The expression “friends are the family you choose” may be a well worn cliché, but as scientists from the University of California and Yale have discovered, there may be more scientific truth to this statement than previously thought.
In fact, a genome-wide analysis of almost 2,000 people has revealed that we are just as likely to be related to our friends as we are to our fourth cousins, meaning friends share roughly one percent of their DNA with one another.
"One per cent may not sound like much to the layperson," says researcher Nicholas Christakis. "But to geneticists it is a significant number. And how remarkable: Most people don't even know who their fourth cousins are! Yet we are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin."
The discovery that reinforces the modern day belief that much of our social behavior, including group living and altruism, has it roots in the proliferation of shared DNA. Put simply, it makes sense to look out for those who may go on to reproduce and pass similar genes to your own into the next generation.
The study also revealed that friends are most similar in their olfactory genes, the genes we use to smell. One possible explanation for this could be that friends are drawn to similar environments. For example, individuals that like the smell of coffee may spend a lot of time in cafes, where they are likely to meet and befriend like-minded people.
It could also be the case that some gene-controlled traits can only function if they are shared amongst friends.
"The first mutant to speak needed someone else to speak to”, says Christakis. “The ability is useless if there's no one who shares it. These types of traits in people are a kind of social network effect."
Conversely, friends are least likely to share genes that control the immune system. This makes sense evolutionarily speaking because having different illness tolerances means disease is less likely to spread.
Another interesting discovery by the research was that genes shared by friends seem to be evolving faster than other genes, suggesting that our social relationships could be a driving force on human evolution.