greg cochran says (or writes, i guess — unless he talks to his computer monitor like some of us people do…):

“If a new environment favored lower (or higher) aggressiveness in males, a Y-chromosome that induced lower (or higher) aggressiveness would take off. And since different Y chromosomes do indeed affect the level of aggressiveness in mice [which I just found out], possibly by affecting testosterone production – this mechanism is plausible….

“Fortunately for all concerned, the selective value of aggressiveness, etc. has been the same for all human populations forever and ever, before and after the development of agriculture. Otherwise you might see weirdly rapid expansions of particular Y-chromosome haplogroups – common, yet only a few thousand years old.”

i nominate as one such example of this selection that never happened the “YCAII=22-22 and DYS388≥15” cluster of haplogroup J-M267 which, depending on who you read, may or may not be related to the arabs’ expansion out of their peninsula in historic times. whatever the full story, haplogroup J-M267 certainly looks arab-expansiony:


hage and marck have shown how mating patterns can affect the distribution of sex chromosome haplogroups (mmmm-hmmm!). the prevalence of father’s brother’s daughter’s (fbd) marriage amongst the arabs could certainly have had an effect on the successful distribution of the J-M267 haplogroup, especially the YCAII-whatchamacallit cluster mentioned above if it was really connected to the arab expansion.

remember that fbd marriage concentrates y-chromosome types into these patrilineages, so fathers, sons, grandfathers, paternal uncles, paternal nephews, paternal male cousins, etc., all share the same y-chromosome (barring variations due to mutations, of course):

parallel cousin marriage

of particular interest is how men (“C” in diagram above) ensure that their male grandchildren by their daughters (“E” in diagram above) also have their y-chromosome, ’cause they marry their daughters off to their paternal nephews (i talked about that here). this doesn’t happen in most marriage systems. so, really, ALL the males in (ideal) arab, fbd patrilineages share the same y-chromosome.

this is one way that inbreeding could serve to accelerate the acquisition of “genes for altruism” in a population. if, say, those genes were aggression genes on the y-chromosome — genes that led to altruistic behaviors in the sense that the individuals having them were more likely to “kill thy unrelated neighbor” and make life better for themselves and their own — then inbreeding, especially father’s brother’s daughter’s marriage, could help those genes pile up more quickly.

(note: comments do not require an email. arab thoroughbred.)