Friends Nhama Mane (L) and Suncar Darame pose in matching
outfits in the Mistra district of Bissau. A new study shows
that people are apt to choose friends who are genetically
similar to themselves. REUTERS/Joe Penney/Files
The truism that friends are the family you choose may be
more accurate than you might suppose.
A study published this week found that people are apt to pick
friends who are genetically similar to themselves - so much
so that friends tend to be as alike at the genetic level as a
person's fourth cousin.
The findings were based on an examination of about 1.5
million markers of genetic variations in a group of nearly
2000 people who had taken part in a long-running health study
based in Massachusetts. The researchers compared people
identified as friends to those who were not.
The study showed people were most similar to their friends in
olfactory genes, which involve the sense of smell, and were
least similar in relation to immune system genes.
"Olfactory genes have a straightforward explanation: People
who like the same smells tend to be drawn to similar
environments, where they meet others with the same
tendencies," said one of the researchers, James Fowler, a
professor of medical genetics and political science at the
University of California, San Diego.
The study, published in the scientific journal Proceedings of
the National Academy of Sciences, follows research released
in May that found that people tended to choose spouses who
have similar DNA.
Fowler said the new findings made it clear that people have
more DNA in common with those who are selected as friends
than with strangers in the same population. Fourth cousins
are people who have great-great-great grandparents in common.
Because the study population was largely homogeneous, mostly
whites of European background, the findings "are less likely
to be driven by the simple explanation that people of similar
ancestry befriend one another," Fowler said.
Fellow researcher Nicholas Christakis, a Yale University
professor of sociology, evolutionary biology and medicine,
said the mechanism used by people to choose friends with
similar genetics remained a mystery.
"It could involve the workings of a postulated 'kin detection
system' in humans," Christakis said. "Our fates depend not
only on our own genes, but also on the genes of others around
us, and in particular our friends."
Christakis said he was interested in finding out why people
have friends in the first place.
"The making of friends is exceedingly rare in the animal
kingdom," Christakis added. "Certain other primates,
elephants and whales are the only other mammals who do this,
and this alone aroused our curiosity."