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Study finds people select genetically similar friends

Friendships in adulthood.
Friendships in adulthood.
JLS Media CC BY-SA 2.0

Multiple factors are in play in human’s selection of other people as friends but genetics has been found to be a basis for friendship on multiple levels. Nicholas A. Christakis from Yale University and James H. Fowler at the University of California at San Diego are the first to present confirmed proof of a genetic component in people’s selection of their friends. The findings were reported in the July 14, 2014, edition of the journal Proceedings of the National Academy of Sciences.

The findings are based on an examination of the genetic structure of 1,932 people that were not related to each other nor involved in a sexual or spousal relationship of any kind. The researchers used data from the Framingham Heart Study. The Framingham Heart Study is the largest set of genetic data available that involves enough people to provide an analysis of friendship relationships in the group.

The criteria in the study were simply that a person had a friendship relationship with another individual in the study group. The researchers found that friends share about one percent of their genes. The development of friendship was not found to have a racial basis. The level of genetic relationship is on a par with the genetic information used to diagnose many diseases.

Selecting friends that have a similar genetic structure has several evolutionary advantages according to the researchers. The genes that were most involved in the selection of friends were associated with smell. Genes that confer immunity from disease had the least impact on the selection of friends. People who like the smell of the same things and the smell of each other were more likely to be friends. Having friends that are immune to different diseases confers a protective advantage by association and transfer of the immunity to disease between people.

The researchers postulate that their study indicates that the genes that cause people to select other people as friends have evolved more rapidly than other genes in the last 30,000 years of human existence. Human health has become dependent on association with friends that have immunity to diseases that a given individual does not. Friendship is a multifaceted behavior but genetics plays a substantial role in the selection of friends. The study confirms the idea that friends are the family you choose.