Cultural selection….

By Razib Khan | February 25, 2007 1:21 pm

John Emerson has a long post about the relationship between irrationality and the emergence of new cultural forms. Worth reading. The other day I had a thought: many cultural traits are basically hitch-hiking along. Consider circumcision and the ban against pork consumption for Muslims, in places like Indonesia when tribes convert to Islam they abandon their pigs and circumcision becomes the norm. Why? People have been inventing strange functional rationales for these customs for decades. It seems likely that these practices have a role as ingroup vs. outgroup markers, that is, they’re convenient shibboleths. Food taboos of course impose segregation between different groups if they can’t eat together without transgressing their norms (e.g., Muslims eating at a Chinese house often have issues because of the ubiquity of pork). That being said, an interesting model for the “selection” of shibboleths is that the group in which cultural form or religion x arose tend to serve as a model, and so all sorts of peculiar customs spread outward. For Islam, circumcision and the non-consumption of pork would qualify (circumcision is actually not even a religious sacrament in Islam as it is in Judaism, but simply a custom which has become accepted through consensus as defining a Muslim male). The spread of Roman-Christian culture in Europe had the same effect, Romanitas entailed the spread and adoption of customs and traditions which were not central to the civilizing aspect of literate Mediterranean culture.

  • Salad Is Slaughter

    I’ve always wondered if dietary rules came about due to bad preparation or food allergies. Someone didn’t cook their pig enough, got trichinosis, and died. Another person who was allergic to shellfish met the same fate. Obviously the local god disapproved of this food and smote the diners.

  • Colugo

    You’re right, but you’re also reinventing the wheel.
    Cultural Selection and Genetic Diversity in Humans. Whitehead, Richerson, and Boyd. 2002. Selection. 3(1), 115-125.
    “When neutral or nearly-neutral genes and selectively advantageous cultural traits are being transmitted in parallel (“symmetrically” in the terminology of Boyd and Richerson 1985) genetic diversity may be reduced by this process which has been called “cultural hitchhiking” (Whitehead, 1998) as it is analogous to genetic hitchhiking (in which a selectively advantageous gene reduces the diversity of its linked neighbor; Maynard Smith and Haigh, 1974).”

  • razib

    yeah, i assumed so. i haven’t read richerson & boyd that closely….

  • Colugo

    Have you read William H. Durham’s ‘Coevolution: Genes, Culture and Human Diversity’ (1991)? It’s a great resource, with case studies (sickle cell, lactose absorption etc.) and a review of gene-culture evolution theories.

  • razib

    no, i’ve seen it referenced. i’ll push it up the ‘must read’ queue.

  • John Wilkins

    Both sources are here referring to the effects on genes of cultural selection. There’s another way to conceptualise this (which is often unfortunately tied into memes as cultural genes) – the selection here is on hitchhiking cultural elements, independently (sort of – Durham really is good on this) of genes. There are no “Muslim genes” that are either swept along with Muslim doctrines and practices, or eliminated when pigs are kept (even though Islam begins as an Arab religion, and tends to make Arab genes, if such exist, able to spread with the religion).
    Boyd and Richerson propose both vertical (genetically linked) transmission and later transmission. This is not necessarily genetically linked, in that while populations tend to be genetically related, ideas can be passed on to non-kin, and yet undergo the same selection pressures as those that are passed on to kin.

  • Colugo

    John Wilkins:
    I don’t have a problem with the term “meme” myself, as long as we are clear about what we are discussing; same with “gene”. I agree with RPM’s sophisticated context-specific approach to “gene” rather than more rigid, exclusionary, and limited ones (e.g. Larry Moran’s definition).
    This article discusses a kind of hitchhiking more relevant to Razib’s speculation than the 2002 article I cited:
    Style, Function, and Cultural Evolutionary Processes. With Robert Bettinger and Robert Boyd. In: Darwinian Archaeologies, Herbert D.G. Maschner (ed.), New York, Plenum, 1996, pp. 133-164.
    Richerson’s page of downloadable articles.

  • bigTom

    I think picking circumcision was a poor choice. I think it is generally considered in medical circles to reduce the spread of sexually transmitted disease. In the case of HIV, they claim the transmissability reduction is a little more than 2x, i.e. we should be promoting the proceedure for public health reasons.
    I suspect a lot of practices that got incorporated into religious dogma were originally based upon astute observations. Group X practices Y, and we see that they are more likely to get sick -ergo god disapproves of Y. I don’t know what the dangers of eating pork are, perhaps some biologists can come in here, but perhaps eating pork in the seventh century was associated with increased risk of illness.

