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Friendship & Natural Selection - Coggle Diagram
Friendship & Natural Selection
Christakis NA, Fowler JH. 2014. Friendship and natural selection. Proc Natl Acad Sci USA. 111(supplement_3):10796–10801. doi:10.1073/pnas.1400825111.
Humans are highly social creatures, and non-relation ties (friendship) may be linked to individual genotypes.
The tendency to form ties with those phenotypically similar to oneself is known as homophily.
Top Four Genetics-Based Reasons for homophily:
Purely by chance due to geographic or ethnic proximity.
Surely there is no social reasoning that can explain why those of similar phenotype would form close bonds.
Certainly not something that is no longer allowed to be taught in Florida public schools...
Homophily can act as a "functional kin" detection system.
If we look alike, then there is a higher probability that on some level we are related, even distantly.
If we are distantly related, bonding with you may increase my indirect fitness in some way.
Humans actively seek friends based on homophily, and break relations based on heterophily.
Acknowledging the geographic/ethnic point, how does that correlate to high frequencies of shared SNPs on site?
Certain populations were localized together by force and found those with similar phenotypes upon relocation.
The environments we find attractive is dependent on genotype.
If areas collected similar genotypes, then of course there would be similar phenotypes in the same area.
Synergy
Aside from one gene with varients that displays homophily and heterophily, all other genes studied by Christakis and Fowler (2014) displayed clear correlations to homophily.
Hypotheses for Pro-Heterophily
The environment may push phenotypically dissimilar individuals together.
I'm great at protecting others. You're great at farming. Together, we make a functional society.
Those with phenotypic differences are just drawn together.
This has been observed: immune system genotypes in mating pairs.
Complementary skills of specializations
Many of these theories overlap within and between these two groups.
Some genetic fitness may show advantages depending on whether other genes are present or absent in the relation hierarchy of the individual.
Homophily tends to arise under a larger range of conditions across more models by Christakis and Fowler (2014).
If a genotype has an advantage, then it is expected to move toward fixation. If the whole population feels this selection the same way, homophily would be expected to rise.
And if some genes have increased selection when paired, positive selection continues to push fixation.
After compairing SNPs of friend ties with SNPs between strangers showed that friends show significantly more relatedness genetically than strangers (p<2x10^(-16)).
Where heterophily was expected, friends tended to show fewer similarities (p=4x10^(-9)).
Homophily has been shown to be more prominent in friends, but there are definitely heterophilic patches at play.
Participants in the study were predominantly Caucasians of Italian descent. Meaning the results may be biased.
Of the genes showing homophily, Christakis and Fowler (2014) checked for gene sets that were overrepresented significantly.
A pathway for the transduction of olfactory impulses showed significant homophily (p=4*10^(-5)).
Metabolic pathways of linoleic acid was also overrepresented in homophily.
Further investigation elucidated that observed homophily in humans was likely only recently under selection pressures.
The major overepresented geneotype heterophilically was immune mechanisms, which was expected.
Genotypes not only influence preferred physical environment, but also the social aspects of one's environment.
This is pushing a new area of study, network epistasis.
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