Long life spans tend to run in families, its believed to be attributed through genes. But now, a large new study of data from the genealogy website Ancestry reveals that genetics may play less of a role in life span than previously thought. Previous studies failed to take into account a pattern of human relationships: that people tend select romantic partners with similar traits to their own. The findings mean that previous studies may have overestimated the heritability of life span, the researchers said.researchers analyzed information from more than 400 million people using publicly available family trees from Ancestry. Because the researchers needed to know the life span of these individuals, the study looked at only those who were born in the 1800s or early 1900s and were deceased. With the data they found that it doesn't have to do with family history or similar living environments, they looked at assortative mating. The large data set allowed researchers to examine the effect of what's called assortative mating, the phenomenon in which people tend to select spouses who are similar to themselves. If assortative mating was what they did, it would mean that factors that are important for life span tend to be similar among spouses. So, spouses tend to have the same life span because they picked a spouse that was like them.