Gene Expression

The t-shirts which depict the “ascent of man” from hairy semi-ape to upright Homo sapiens might make you think that human evolution has been trivial since the emergence of our own species. Modern genomics suggests this isn’t so, selection coefficients on the order of 1-10% are probably rather normal, and iterated over hundreds of generations that could result in a nontrivial amount of change on a quantitative trait.

I bring this up because a few days ago in The New York Times a piece was published titled The Twists and Turns of History, and of DNA. Greg Cochran (interest divulgence, a friend of mine) offered the boldest quote:

“Since it looks like there has been significant evolutionary change over historical time, we’re going to have to rewrite every history book ever written,” said Gregory Cochran, a population geneticist at the University of Utah. “The distribution of genes influencing relevant psychological traits must have been different in Rome than it is today,” he added. “The past is not just another country but an entirely different kind of people.”

This is explosive stuff, but it shouldn’t surprise anyone coming from Greg. Earlier this year his “dangerous idea” in response to John Brockman’s question was an elaboration on this concept: the past is undiscovered territory. In their recent book Not by Genes Alone quantitative anthropologists Peter Richerson and Robert Boyd start out with the assumption that it is simply implausible that differences in allele frequences across populations could explain any of the variation in culture we see around us. Richerson and Boyd’s model utilizes population genetic models in a “memetic” context, and appeals to the peculiar character of ideas to put forward an argument for cultural group selection because of the possibility of high intergroup variance in traits. Greg’s ideas would throw another complexifying parameter, gene-culture coevolution. But Richerson and Boyd’s point is well taken insofar as the quicksilver changes in cultural biases are unlikely to have long term genetic implications, rather, the idea that society has a shaping influence on the nature of selection must be drawn from a subset of extremely salient and persistent changes that would drive long term fitness differentials.

What could be a candidate for a cultural-social change would should shift allele frequencies? Consider agriculture. In much of Eurasia, in particular northern Europe, the Neolithic revolution clearly shifted allele frequencies as the capacity for adult lactose digestion became normal, a derived condition. In contrast, societies where cattle husbandry never took root did not exhibit any change from the ancestral genotype (ergo, phenotype). There are non-European societies where adult lactose digestion is normal, in much of northern India for example milk is an important part of the local cuisine, often in the form of a butter (ghee). In contrast adult lactose digestion is less common in southern India, where coconut oil plays a larger role (and the climate is likely less salubrious for cattle). In Africa there are Nilotic cultures which have independently evolved toward the lactose tolerant phenotype, but those agriculturalists who reside within the tsetse fly zone where cattle can not flourish remain in the ancestral condition. The point is that selection can operate over time and space in interaction with cultural innovations, which themselves might be constrained by environment or contingent upon historical vissitudes.

One can see this in our very forms over the last 10,000. Humans have become more gracile during the transition to the settled Neolithic life. Our skulls are smaller and our dentition more delicate. This is a common tendency of all agricultural peoples, as an underlying selection parameter seems to be operative as populations transition toward agriculture away from the hunter-gatherer lifestyle. Our faces seem to be shrinking by at least 1-2% every 1,000 year. There is even evidence that great changes in the size of human faces have transpired over the past 1,000 years.

The lesson is that time does not stand still, and we are not outside of nature. And if this is the trajectory toward which gracility drives us, well, I’m not complaining! i-d24656110eb4cad0bed8bf8fd8d06d90-Jessica_Alba_192071g.jpg

Comments

  1. #1 John Emerson
    March 13, 2006

    Just let me put in my recurrent plug for institutional influences. These are a sub-category of cultural influences, which I stress because for many “culture” means subjective, esthetic, personal, local types of things. Institutional differences, by contrast, are public, objective, and weighty — law, authority, property rights, etc.

    For example, Dutch are significantly different than Germans only institutionally, not racially or linguistically. But 300+ years of different institutions make an enormous difference.

    It is my belief, for example, that “individualism” as a character type is a product of legal individualism, which requires the destruction of clans and other such collectivities. Once people are allowed to be individualistic (once collectivities are no longer able to enforce their rules) they will be.