  • razib

    I think picking circumcision was a poor choice. I think it is generally considered in medical circles to reduce the spread of sexually transmitted disease. In the case of HIV, they claim the transmissability reduction is a little more than 2x, i.e. we should be promoting the proceedure for public health reasons.
    1) HIV as a selective pressure hasn’t been around for thousands of years everywhere (circumcision is practiced in many different cultures, including isolated ones such as is in australia).
    2) the benefit of circumcision is contextual. japan is uncircumcised, south korea is, and both have about the same (very, very, low) HIV infection rates. circumcision, obviously, tends to return value when HIV rates are already pretty high.
    3) you might say that this is relevant to ancient venereal diseases. quite possibly, but, please note that
    a) circumcision in premodern times was likely not as extreme in removal of the foreskin as it is today because of more primitive surgical techniques. so its protection would not have been as great. observe that female circumcision is robust common throughout much of africa where male circumcision is common despite its obvious fitness (negative) implications.
    b) note the part about surgical procedures: premodern circumcision was not characterized by sterilized hospital rooms, i am willing to bet that the risk from infection after the initial cut was significant enough to cancel out later benefits.
    4) we have a case study of a minority population in the ancient world that was circumcized, the jews. some estimates put that at 10% of the roman population. most non-jewish romans were not circumcized (though some populations in the levant and egypt were also likely cut). in fact, christianity’s rejection of circumcision as mandatory for males was one of the major breakpoints between it and judaism. the percentage of jews declined in the ancient world after the rise of christianity, in large part possibly because of the conversion of hellenistic jews to christianity. these jews abandoned circumcision obviously, and so the frequency of this practice and jews decreased within the empire. my point is that a naive narrative of circumcision = greater fitness seems ludicrous. the decline in the % of jews had nothing to do with circumcision, but the fact that non-circumcized christians and pagans increased in numbers at jewish expense shows that its fitness boost is minimal (and the pagans & christians did not adopt this practice from the jews, or other circumcized populations).
    5) china has long has a circumcized muslim minority among its non-circumcized han majority. again, we see here no long term fitness benefits of a minority.
    6) re: pigs, the argument has been made that uncooked pork tends to spread trichinosis. this is post facto rationalization. exactly how many pigs were being raised in pagan arabia??? note: pigs are not creatures that do well in very dry & hot climes. so the ban against pork consumption seems pretty ridiculous when you hardly have any pigs to eat in the first place (the problems with pigs and infections from undercooked meat can be generalized to almost all meat).
    one can weave almost any functional story out of a cultural difference. but their selective impact is likely to be marginal when extracted out of their cultural context.

  • David Boxenhorn

    I, too, have often thought about cultural hitch-hiking. I think that one of the best examples is western music.

  • outeast

    pigs are not creatures that do well in very dry & hot climes. so the ban against pork consumption seems pretty ridiculous when you hardly have any pigs to eat in the first place
    Hmm. Jesus banished an evil spirit into a bunch of pigs or something, didn’t he? So they can’t have been exactly unheard of in the Middle-East… I’m not sure what their function was, though: who was eating them? Not the jews; the Romans? The Arabs? Was Jesus buggering up some poor Arab swineherd’s livelihood?
    Wikipedia has the following note: ‘Maimonides, the Jewish court physician to Muslim sultan Saladin in the twelfth century, agreed with other Muslims and Jews of his day by declaring that pork was an “unclean” meat because of pigs’ dirty habits; when pigs cannot find water, which is often the case in the Middle East, they have to bathe in mud or their own feces. Maimonides therefore asserted that pork was an unhealthy and unwholesome meat to consume. He was the first to justify the taboo on secular rather than religious reasons.’
    This does seem to concur with Razib’s claim that there is little reason to believe that the Jewish (and hence Islamic) prohibition of pork was due to trichinella. Bear in mind, too, that Leviticus does not mention worms: instead, pork is banned because pigs ‘divide the hoof, and be cloven footed, yet cheweth not the cud’. Which don’t sound like no medical reasoning to me.

  • Colugo

    Marvin Harris had an adaptive explanation for Middle Eastern pig taboos. Like humans, pigs are omnivores that cannot eat grass. In the arid Middle East pigs are effectively competing with humans for food, unlike the situation in Europe and China. Because raising pigs was a poor and risky investment in that region, pork taboos ensured that such a mistake would not be made.
    Of course, an adaptive trait in one ecosystem may be a neutral or maladaptive one elsewhere, where it is hitchhiking rather than directly selected for.
    Male circumcision: A number of theories, some involving Zahavi’s handicap hypothesis, some not.
    Richard Sosis publication page: signaling and ritual
    Sosis, Richard, Howard Kress, and James Boster Scars for War: Evaluating Alternative Signaling Explanations for Cross-Cultural Variance in Ritual Costs. Evolution and Human Behavior. (forthcoming)

  • John Emerson

    Marvin Harris can be interesting and fun, but he is very Just So Story-ish.
    Under similiar circumstances pigs might just as well become an elite luxury food.
    A lot of food taboos have to do with refusing to eat meat sacrificed to idols — in Buddhism and both in early and early medieval Christianity (among converted Vikings). Harris conjectures the same for the Hebrews (theorizing that pork was a sacrificail meat for Mesopotamians as it still is for Chinese). I haven’t seen Islam interpreted this way, but pagan Arabs might have been pork-eaters — though Muhammed migh just have borrowed the Jewish taboo.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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