called epistasis.
If some genetic variants act together to influence longevity, the researchers would have seen a greater similarity between closely related individuals who share more DNA, and thus more genetic interactions.
However, they found a linear link between longevity and genetic relatedness, ruling out widespread epistasis.
Building the tree
The crowdsourced project used data from 86 million public profiles on the genealogy website Geni.com, owned by a company for which Erlich acts as Chief Scientific Officer.
Analysis using mathematical graph theory constructed several small family trees, as well as the giant single tree made up of 13 million people spanning an average of 11 generations.
To find a single ancestor for that entire tree, they would theoretically need to go back another 65 generations.
“The reconstructed pedigrees show that we are all related to each other,” said Peter Visscher, a quantitative geneticist at University of Queensland who was not involved in the study. “This fact is known from basic population history principles, but what the authors have achieved is still very impressive.”
The researchers have made the data and tree available for other scientists to study through the website FamiLinx.org
The research has been published in Science.
Video courtesy of MyHeritage and Columbia University