  2. #2 razib
    March 13, 2006

    It is my belief, for example, that “individualism” as a character type is a product of legal individualism, which requires the destruction of clans and other such collectivities. Once people are allowed to be individualistic (once collectivities are no longer able to enforce their rules) they will be.

    i don’t think any one thing would be able to explain the whole extent of variation. in geography of thought nisbett points out that ‘individualism’ tends to peak in northern europe, in particular anglophone countries, and be rather low through most of the world with a mid-point in continental europe. is continental europe equidistant because of genetic factors vis-a-vis england/scandinavia and the rest of the world? no, continental europe is very close to england/scandinavia in terms of genetics, so obviously cultural factors are important. similarly, asian amerians tend to be either equidistant or more like other americans, re: individualism in the context of the east asian-american spectrum. nisbett’s book also reports research that people in hong kong are adept at ‘switching’ cognitive styles.

    this suggests a high degree of plasticity. that being said, work like jerome kagan’s does suggest that certain behavioral biases do exhibit intergroup differences from an extremely young age (blonde and east asian introversion vs. controlled samples of white infants for example). would this have an impact on culture? i think so, though i’m not sure that we could easy construct a linear prediction equation…because cultural systems are not linear and like possess many confounding parameters. this is why i’m saying that greg’s ideas are a complexifying wrench thrown into the models, they don’t make everything “simple” and clear as day (though some stupid people do to genes what they do to culture, use it as a total explanatory model). it adds another layer that needs to be taken into account to get through the fog.

    on many cultural tendencies we see some sort of trend the explanatory parameters are probably all going to be historical/social. that being said, if east asians are “naturally” more introverted than papuans, that might come into play in the types of cultures they produce….

  3. #3 TangoMan
    March 13, 2006

    In Africa there are Nilotic cultures which have independently evolved toward the lactose tolerant phenotype

    Bloom and Sherman compiled data on 270 indigenous African and Eurasian populations in 39 countries and found 13 lactose-tolerant populations that live side-by-side with lactose-intolerant populations. The likely distinction is nomadism and the populations were fairly discrete despite proximity.

  4. #4 jaimito
    March 14, 2006

    The idea that people changed in historical times is well known and elaborated in supremacist historiography. It seems obvious to any observer that contemporary Greeks have little or nothing in common with the Athenians of Plato´s time. But the cause of the change is mixing more than evolution. And malaria.

    Gene frequencies must have changed most dramatically in last 200 years in Europe. How many of the children of a first grade class in France are descendants of the soldiers of Napoleon?

  5. #5 John Emerson
    March 14, 2006

    Razib, one of my points was that individualism is possible only within individualist institutions. This is a bit different than a “causal” statement. It’s sort of like saying that bicycle-riding requires bicycles. An individual can’t be an individual on his own; he needs an environment which accepts individualism, or an “individualist culture”.

    In most traditional societies a large number of institutions work to minimize individualism, using control of resources and rewards and ultimately force to enforce deference. There are attempts at resistance and escape, but they are repressed.

    Put people from those societies in a different social-legal-political system, and they’ll behave differently and develop different personality types.

    Comparisons of Taiwan Chinese with their American grandchildren or cousins would bear me out, I think. Even though Chinese-Americans are less individualist than many other Americans, they’re more individualist than Taiwan Chinese. (Furthermore, the American example has transformed Taiwan institutions too; a better example would be a mainland Chinese village with cousins in the US.)

    Changes in sexual behavior in Spain between 1960 or so and the present would be another example. The prudishness and protective paternalism toward girls of traditional Spain existed because it was enforced by both the Chursh (which had power) and the State. The Church has much less power and the State is less involved in prudishness, and from what I’ve told the sex bomb has exploded there in a big way. Swedes have been sexually free for a long time, but they’re sort of careful, sensible people compared to the Spaniards.

  6. #6 Oran Kelley
    March 14, 2006

    “Since it looks like there has been significant evolutionary change over historical time, we’re going to have to rewrite every history book ever written,” said Gregory Cochran, a population geneticist at the University of Utah. “The distribution of genes influencing relevant psychological traits must have been different in Rome than it is today,” he added. “The past is not just another country but an entirely different kind of people.”

    Except that the reason why we say the past is “another country” is that we assume that the cultural differences across the ages are quite considerable and that we will be wrong if we assume Romans, say, are just like us. In fact they may be surprisingly different. Thus, the expression.

    So we already realize there are big differences between ourselves and , who cares whether they are on account of culture or on account of genetic changes (about which we know no historically significant particulars–they may turn out not to matter very much) or both? How does that actually make a difference for an actual historian?

    Right now, I’d feel pretty safe in saying no history will have to be rewritten. It’s satements like these that make me wonder whether some folks consider themselves promarily to be salesmen for their fields of study or seekers of truth. And here again, I have to note how similar the rhetoric–everything is a revolution, nothing will ever be the same again (and all before any real findings are in)–is to what we heard in the heyday of postmodernism.

