A recent study by researchers at UC San Diego and Yale found that friends are closer to family than you might imagine. They have more DNA in common with one another than with strangers. Yet, these friends were not biologically related.
Put differently, we share genetic similarities with our friends that we do not share with strangers. The researchers found a 1 percent genetic similarity among friends, the same degree of similarity to be found among fourth cousins. Similarities were closest among genes that affect our sense of smell.