Massive Family Tree Sheds Light on War, Culture, Longevity

Online genealogies are helping researchers analyze population-level genetic trends. | MyHeritage

Taking advantage of an online public database shared by genealogy enthusiasts, researchers have created a massive, crowd-sourced family tree. It tracks the births, marriages and deaths of millions of people, shedding light on the impacts of war, culture and disease over the last several centuries. The results are featured in a study in the March 2 issue of Science.

Many people enjoy constructing their own family trees, digging deep into their roots to understand their ancestors. But looking at the connectivity between people can also be helpful for researchers examining genetic and cultural patterns.

In 2010, Yaniv Erlich was leading a group of researchers at Whitehead Institute when he read about using pedigrees, essentially family trees, as a means to study genetics. He was already passionate about using family trees, having submitted his own data to one of the largest online public genealogy databases, "Being a Geni user for some time, I thought that Geni can be a wonderful alternative to traditional methods for collecting family trees that do not scale well," explained Erlich, who now works as the chief science officer of MyHeritage (the Geni parent company) and is an associate professor at Columbia University.

With permission, he and his colleagues analyzed 86 million publicly available profiles from the website, which mostly reflect the histories of people in Europe and North America. They cross-referenced the family tree they created with publicly available death records from Vermont to confirm that the tree accurately reflects participants' histories.

The family tree they assembled shows the darker moments in recent human history; for example the massive waves of death during the American Civil War, World War I and World War II. But the tree also shows a reduction in child mortality during the 20th century, likely reflective of medical advances.

One of the analyses that Erlich and his team performed using the data focuses on the heritability of longer lifespans. Previous studies looking at families and genetics have estimated that the heritability of longevity is roughly 25%. By analyzing the data, Erlich found that heritability of longevity is substantially lower, at 16%.

"At 16%, longevity is one of the least heritable traits with medical relevance. As such, the genome holds much less influence about longevity than expected and our results help to explain why [genome studies] of longevity have failed to find a reliable signal so far," noted Erlich. "To some extent, it even questions the value of genome studies to understand human longevity — at best we could hope maybe to explain one-eighth of the variability in the population."

The researchers also used the genealogy data to explore migration patterns. They found that women migrate more than men in Western societies, but over shorter distances. As well, couples born between 1800 and 1850 showed a two-fold increase in their so-called marital distances, the distance between a married couple's places of birth. In 1800 the average marital distance was eight kilometers, but by 1850 it was 19 kilometers.

Intriguingly, the increase in marital distance occurred at the same time as an increase in genetic relatedness between couples (meaning individuals continued to marry relatives), contrary to the theory that people become more genetically diverse as they disperse.

The means of transportation also flourished at this time, offering people a chance to travel farther distances and increasing their ability to meet new people. Since people were still marrying people closer within their genetic circle at this time, Erlich and his team propose that cultural factors rather than mobility factors were behind this phenomenon.

MyHeritage has collected over 1.2 million kits in 13 months of operation, said Erlich, who noted that "we also have phenotypic surveys with the same questions as the UK Biobank," an international repository of health data from more than 500,000 participants. The surveys include questions regarding heritable aspects like eye color, widow's peak hairlines and even whether an individual has the ability to roll his or her tongue.

"We plan to harmonize these data with our genealogical maps. The idea is to keep publishing papers and making scientific discoveries at large scale like the paper. But we are just at the beginning of this journey," Erlich said.