Genetics and Friends: Shared Genes and Shared Good Times

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Friends share more genetic material than non-friends, according to a new study. Humans are social creatures and the tendency is for people to form friendships with people who are similar to them. This study showed the similarity extends to the level of genetics.

The title of the study report is Friendship and Natural Selection and the researchers aim was to take a look at friendship from an evolutionary point of view. The authors offered the suggestion that maybe friendships are formed to create “functional kin.”

The study was carried out by Nicholas A. Christakis and James H. Fowler who are at Yale University and the University of California at San Diego, respectively. The study report was published in the journal The Proceedings of the National Academy of Sciences.

Data from the Framingham Heart Study was used. The Framingham Heart Study is a very famous study that was initiated in 1948 to study risk factors for cardiovascular diseases. Residents of Framingham, MA were the subjects in the study and they were followed for decades. The results of the study laid the basis for cholesterol being thought of as an important factor is risk for heart disease.

The research employed genome-wide analysis and so looked at the genome on a nucleotide level. The total number of single-nucleotide polymorphisms (SNPs) that was analyzed was 466,608. The total number of subjects was 1,932 and they were in one or more of 1,367 friendship pairs. The researchers took care that the friendship pairs did not include anyone that was biologically related. They also established a cohort of subjects that were strangers. Pairs of strangers were randomly determined and 907 stranger pairs were established.

Friend versus stranger pairs were compared. The analysis showed that friend pairs shared approximately 0.1 percent more of their DNA than the stranger pairs. This genetic similarity was at the level of the genetic similarity for fourth cousins.

A criticism of the study is that ethnicity and education level were not controlled for. These factors are likely to play a role in how people meet and form friendships. Since the genetic data came from the Framingham Heart Study, which means the data came from people who were living in this small community, unknown biological relatedness could be a confounding factor as well. Another consideration is people tend to prefer certain environments over others and people that enjoy spending time in their “chosen” places are more likely to form friendships with each other.

The results from the study are to be considered in the context of natural selection, which means there should be some selective advantage to making friends with people who are more genetically similar. The authors state that it is well-known that people tend to form friendships with others that they look like. Since physical traits have a genetic basis, friends should therefore have more genetic similarity. The results from this study, however, showed that there is genetic variability on the level of SNPs. Friends share good times and it seems that they tend to share genes as well.

By Margaret Lutze

Sources:

PNAS
BBC News
CBS News

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