Wednesday, September 7, 2011

Genes and Friendship

Image 1: Friends Cast Members

Image 2: Brain and DNA Double Helix

Researchers at the University of California have recently discovered a possible association between friendship and the genetic make-up of individuals’. It has for some time become apparent that the Dopamine receptors located in the pituitary gland and central nervous system influences human behavior; however Professor James Fowler and his team, have accomplished to home in on one particular gene, the Dopamine Receptor D2 (DRD2) gene to explain the human process of choosing friends and forming friendships at an allelic level.

According to Professor Fowler et al. (2010), his team isolated six genes (DRD2, DRD4, CYP2A6, MAOA, SLC6A3, and SLC6A4 gene) and analysed genotype samples from saliva for a total of 9,237 subjects to test for genetic relationships between friends1. These subjects were required to give information about their social networks and were controlled for heritable similarity as a result of race, age, gender, environmental association and family ties1.

Results indicate people were generally friends with those who possessed the DRD2 gene encoding if they themselves had it too. The same occurred for friends who did not have DRD2 gene, confirming the phenomena of homophily, “birds of a feather flock together”, where friends developed relationships with those whom they were genetically similar to1. The DRD2 gene was particularly noteworthy, with Dopamine being a vital neurotransmitter which has the ability to control functions such as cognition, emotion and locomotion2. Dopamine receptors are G-protein coupled receptors responsible for stimulatory and inhibitory functions2. The DRD2 gene focused on in this study was located at chromosome 11 (11q22-23) and inhibits adenylyl cyclase2.

Image 3: Molecular Location of DRD2 Gene on Chromosome 11
Interestingly, the event of heterophily was also found to occur with individuals who had the Cytochrome gene, CYP2A6 also known to be responsible for an extroverted personality and involved with the Serotonin hormone pathway1. These subjects were likely to become friends with those who did not have the gene1 – a case where “opposites attract”. An example of this would be people with leadership qualities would be most compatible with people who prefer to be a “follower”. As indicated by Fowler et al. (2011), the data shows that friendships do not develop merely due to similar activities1 e.g. studying the same biology course at university.

The findings of this study is beneficial to society as it shows that niches in friendship groups could affect evolutionary processes for specific social behaviours and even physical health1. For example, pathological immunity to certain infections or pandemics could be caused not solely due to direct environment but in fact, the people individuals are more likely to interact with and thus those who possess specific or similar genotypic patterns1. The fact that Professor Fowler focused on only 6 genes questions the validity of this study, therefore a genome-wide analysis would provide clearer evidence.

Homophily and heterophily phenomena provides insight to geneticists and behavioural scientists with a better understanding of the formation of social networks, human relationships and genetic evolution. Maybe our “friendship genes” are an evolutionary mechanism that contributes to Darwin’s theory of “survival of the fittest”? Nevertheless, it is observed that genes have the ability to influence our environment by impacting on human social behaviour.

Julia Zin (42652016)

Primary source article:

1. Fowler J., Settle J., & Christakis N., 2011, Correlated Genotypes in Friendship Networks, Proceedings of National Academy of Sciences (PNAS), no. 5, vol. 108, Available from:

Useful supporting perspectives & information:

2. US National Library of Medicine (Genetics Home Reference: DRD2) [Internet]. 2011 [updated 2011 Sep 5; cited 2011 Sep 7]. Available from:


3. Friends Cast Members (College Cures) [image on the internet]. 2011 [updated 2011; cited Sep 10. Available from:

4. Brain & DNA Double Helix (NIA Genetics of Alzheimer’s Disease Data Storage) [image on the internet]. 2010 [updated 2010 May 14; cited 2011 Sep 4]. Available from:

5. Molecular Location of DRD2 Gene on Chromosome 11 (US National Library of Medicine) [image on the internet]. 2011 [updated 2011 Sep 5; cited 2011 Sep 7]. Available from:

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