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Friendship & Natural Selection - Coggle Diagram
Friendship & Natural Selection
Abstract
Body
Homophilic interactions are positively correlated while heterophilic reactions are negatively correlated
Homophilic reactions may yield a synergistic advantage that has been helping to drive human evolution
A focused gene-set analysis can provide insight into correlations found in specific systems. Olfactory gene sets are homophilic and immune system gene sets are heterophilic
These systems may play a role in the formation or maintenance of friendship ties
Introduction
Humans form strong social bonds to individuals that are not kin. This is more common in the humans than any other organism.
These bonds tend to be with similar people.
There may be correlations between genes shared and how well people connect.
The level of similarities in genotype can be used to create a friendship score between individuals.
Introduction
Homophily
Modern and early humans share regularities in constructed social networks and interactions.
Genes play a role in the formation, attributes and structures of friendship ties.
Social ties indicate the tendency for humans to form ties based on phenotypic similarities.
There are 4 reasons that friends may exhibit homophily in genotypes.
People may choose certain environments and in those environments encounter people with similar phenotypes, influenced by specific genotypes. Even friends chosen at random are likely to have similar genotypes in this case.
Possible by-product of the tendency of people to form bonds with those in close proximity or individuals of the same race. These individuals often share the same ancestry
People may be chosen by third-parties to be in certain environments. In these environments they may interact with people of matching genotypes.
People may actively choose and retain friends of similar genotypes or terminate those with different genotypes.
People prefer to associate with those of similar phenotypes.
Birds of a feather flock together
These mechanisms could operate alone or together.
Heterophily
There are few reasons that heterophily may be exhibited. However, there may be two underlying mechanisms that explain the occurrence of heterophily.
People may actively choose to befriend people of a different type. This is usually for reproductive reasons. Immune system genotype is one such that causes heterophily.
These mechanisms could also operate individually or simultaneously
Certain environments may foster interactions between individuals with dissimilar traits.
Evolutionary implications
Preferences for both hetero or homophily are dependent on the relative fitness advantage of genotypic similarity or dissimilarity.
This varies by trait.
Homophily evolves under a wider variety of conditions even when it is more advantageous to be heterophilic. It is less costly to find a successfully interaction with a similar partner in a population of similar people than it is to interact with someone dissimilar in a dissimilar population.
Hypotheses
There should be more positive selection for homophilic genes amongst friends
Possible "kin detection system"
Our capacity to make friends with unrelated individuals may have contributed to our evolution.
Methods
Kinship coefficient
probability that two alleles samples at random from two individuals are identical.
Positive values indicate that genotypes are positively correlated and negative value indicate that two individuals are not related.
Used to measure homophily
Using genome wide association study techniques to identify theorized patterns across the entire genome.
Analyzed 466,608 single nucleotide polymorphisms in 1,932 individuals. These individuals are in or or more of 1,367 friendship pairs.
Measure heterophily
Measure the empirical probability that two individuals have opposite genotypes at a give SNP.
Results
Friends tend to be more genetically related than strangers. The size of the difference roughly corresponds to the kinship coefficient expected between 4th cousins. **
Friends tend to have fewer SNPs where genotypes are exactly opposite.
Pairs of friends are more homophilic and heterophilic than pairs of strangers
May obscure mechanisms that tend towards heterophily for certain traits.
There are many traits with low levels of homophily. The general levels of correlation of genome-wide association study found in friends can be used to generate a friendship score. This score can predict if two individuals would be likely friends.
Discussion
This experiment did not control for social stratification. Their goal was to characterize overall similarity.
Homophilic SNPs are more likely to be under positive selection.
The genotypes that are shared between friends are more likely to be under recent natural selection.
Genetic structure of human populations are dictated by reproductive and friendship unions.
One's genotype may lead someone to seek out circumstances that are compatible to their genotype.
The field of indirect genetic effects is growing. Phenotypic traits of focal individuals are influenced by the genome of the neighbors.