the good professor harpending who, unlike me, actually knows what he’s talking about when it comes to population genetics, took a mathematical look at my suggestion (guess!) that there might have been enough time over the medieval period for genetic changes in the population to have resulted in the historical decline of violence in nw europe that pinker described in The Better Angels (see also eisner).

prof. harpending concludes that — yeah, sure — there might’ve been enough time (from the 1300s to the modern period) to effect such a genetic change. it would’ve been a bit of a push, but it could’ve happened:

“In the present case we need a response of 1/28 of a standard deviation per generation. Assuming an additive heritability of 0.5 (the true value is probably 0.8 or so from literature on the heritability of aggressive behavior in children) the selective differential must be about 1/14 or .07 standard deviations per generation. In terms of IQ this would correspond to a one point IQ advantage of parents over the population average and in terms of stature parents with a mean stature 0.2 inches greater than the population average. This would occur if the most homicidal 1.5% of the population were to fail to reproduce each generation.”

no, i didn’t understand most of that either.

i do understand that he thinks he went conservative in his calculation (i.e. using an additive heritability [<< two links there] of just 0.5 although he thinks it's probably more like 0.8), so that might mean that his calculation should actually be even more in the hbd-ist’s favor. in any case, he concludes that natural selection against “genes for violence” (or selection for “genes for nonviolence”) could explain the historical decline of violence in nw europe “if the most homicidal 1.5% of the population were to fail to reproduce each generation.” a bit of a push, maybe, but possible. (if they really did fail to reproduce.)

he suggests:

“Justice was famously brutal and harsh in Medieval and Renaissance England so this may not be an entirely meaningless exercise. In this excellent essay Peter Frost suggests that the nearly the same selection against violence occurred in the several centuries before the fall of the Roman Empire, and he provides grisly details of Roman treatment of criminals.”

that is one route to go — have the state simply remove the bad guys out of the gene pool.

i’d like to suggest another route (and this is where i’m going to start sounding like a broken record): that they got rid of clannishness in medieval nw europe.

why should getting rid of clannishness matter? because, for whatever reasons (i think the reasons are connected to inclusive fitness), clannish people are violent. blood feuds, honor killings, general obstreperosity — clannish people are just not peaceful.

why? i think it’s ’cause clannish populations are inbreeders and inbreeding alters the possible inclusive fitness payoffs. if you’re from an inbred group, you don’t have to stick your neck out for two brothers or eight cousins to increase your inclusive fitness. if your group is inbred enough, you might only have to be altruistic (in the biological sense) to just one brother or only four cousins (’cause you share that many more genes with your inbred relatives than individuals in an outbred population would, capiche?).

in an inbred population, violent clannish behaviors — which are just the flip-side of being altruistic towards one’s relatives (i.e. be really un-altruistic towards one’s un-relatives) — would/could quickly be selected for since the inclusive fitness payoffs are greater for each altruistic act. and this is exactly what wade and breden (1981) found: inbreeding can accelerate the selection for altruism genes (see also here).

so, to get rid of violence, you could get rid of clannishness. and to get rid of clannishness, you need to get rid of inbreeding. which is exactly what happened in medieval europe starting in the early part of the period. the roman catholic church, supported by secular authorities, banned cousin and other close marriages beginning in 506 (i think that’s when the first ban on cousin marriage was laid down).

enforcement of the various cousin marriage bans, which ranged from first to sixth cousins depending on what century you’re talking about, wasn’t easy — at least not in the beginning. the church, for instance, didn’t require that a marriage ceremony take place in a church until something like 1000 or 1100, so enforcement by the church in the early middle ages was probably patchy at best. however, there were LOTS of secular laws throughout nw europe banning close marriage, including very much so in anglo-saxon england. just a couple of examples: the law of wihtred from the 690s outlawed cousin marriage — and the punishment for cousin marriage in another anglo-saxon law from sometime the 900s-1000s was slavery for the perpetrators. again, difficult to know how well these laws were enforced; but that there were plenty of such laws indicates that the authorities were keen to do something about all this close marriage.

the law of wihtred is, i think, the earliest anglo-saxon law that i’ve come across which made cousin marriage illegal (at least in the part of england where the law of wihtred applied). so the push against inbreeding in anglo-saxon england started at least as early as 690 a.d. again, it may not have been very effective at that point, but england’s outbreeding project had begun by that point.

lorraine lancaster, still considered the authority on anglo-saxon kinship, concluded that, although its importance was beginning to wane (as indicated by a shift in who would be awarded wergeld in the event of a crime against a person, that person’s kinsmen or their guild), an individual’s extended kindred remained of importance in anglo-saxon/english society well into the 1000s. that suggests to me that “clannishness” was still around in the 1000s in england. feuding was definitely still a regular event.

the situation had changed quite a bit by the 1300s when nuclear families were all the rage and englishmen no longer relied so extensively on their extended families. people were still violent in 1300s england, but of course the shift from clannishness to non-clannishness — i.e. from violence to non-violence — would’ve taken some time. evolution doesn’t happen overnight.
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the state’s monopoly on violence and outbreeding don’t have to be mutually exclusive explanations for why there may have been a genetic change in nw europeans leading to a decline in violent behaviors. the answer might be both. like jayman said

“Inbreeding, and hence clannishness, can interfere with this process, because while the State is selecting for less violent people, clan conflict presents a counteracting selective pressure for people who are more violent (and can fight feuds).”

…so in places where inbreeding has not abated or did not abate as early as in england — the arab world/middle east, china (or parts of it anyway — h/t luke!), the highlands of scotland, the auvergne — the state hasn’t managed to quell violence as easily. the combo of outbreeding + an effective state seems to be a winning one. better yet if you don’t need such a very strong state (modern nw europe) and the population is just non-violent naturally.
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this is all just a theory, of course — theory with a small “t”. but, as cochran and harpending have said (h/t kiwiguy!):

“Whereas tests of hypotheses ought to be careful and conservative, generation of hypotheses ought to be speculative and free-ranging.”

so there! (^_^)

there ought to be a way of mathematically modelling my suggestion — i.e. that the historical decline of violence in nw europe is at least partially the result of the de-selection (if you can say that) of “genes for violence” due to a reduction in inbreeding — but since i’m pretty much numerically illiterate, i won’t be the one working up those models. i would think, though, that in addition to using the breeder’s equation in the calculation, you’d also want to factor in inbreeding/outbreeding somehow.

see also: Genetics and the Historical Decline of Violence?

previously: what pinker missed and “violence around the world” and outbreeding, self-control and lethal violence

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