Why culture is chunky and genes are creamy

By Razib Khan | February 6, 2013 2:24 am

My daughter has four grandparents. Genetically she is a little over 25 percent her paternal grandfather and maternal grandmother, and a little under 25 percent her maternal grandfather and paternal grandmother.* Why? Because she is 50 percent genetically identical by descent with her mother and likewise with her father. This is all rather straightforward. But what about culturally?

With biological heredity we can speak of genes, the substrate by which inheritance occurs. With culture memes have been far less fruitful as anything more than an illustration, as opposed to the basis of a formal system of logic and analysis. Nevertheless, we can describe with relative clarity many aspects of culture as a trait or phenotype. And this is important. Recall that evolutionary process was characterized by Charles Darwin despite lacking a satisfying theory of inheritance.

One of the more fascinating aspects of surveying human phenotypic variation is that one can consider the differing dynamics which those which are genetically controlled, at least in part, are subject to in contrast to those which are entirely “memetic” in character. Variation in skin color, for example, is mostly genetically controlled. In other words, skin color is a heritable trait in a genetic sense. In contrast the language one speaks is a function of milieu. One’s hair form, blood type, and nose shape, are matters contingent upon one’s biological parents in a necessary and determinative sense. Language, religion, and culinary preferences are accidents contingent upon one’s parents’ preferences.

But it doesn’t end here. In sexual organisms genetic inheritance is symmetric (the autosomal genome has equal contributions from both parents), and exclusively vertical (parents to offspring). In contrast cultural inheritance can be asymmetric (i.e., one inherits by and large the culture of one parent) and horizontal (one inherits the culture of one’s peers). In The Nurture Assumption Judith Rich Harris relates the story of cultural continuity in elite British boarding schools. For generations norms and folkways were transmitted from older students to younger ones, with no parental input. This regular and systematic inter-quasi-generational horizontal transmission illustrates flexibility of cultural transmission which has few parallels in biological genetics. One reason that the logic of biological genetics is powerful is that the system is straight-jacketed by is own constraints, reducing the space of inferences and narrowing one’s extrapolations. Often complexity breeds intractability (see: economics). This is why a formal and systematic study of cultural evolutionary process analogous to that in biology has been a quixotic quest (promoted periodically by individuals of note such as E. O. Wilson and L. L. Cavalli-Sforza, and pushed forward by Peter Richerson and Robert Boyd and their students for several decades).

And yet all this is the broader purview of a paper in Proceedings of the Royal Society B. It is not online as of yet, so I will point you to the report in NatureGenes mix faster than stories. Here is the top line result:

If folk tales simply spread by diffusion, like ink blots in paper, one would expect to see smooth gradients in these variations as a function of distance. Instead, researchers found that language differences between cultures create significant barriers to that diffusion.

These barriers are stronger than those for the exchange of genes — a message that might be crudely expressed as: “I’ll sleep with you, but I prefer my stories to yours.”

The irony here is that despite the powerful flexibility of cultural transmission, quite often it is cultural variation which exhibits sharp inter-group differences. Both common sense and population genetic theory support this finding. Without inquiring further into the matter I will assert, and be willing to take a $100 bet, that the genetic distance between the Flemish and Walloons of Beligum is smaller than that between the Walloons and Catalans. The language of the Walloons is clearly more closely related to other Romance dialects than that of their Flemish neighbors (go to Google Translate and listen to various Germanic and Romance languages with the same phrase, and it is obvious). But it does not follow that this cultural resemblance must entail a genetic resemblance.

As far as population genetics goes, gene flow is a very powerful force in equilibrating allele frequencies. Only 1 migrant per generation is needed between two populations to prevent them form diverging. Even a 1 percent admixture between two populations will quickly equilibrate allele frequency differences, especially considering that on most loci those differences are not of the disjoint character (frequency 0 vs. 1). Continuous gene flow defined by isolation by distance is a constant homogenizing force across adjacent populations.

But the genetic homogenization on a genome-wide inter-population scale mediated by migration does necessarily hold for culture. It may in some cases, but by and large it does not. This is most easy to illustrate with language, and that is why I focus on that example. The case of the “rape of the Sabine women” by the early Romans is a legendary illustration of the distinction between cultural and genetic inheritance. The Romans assimilated many groups early in their history. In fact, the elite patrician gens Claudia even had paternal Sabine ancestry. But no matter the biological nature of their genealogy the Latin Roman cultural matrix persisted, and propagated. The children of the Sabine women were culturally Roman, not a hybrid between the Sabine and the Roman.

One can illustrate this reality with other cultural characters. Modern Mexicans are a genetically hybrid population between Europeans and Amerindians. But their religion is a European sect (even if their Roman Catholicism has an indigenous flavor, no one would confuse it with the Aztec or Maya religion). Their language is also a European language (even if there are indigenous loan words, regional Mexican Spanish is intelligible with Castilian). But, their cuisine arguably has a predominantly Amerindian basis, albeit inflected with Iberian influences.

The focus on regional, ethnic, and national constructs here is not coincidental. Cultural variation as noted above exhibits high levels of inter-group variation. When comparing the genes of the Yoruba and Tuscans, most of the variation is within each group. But when comparing the language of the Yoruba and Tuscans, most of the variation is across the two groups. The organismic analogy for groups or cohorts of individuals applies much more appropriately to cultural entities than it does to biological genetic abstractions (e.g., the Body of Christ). The origin of the term shibboleth illustrates the functional relevance of this reality of inter-group variation: even though culture is highly plastic across generations and populations, it is not always facultative in the lives of individuals. The way you speak marks your origins and your class. It constraints your norms, and shapes with whom you identify.

