If anyone has ever said you and your best friend are like “two peas in a pod,” they were definitely on to something. It turns out that we have a lot more in common with our friends than just our hobbies and outlook on life: we also share similar genetic code. In a genome-wide analysis, scientists from University of California-San Diego and Yale found that we are far more genetically similar to our friends than we are to strangers of the same population. In fact, researchers say our friends are as “related” — genetically speaking — as fourth cousins. Their findings suggest that, in addition to our physical and biological environment, our social networks also play an important role in human evolution.
Wearing the Same Genes
To draw the genetic link between friends, researchers focused on 1,932 subjects who participated in the 1948 Framingham Heart Study. The Framingham study has produced one of the largest datasets of both genetic information and details of social relationships. The researchers analyzed nearly 1.5 million markers of gene variations and compared pairs of unrelated friends against pairs of unrelated strangers. They found that, on average, we share about 1 percent of our genes with friends, which is a large number for geneticists. Friends shared enough genes to allow researchers to develop a “friendship score,” which predicted who would be friends with the same level of confidence as genetic tests for predicting obesity or schizophrenia. Researchers published their findings Monday in the Proceedings of the National Academy of Sciences.
Further, the findings, scientists say, weren’t a result of people tending to gravitate toward others with the same ethnic background. A vast majority of people in the Farmingham study had European origins, which ensured both friends and strangers were drawn from the same population.
How Friendship Smells
When researchers dug deeper into the data, they found that friends were most similar in genes controlling the sense of smell. Our sense of smell, researchers say, may draw us to certain environments, like a coffee house, where we meet people whose noses are tuned like ours. They added that our sense of smell could be one of the mechanisms we use to identify genetically similar friends. However, to be clear, more research is needed to explain how we find our genetically similar friends. In addition to similar genes, there were also certain places where friends tended to diverge genetically. Genes that controlled immunity to certain diseases were quite different between friends. That variance reduces the spread of disease, which researchers speculate could be an evolutionary advantage for befriending those with different immunities.
Interestingly, the genes that friends have in common seem to be evolving faster than other genes, according to the study. Thus, researchers conclude that our social environment could be a key evolutionary force, and may explain why human evolution has accelerated over the past 30,000 years. Although we don’t know how we choose our genetically similar friends, this study sure makes the expression “brother from another mother” all the more literal.
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