Friendship and natural selection

It turns out that your friends can be genetically so similar to you that they are about the same as fourth cousins. I hate to think of the awful cross breeding that has created both my friends and myself.
From: Proceedings of the National Academy of Sciences.


More than any other species, humans form social ties to individuals who are neither kin nor mates, and these ties tend to be with similar people. Here, we show that this similarity extends to genotypes. Across the whole genome, friends' genotypes at the single nucleotide polymorphism level tend to be positively correlated (homophilic). In fact, the increase in similarity relative to strangers is at the level of fourth cousins.

Source: Friendship and natural selection