Friends not biologically related, resemble each other genetically. Do you agree? –
Abstract
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. However, certain genotypes are also negatively correlated (heterophilic) in friends. And the degree of correlation in genotypes can be used to create a “friendship score” that predicts the existence of friendship ties in a hold-out sample. A focused gene-set analysis indicates that some of the overall correlation in genotypes can be explained by specific systems; for example, an olfactory gene set is homophilic and an immune system gene set is heterophilic, suggesting that these systems may play a role in the formation or maintenance of friendship ties. Friends may be a kind of “functional kin.” Finally, homophilic genotypes exhibit significantly higher measures of positive selection, suggesting that, on average, they may yield a synergistic fitness advantage that has been helping to drive recent human evolution.
Christakisa NA, Fowlerd JH: Friendship and natural selection, PNAS 2014; http://www.pnas.org/cgi/doi/10.1073/pnas.1400825111
Rather than being affecting the genotype of our friends, I would think of such results to be likely to uncover some genetic base underlying friendship-related characters that are simply not believed to be controlled by genes and genetic systems. It made me think of the answer of another question: How talents, such like painting, are inherited in the same family?
I think it also possible that developing friendships is, evolutionarily speaking, and extension of detecting family members. Reliable detection of family members is more or less necessary for kin selection and there are a number of ecological cues we use for this purpose, such as comparing phenotypic similarity etc. This means that we are designed to like and trust phenotypically similar individuals. And because phenotypes reflects genotypes, we then will also like individuals who are more genotypically similar to us than the base-line expectation.
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