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(CNN) -- This brings a whole new meaning to the
phrase, "You've got a friend in me."
A new study published Monday in Proceedings of
the National Academy of Science suggests friends
may be more than just people you lean on when
you're not strong; they might actually help you
carry on -- genetically speaking.
"Looking across the whole genome, we find that
on average, we are genetically similar to our
friends," said James Fowler, coauthor of the study
and professor of medical genetics and political
science at UC San Diego. "We have more DNA in
common with the people we pick as friends than
we do with strangers in the same population."
Over the past decade, Fowler and coauthor
Nicholas Christakis, professor of sociology,
evolutionary biology and medicine at Yale, have
studied the science behind social networks.
They're seeking a biological explanation behind
some long held social notions.
"We've all heard the phrase, 'Birds of a feather
flock together,' but we want to know why,"
Fowler said.
Using data from the Framingham Heart Study, the
researchers were able to conduct what they say
is the first genome-wide analysis correlating
genotypes between friends.
According to the U.S. Department of Health and
Human Services, the Framingham Heart Study
started in 1948. It is a long-term,
multigenerational study, designed to identify
genetic and environmental factors influencing the
development of cardiovascular and other
diseases. The generational genetic data provided
by the Framingham Heart Study made it an ideal
starting point for Fowler and Christakis.
The study contained 1,932 subjects. One group
consisted of pairs of unrelated friends, while the
other group was composed of unrelated strangers.
Scientists examined 1.5 million markers of gene
variation to accurately measure the genetic
degree to which each person was similar to his or
her paired friend or stranger.
"We have found that we share about 1% of our
genes with our friends," said Fowler. "On average
our studies indicate we are as genetically similar
to our friends so much as we are our with our
fourth cousins or people who share great-great-
great grandparents."
Of the genes most prominently expressed between
pairs of unrelated friends, the researchers found
that the olfactory system genes were
overrepresented.
"Friends tend to smell things the same way," said
Fowler. In prehistoric days, for example, people
who liked the smell of blood might hunt together,
whereas gatherers might prefer the smell of
wildflowers. Nowadays, Fowler says, that
translates into people who like the smell of coffee
congregating at coffee shops.
Researchers say that our DNA could be a driving
force behind the activities we are drawn to and
the social activities we engage in. As such, we are
more inclined to interact and foster friendships
with people who are genetically similar.
Also, the genes that we have in common most
with our friends, are also under the most rapid
evolution. They seem to be evolving at a rate
faster than our other genes, the researchers say.
"Social networks may be turbo charging
evolution," said Fowler.
"Not only with respect to the microbes within us
but also to the people who surround us. It seems
that our fitness depends not only on our own
genetic constitutions, but also on the genetic
constitution of our friends," said Christakis.
Conversely, researchers also found that the
people we choose to associate with tend to be
immunologically different, which may offer us
extra immunological protection. This supports
past research that found spouses tend to have
different immune system genes.
"There may also be advantages to
complementary rather than synergy when it
comes to immune system function," said Fowler.
"You don't want to be susceptible to disease that
your spouse or friend is susceptible to. You want
to be immune to those diseases because it could
provide an extra wall of protection so they don't
pass them on to you."
This study, researchers say, also lends support to
the view of humans being metagenomic --
meaning we're not only a combination of our own
genes but of the genes of the people with whom
we closely associate.
"Most of the study of genetics has been one gene,
one outcome," Fowler said. "I think this is going
to completely change the way we think about
genetics. We have to look beyond ourselves."
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