Study finds friends are genetically similar

Date: Jul-15-2014 A new study gives cause to reflect on the saying, "friends are the family

we choose." Researchers at the University of California-San Diego and Yale University in New

Haven, CT, find that friends who are not related biologically have more DNA in common with each

other than with strangers.

Writing in the Proceedings of the National Academy of Sciences, James Fowler,

professor of medical genetics and political science at the University of California-San Diego

(UCSD), and Nicholas Christakis, professor of sociology, evolutionary biology, and medicine at

Yale, describe how they conducted a genome-wide analysis of nearly 1.5 million markers of gene

variation using data from the Framingham Heart Study.

The closest of friends: researchers find that friends who are not related have more DNA in common with each other than with strangers.

Prof. Fowler says, "Looking across the whole genome we find that, on average, we are

genetically similar to our friends. We have more DNA in common with the people we pick as friends

than we do with strangers in the same population."

The authors picked the Framingham Heart Study's data set because it is the largest study they

are aware of that has the level of genetic detail necessary for such an investigation, together

with information on who is friends with whom among the participants.

From the data, they were able to pick out nearly 2,000 individuals and compare pairs of

biologically unrelated friends with pairs of unrelated strangers.

The other thing that is useful about sourcing the data from the Framingham study is that

nearly all the participants are of European extraction. This is normally a disadvantage in

research, but in this case it is an advantage because it rules out a potential bias - that we

tend to choose friends with a similar ethnic background to our own.

The researchers were also able to rule out ancestry, using the most conservative techniques

currently available.

Prof. Fowler says their results are "net of ancestry" and go beyond what you would expect to

find among people of shared heritage.

Friends are the genetic equivalent of fourth cousins

The study shows that, on average, friends share about 1% of their genes - this about the same

overlap as we can expect to find among fourth cousins - that is, relatives who have the same

great-great-great grandparents.

Prof. Christakis says while 1% may not sound like much to most people, to geneticists it is a

significant number. He describes the result as "remarkable," in that:

"Most people don't even know who their fourth cousins are! Yet we are somehow, among a myriad

of possibilities, managing to select as friends the people who resemble our kin."

The authors describe how it makes sense to have these shared genes - they confer various

evolutionary advantages. For instance, for our earliest ancestors, having a friend who felt

cold when they did and built a fire will have benefited both of them.

Prof. Fowler says there is also a kind of social network effect, in that having a trait may

only work if others also have it. Take, for example, the first mutant to speak. They needed someone

else with a similar mutation to converse with.

Friends are most similar in genes controlling sense of smell

The findings show that among friends, the biggest difference was found in genes that control immunity or ability to protect against disease - which may prevent disease from spreading among the group.

As well as looking at average similarities across the genome, the two scientists also looked

more closely at particular sets of genes.

They found, for example, that friends are most similar in genes that control the sense of

smell, and most different in genes that control immunity or ability to protect against

disease.

Again, the authors see an evolutionary explanation for the immunity finding - having

friendships with people whose genes protect them against a different range of diseases reduces

the risk of a disease spreading in the group.

This finding is similar to previous studies that have the same effect in spouses.

But how are we selecting friends based on differences in immunity and similarity in ability to

smell? That is still to be discovered, says Prof. Fowler, who suggests one explanation for the

sense of smell finding is that our sense of smell means we gather in similar environments - take

coffee houses, for example. However, the authors say the underlying biology is likely to go

further than that, and further studies will probably show a number of mechanisms are involved,

working together and in parallel.

Genes similar between friends are evolving faster than other genes

Another surprising finding was that the genes that seem to be more similar between friends

appear to be evolving faster than genes that are not. Perhaps this explains why human evolution

appears to have gone faster in the last 30,000 years than previous to that. The social

environment could also be a reason, say the authors.

Prof. Christakis says the study also supports the idea that humans are "metagenomic," that is, our fitness to survive depends not only on our own genes, but that of friendly organisms inside

us (our gut microbes, for instance) and around us, such as the genes of our friends.

Funds from the National Institute on Aging and the National Institute for General Medical

Sciences helped finance the study.

Meanwhile, Medical News Today recently learned of another surprising genetic study

where researchers have developed a computer algorithm that can diagnose rare genetic disorders

from photographs of children.

Written by Catharine Paddock PhD

View all articles written by Catharine, or follow her on:

Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.