Money & society · 2014
Are friends more genetically similar than strangers?
Yes, on average, in this observational study of human friendships. Across the genome, friends were more genetically similar than strangers, with the extra similarity comparable to that of distant relatives called fourth cousins. Some genetic variants showed the opposite pattern, however, and the study does not establish that genetic similarity causes friendship.
Details
Researchers compared small DNA differences across the genome between friends and between strangers. The overall increase in similarity among friends was comparable to the similarity of fourth cousins. This is a benchmark for the genetic difference, not a finding that the friends were actually related in that way.
The pattern was not uniform. A set of genes related to smell showed greater similarity among friends, while a set related to the immune system showed greater differences. The idea that these systems help form or maintain friendships remains a hypothesis.
A score based on genetic patterns also predicted friendship ties in a sample held back from the score’s development. The abstract does not report how accurate those predictions were.
Genetic variants that were more similar among friends also showed stronger evidence of positive selection—the process by which variants favoring survival or reproduction become more common over generations. The authors suggested that shared variants might provide an advantage through people's interactions and might have contributed to recent human evolution. That is an evolutionary interpretation, not a demonstrated benefit or causal explanation of friendship.
The abstract does not give the sample size or demographic details, limiting assessment of how broadly the findings apply.
What do you think?
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