Scientists have created the largest ever human family tree by using millions of interconnected online genealogy profiles offering fresh insights into the last 500 years of marriage and migration in Europe and North America as well as the role of genes in longevity.
The family tree involves a whopping 13 million people that has been created by sifting through the 86 million public profiles downloaded from Geni.com, one of the world’s largest collaborative genealogy websites, and used mathematical graph theory to clean and organize the data.
The family tree connects 13 million people spanning an average of 11 generations. The dataset details when and where each individual was born and died, and mirrors the demographics of Geni.com individuals, with 85 percent of profiles originating from Europe and North America.
The researchers verified that the dataset was representative of the general U.S. population’s education level by cross-checking a subset of Vermont Geni.com profiles against the state’s detailed death registry.
Marriage, Migration and Genetic Relatedness Industrialization profoundly altered work and family life, and these trends coincide with shifting marriage choices in the data. Before 1750, most Americans found a spouse within six miles (10 kilometers) of where they were born, but for those born in 1950, that distance had stretched to about 60 miles (100 kilometers), the researchers found.
Data indicates that before 1850, marrying in the family was common — to someone who was, on average, a fourth cousin, compared to seventh cousins today, the researchers found. Curiously, the researchers found that between 1800 and 1850, people traveled farther than ever to find a mate — nearly 12 miles (19 kilometers) on average –but were more likely to marry a fourth cousin or closer. Changing social norms, rather than rising mobility, may have led people to shun close kin as marriage partners, they hypothesize.
In a related observation, they found that women in Europe and North America have migrated more than men over the last 300 years, but when men did migrate, they traveled significantly farther on average.
Genes and Longevity To try and untangle the role of nature and nurture in longevity, the researchers built a model and trained it on a dataset of 3 million relatives born between 1600 and 1910 who had lived past the age of 30. They excluded twins, individuals who died in the U.S. Civil War, World War I and II, or in a natural disaster (inferred if relatives died within 10 days of each other).
They compared each individual’s lifespan to that of their relatives and their degree of separation and found that genes explained about 16 percent of the longevity variation seen in their data — on the low end of previous estimates which have ranged from about 15 percent to 30 percent.
The results indicate that good longevity genes can extend someone’s life by an average of five years. Significantly, the study also shows that the genes that influence longevity act independently rather than interacting with each other, a phenomenon called epistasis. Some scientists have used epistasis to explain why large-scale genomic studies have so far failed to find the genes that encode complex traits like intelligence or longevity.
If some genetic variants act together to influence longevity, the researchers would have seen a greater correlation among 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.