How friendships evolve: being alike may matter more than being related
By Ruth Thomsen
A half century ago, Hamilton (1964) attempted to explain the conditions surrounding the evolution of social behaviours. To enhance direct and indirect fitness individuals should adapt their behaviours towards conspecifics based on the degree of genetic relatedness in a way that the stronger they are related the more they should cooperate and the less they should fight against each other.
Obviously, Hamilton's unspoken assumptions were that kin always is reflected in the phenotype of individuals in a way that the closer related individuals are the more they look, smell or sound alike, and further, that animals are somehow (!) able to detect relatives (!!). Although dozens of studies following Hamilton's idea are published true empirical proofs that relatedness really and always is expressed in phenotypes are missing, so far.
In contrast, in humans and nonhuman primates non-related individuals cooperate with each other as well - a pattern that actually is mysterious for all Hamilton followers, and thus remains widely ignored. To explain such friendships the method of choice is to test whether at least some of the friends are more alike in their phenotypes (i.e., faces, voices, odours) than related individuals. If so, Hamilton and his followers are wrong.