Consciousness Blog 08 June 2014

It is a matter of common observation that similar individuals tend to mate with each other: my cousin who is six feet four inches tall has a wife who is just on six feet. Short billionaires who marry tall, leggy blondes (there are quite a few of them) are an apparent exception, but money distorts the similarity mechanism as it distorts other mechanisms. On the other hand, some scientists expect to find enhancements to evolutionary fitness resulting from exogenous mating, because it will tend to enlarge the gene pool.

A group of American researchers has now demonstrated a statistically significant predilection for people to mate with genetically similar individuals. The effect is clear, and has been demonstrated to be independent of, although weaker than the established tendency of people to have mates from similar educational backgrounds.

Study leader Benjamin W Domingue of the University of Colorado's Institute of Behavioral Science says that the research, among a population of 825 married couples, eliminated racial variability and controlled for ethnic variability, yet still turned up a preference for genetically similar individuals. Says Domingue: "We do know in some sense that people prefer genetically similar spouses because we know that people tend to date and marry within their own racial and ethnic groups. We worked really hard in this study to not just replicate that fact."

The research compared 1.7 million single-nucleotide polymorphisms (individual DNA building blocks) in reaching its conclusions. Domingue does not attempt to theorize about the exact mechanisms which are involved in creating the effect, calling the process 'complicated and multifaceted.'

That is surely correct, although it would perhaps be possible to isolate the role played by some unique human characteristics such as language and facial expressiveness by seeking a similar effect among non-human primate populations. At all events, we can speculate on the utility of the effect in terms of human groupishness. While some groups of humans did perhaps originate as kin groups, the tendency for groups to form among the members of wider populations, which did and does play a major role in the development of human society, might well be assisted by a tendency to seek genetically similar mates, who would assimilate more readily, it could be argued, into the group of which the pair would become members. Of course, it might be the other way around: that the fact of kin groups would build a preference among their members for genetically similar mates, which would then operate among non-kin populations as well. Both mechanisms may be at work, indeed.

However the effect originated, on its own it would tend to favour consanguineous mating and the generation recessive genes, so you would expect to see it balanced by the tendency towards exogenous mating, and the development of rules against consanguinity in mating behaviour.

Read more in Chapter Three of Agent Human by Michael Bell, The Evolution of Social Consciousness in Humans.


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