Research suggests that similarity could be as much as 1%.
We share more genes with our friends than we do with strangers.
If they asked us what criteria we follow to choose our friends, surely almost all of us would answer that having similar likes and dislikes would be one of the reasons. But it seems that people united by a friendship have more in common than mere hobbies: genes. Or, at least that's the result of a study by researchers at Stanford and Wisconsin University.
Numerous sociological studies had pointed to the existence of a possible tendency that would make some people more attracted to establish bonds of friendship with others that had physical characteristics with a certain similarity (body size, weight, hair color...). The study authors wanted to see if there could be indications of a biological basis for such behavior, and collected genetic samples from more than 12,000 people.
The results of the experiment revealed that, indeed, in most cases there was a greater genetic similarity between people who were friends than those who were not known at all. It was an obvious similarity, though not so great as to be considered related.
This is not the first time a study has produced a similar result. Already in 2014, other related research by the University of California, pointed out that many couples of friends had a genetic similarity of 1%. Although, according to this other study, that percentage of genetic similarity would be similar to the one you can have with a distant cousin.