    Does get one in the newspaper, though.

  7. #7 gcochran
    March 14, 2006

    I said it because that’s what I think. Look, man, if a new version of a gene controlling myelination can go from one individual 6500 years ago to over 50% today – and it has, neuregulin – and if there are _many_ genes undergoing such sweeps, which there are – there are likely going to be real differences in human inclinations and capabilities over time. Biology keeps culture on a leash. It may be a short leash.

  8. #8 razib
    March 14, 2006

    who cares whether they are on account of culture or on account of genetic changes (about which we know no historically significant particulars–they may turn out not to matter very much) or both

    oran, your modus seems to be one of profound skepticism at everything which is not coterminus with the bounds of your own knowledge. skepticism is a necessary feature of human cognition and proper analysis, but i wonder, what do you believe in a positive sense? i know what you don’t care about and find implausible.

  9. #9 Oran Kelley
    March 14, 2006

    I believe skepticism is a mighty fine thing ;-)

    I believe my skepticism is a long way from being radical.

    I believe a lot of sorta-scientific proclamations I read can do with a greater exposure to skepticism.

    I believe scientists sometimes make grand proclamations about history writing or literature without knowing very much about those subjects.

    I believe scientists speaking on these subjects in fora like the New York Times need to be a lot more rigorous in distinguishing what they know to be true from what they wish to be true, and to studiously avoid being quoted as experts when they express the latter.

  10. #10 John Emerson
    March 14, 2006

    While I see it as my role here to advocate for institutional causes, for the record I should say that I do not think at this point that recent genetic change can be ruled out as inconsequential.

  11. #11 ManhattanTransfer
    March 14, 2006

    Oran,

    You ask “who cares?” Well, I do. I want to know about the truth of these things. Mostly, I want to know because the truth is interesting. I may not be an “actual historian” but the role of genetic change in history matters to me. So I’m glad people are doing this work.

    Best,

    MT

  12. #12 Dan Dare
    March 15, 2006

    No doubt you are all aware that the standard unit of female beauty is the millihelen – Defined as the amount of beauty required to launch 1 ship.

    So Jessica is beautiful alright. But has she launched any ships?

    By the way ugliness is measured in negative millihelens, defined as the amount of ugliness required to sink 1 ship.

  13. #13 PJGoober
    March 15, 2006

    lol

  14. #14 Orna Kelley
    March 15, 2006

    While I see it as my role here to advocate for institutional causes, for the record I should say that I do not think at this point that recent genetic change can be ruled out as inconsequential.

    But can we assume they are consequential enough to predict a wholesale rewrite of history?

  15. #15 oran kelley
    March 15, 2006

    You ask “who cares?” Well, I do. I want to know about the truth of these things. Mostly, I want to know because the truth is interesting. I may not be an “actual historian” but the role of genetic change in history matters to me. So I’m glad people are doing this work.

    I’m glad they’re doing the work, too. What I question is the rush to judgement in the interpretations here. All we know so far is that there are some genetic differences between us and folks who lived in the medium (rather than long)range past. That’s it.

    We don’t know how big these differences are, and we don’t know what effect they may have had on the people who made and experienced history. So from a historian’s perspective I don’t see how what we know is worth worrying about. Especially considering the fact that a lot of historical work over the last 25 years, influenced by the much maligned Clifford Geertz, has been written as if people in the past were ontologically different from us anyway. (There’s some irony for you)

    I’m not against gathering knowledge. I’m against grand specualtion and public chest beating based on very small preliminary bits of actual knowledge.

  16. #16 John Emerson
    March 15, 2006

    “Rewriting history” isn’t an unusual event. It’s one of the historian’s main jobs. Historians frequently redo someone else’s work, better.

    So yes, if there’s enough substance in these genetic theories, history will be rewritten. I tend to be a skeptic about this, but I also tend to think that continuity and conservation are too often assumed.

  17. #17 Oran Kelley
    March 15, 2006

    “Rewriting history” isn’t an unusual event. It’s one of the historian’s main jobs. Historians frequently redo someone else’s work, better.

    Yes, or there wouldn’t be too much for historians to do. But, “we’re going to have to rewrite every history book ever written” sounds a bit more dramatic than “history will pretty much carry on as it always has, rewriting itself.”

    continuity and conservation are too often assumed

    Yes, and no. 9/11, the Internet craze, post-humanism . . . there are definitely recent examples that make me think there’s a certain fashion for outrageous overstatement, too.

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  19. #19 cat deeley
    June 13, 2006