there’s some good evidence that, on average, people:

– feel more grief over the death of a child who was most like themselves;

– care more for their grandchildren with whom they share the most genes (at least grandmas do anyway);

– are sexually attracted to individuals with whom they share genes if they don’t experience westermarck imprinting (or is it reverse imprinting?), and are more sexually attracted to those individuals with whom they share more genes.

all of this makes sense from an inclusive fitness point-of-view. on average, people really seem to behave according to the “two brothers or eight cousins” rule.

so i’ve been thinking, if you took two human populations with exactly the same evolutionary histories so that they had all of the same sorts and frequencies of genes — including those for altruism (and other social behaviors) — and then had one of the groups inbreed for a generation or two, the inbred group ought to start being more altruistic/whatever to their family members, on average, simply because they would share more genes with — be more genetically similar to — their family members than the non-inbred group members would be to their family members.

i’m guessing, then, that there are two things going on with inbreeding/outbreeding and altruism/other innate social behaviors:

– genetic similarity within a population directly and immediately affecting how people behave towards one another,
– and the evolution of genes for altruism over the longer term.

greying wanderer is ahead of me on this one (^_^):

“I think altruistic behaviour is the *product* of two separate things: relatedness and altruistic genes multiplied together, so the more related people are the less strong their altruistic genes need to be. If the human default is inbreeding then i think this makes more sense as an inbred group would then only have needed to develop very small amounts of altruism genes to create an altruistic effect. If so then it’s only when people outbreed that they need to develop *more* altruism genes to compensate for the drop in relatedness and it’s this that explains how those people can then come to display altruistic type behaviour towards non-kin.”

i thought before that maybe oubred groups evolved different altruism genes (i.e. ones for reciprocal altruism vs. familial altruism) rather than more altruism genes, but i like g.w.’s idea, too. definitely food for thought!

of course, genetic similarity+inbreeding+altruism is pretty much what steve sailer talked about in “Cousin Marriage Conundrum.” (^_^)

see also j.p. rushton’s genetic similarity theory.

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