And with that, back to my daughter. She will speak English, and she will be irreligious. Her norms and views will not be atypical for the average American. She will eat bacon (OK, she has), and when of age, drink beer. In all ways culturally that matter she resembles her maternal grandparents, and not her paternal grandparents. There was never a great question about this. In choosing to bring up their children to an American milieu my parents risked severing us from the culture in which they were embedded, and which nurtured them. So it is, and so it will always be. The dreams of generations past may die, but their genes live on.

* Her whole recent pedigree has been genotyped, so these proportions are known with precision.


Comments (11)

  1. Dan_ny

    It’s probably not very fruitful to look at cultural inheritance at the individual level. After all, quite often the four (unrelated) grandparents who come from the same generation and lived through the same events, (maybe) listened to the same music, used the same technologies, will have more in common with each other than with their grandchildren (to whom each of them is related genetically) who move in a different cultural milieu and will absorb different influences, more from society at large than from their parents and grandparents.

  2. An interesting conclusion one might draw is if there are strong differences between populations on a given mental trait,it is likely those are a result of socialization rather than genetic differences. Further, the likelihood of these traits being cultural rather than genetic becomes greater the closer the two populations are geographically. Presuming, of course, a given trait is neither heavily selected for or against in either population. Indeed, this seems the case for cross-cultural differences in the “big five” personality traits.

    Whether it extends to other domains remains to be seen I suppose. “Big data” should be able to quickly show us if things like IQ have sharp boundaries (suggesting culture is the root between variance), or fuzzy boundaries (suggesting genes play a major role).

    • ohwilleke

      What a fascinating methodology to tease out nuture v. nature distinctions and to quantify gene x environment relationships. Also interesting is that the methodology will generally show relevative nuture v. nature contributons as a percentage or ratio, rather than simply assigning a trait to one or the other.

  3. Paul Givargidze

    Thanks for the piece. Just a note regarding something stated on Wikipedia. It may not be of any particular significance to your article, so I hope you do not mind the comment.The term “shibboleth” may not be Hebrew in origin, as stated in the Wikipedia article. It may be Akkadian. In addition to the meaning “ear of grain” in Akkadian, in the Standard Babylonian variety of Akkadian it was another term for the constellation Virgo.

  4. marcel proust

    And with that, back to my daughter. She will speak English, and she will her parents will raise her to be irreligious.


  5. Razib, is there a way to get the larger version of the bottom map? When I click on it it doesn’t get bigger and I’d really like to read it.

  6. ohwilleke

    It is also worth considering that different domains of cultural inheritance have different transmission and survival properties.

    For example, it takes much more powerful and particularized conditions to effect language shift than it does to effect a change in religious affiliation. Almost no one changes their “native” language or makes major adjustments to their phoneme set as an adult, even if adults learn new languages, but many people undergo religious conversions as adults.
    Despite (or perhaps because of) the ease of transmission, folk tales and folk religion often persist long after language shift and organized religion have obliterated many other residual traces of prior cultures.
    Part of the chunky v. creamy distinction arises from the powerful impact of social status inequalities on cultural transmission. Historical, children learn the language of their at that time higher social status fathers. Ordinary people emulate elites but not visa versa for the most part. People adopt languages that are associated success in an area and shed languages when they feel that their own fellow language speakers are socio-economically or culturally inferior. This hierarchical pattern of cultural transmission homogenizes the culture of everyone within the scope of influence of any given elite group, and the bigger coherently organized societies get, the bigger the chunks become. The culture of Paleolithic peoples may have had considerable smaller chunks than we do today.

    “Language, religion, and culinary preferences are accidents contingent upon one’s parents’ preferences.”

    Yes, mostly and partially. Culinary taboos are cultural, but culinary preferences have a significant genetic component. Lactose intolerance is the most famouos case, but there is material genetic diversity in how one’s taste buds process different taste – for example, some people have hypersensitive “bitter” tastebuds and often develop an aversion of raw vegetables with some bitterness in them as a result. Other people find that olive oil in large quantities doesn’t agree with them.

    Likewise, while the content of the religious beliefs that a person holds is transmitted culturally the propensity of a person to show religiousity may well have a substantial genetic component.

    Also saying “parental preferences” drive what is culturally transmitted to children really isn’t even very close to right (“parental choices” would be more accurate). Parents in immigrant families routinely and indeed, almost invariably, intensely want to instill elements of their birth culture in their native born or young migrant children, and they almost always mostly fail in the attempt. The only places where the failure rates isn’t so intense are immigrant communities that have sufficient critical mass and insularity that the entire village that raises a child shares the cultural features that the parents want to transmit, not just the parents. Assimilation is virtually inevitable in the absence of ethnic ghettos.

    Parsing nuture v. nature on some behavioral traits generally viewed as cultural (e.g. culture of honor style aggression-incitation responses) is often hard because even if you do find a gene correlated to a cultural trait, it could simply be an unrelated ancestry informative trait for a disproportionate share of people in that culture.

  7. I’d love to see you try to apply the same methodology and reasoning on Malaysia’s multicultural.

  8. raviy101

    This actually answers a long standing question of mine. Why people who remarkably are similar( ex: people in South India ) kill each other over caste differences.

  9. razibkhan

    I think this is misleading if it suggests that culture and language are much the same thing

    it doesn’t, so it’s not misleading. though i suppose that stupid people might infer that language == culture


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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 http://www.razib.com


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