A few people have pointed me to Charles Murray’s comment at The Enterprise Blog, The Debate about Heritability of General Intelligence Radically Narrows, which alludes to the recent finding of genomic confirmation of the behavior genetic heritability measure for intelligence. Murray indicates that this should end the “debate” on the heritability of intelligence as a quantitative trait. As I implied earlier much of this debate had more to do with rhetoric and ideology than reality, in that I doubt many people support a very low heritability measure for intelligence ( < ~0.30) in developed societies when they don’t have strong ideological commitments. These commitments being that social policy can homogenize environments enough that only the genetic components of variation of a trait value will be important in the future, so that heritability values will go from ~0 to ~1.0.
At this point some of you may be rather confused. What I’m saying here is that the logical end point of a quasi-”blank slate” policy position is the diminution of environmental impacts so that only genes matter. For a complex trait like intelligence this final state of ~100% of the variation being due to genes is probably not possible. Variation in height for example is indubitably biologically specified, but even in developed nations where there is a surfeit of nutrition only ~90% of the population level variation is due to variation in genes. That means that ~10% of the variation remains “environmental,” which is a catchall category and may include biological dynamics such as gene-gene interactions or developmental stochasticity. But the 90% figure for height is recent. In the 19th century a considerable proportion of the variation in height corresponded with variation in class. The upper classes ate well, and the lower classes did not. But this truism varied by locale. For example:
Income was protective of nutritional status as one would expect. The height of the upper class in America did not decline in the mid-19th century. In fact, the difference in height of upper class men and the average increased from 1 cm to 3 cm between 1830 and 1840. This was much less than the social differences in Europe. The greatest social gradient in height ever recorded was found in early industrial England, where the difference between the upper and lower class 15-year-olds reached 20 cm….
The following figure is likely to shock, and highlight the different median ecological conditions on the two sides of the Atlantic:
Observe that in the 19th century American slaves were taller than the English lower class! That’s a testament to the fact that America was in a state of incredible land surplus and labor shortage, which high per unit agricultural productivity. Even the slaves prospered (the slaves in the United States of America had above replacement fertility, which was exceptional among New World black slave populations). In other words, the environmental variation (nutrition) was less of a factor in determining height in the New World than the Old, so heritability of height was far higher in the New World than the Old. Of course because class exhibits heritability in the colloquial non-genetic sense in the Old World height was a strong tell as to one’s position in the status hierarchy. Far less so in the New World, where genetic endowment loomed larger. Likely the range of height decreased in the New World, as the very small malnourished individuals were not present within the population, but of the variation which remained a much larger proportion was explained by genes than had previously been the case. This still stands in some very poor nations today, where the heritability of height is lower than in the developed world.
If it turns out that the heritability of intelligence is relatively high in the developed world, then it may be that the Left-progressive project of ameliorating class based differences in access to cognitively enhancing environments has succeeded to a large extent. Barring genetic engineering this is the “end of history” for this project. It is a matter of when, not if (i.e., if you reject that the project has hit sharply diminishing marginal returns, logically it should at some point if the Left-progressive project succeeds). Assortative mating and more transparent meritocracy should allow for cleaner sorting within the population, and inter-generational class churn should decrease and stabilize at a basal level dictated by the random environmental variables which no amount of social engineering can squeeze out of the system. A perfect meritocracy would replace cultural class with biological caste.
Razib Khan’s degrees are in biochemistry and biology. He has blogged about genetics since 2002, previously worked in software development, is an Unz Foundation Junior Fellow and lives in the western US. He loves habaneros.
August 15th, 2011 at 11:49 pm
Even with assortive mating rates held constant, since reducing environmental causes of intelligence variation would increase genetic variation, would we expect a long-run increase in the standard deviation of intelligence?
More practically – reducing environmental causes of intelligence variation would tend to reduce generational social mobility, so long as socio-economic status correlates to intelligence. Is this happening already? Could this explain the lower generational social mobility in the U.S. as compared to Europe?
August 16th, 2011 at 12:22 am
Even with assortive mating rates held constant, since reducing environmental causes of intelligence variation would increase genetic variation, would we expect a long-run increase in the standard deviation of intelligence?
i don’t think so. reducing the environmental proportion increases the genetic proportion, it doesn’t increase the genetic variation. IOW, the absolute quantity of genetic variation is held constant, but it’s relative weight increases. if you had large variations in iodine consumption you’d have larger phenotypic variance through cretinism, not less.
August 16th, 2011 at 1:31 am
What’s the source for the data in the height graph?
August 16th, 2011 at 8:14 am
Human mental abilities are complex and should be ranked on many dimensions. Then we can have a discussion of intelligence.
August 16th, 2011 at 10:27 am
What’s the source for the data in the height graph?
it’s the book i linked. i don’t provide links as aesthetic sugar, fyi.
Human mental abilities are complex and should be ranked on many dimensions. Then we can have a discussion of intelligence.
ok, i’ll shut up then. you know best.
August 16th, 2011 at 11:50 am
Provocative thought, and I think perfectly true as stated: “A perfect meritocracy would replace cultural class with biological caste.” But even though the US is relatively meritocratic, we are far enough from a “perfect meritocracy” to be in no danger of becoming stratified by biological caste…In most parts of the country, a truly exceptional child does have a good chance of getting ahead (we are talking really exceptional, and even then, shit happens). But for most people, chances are that you stay in the class into which you were born. I am sure everyone who has worked in the inner cities can testify to the fact that MANY apparently bright children get derailed in their later teens…thats culture, not genes. Conversely, many dumb rich kids in connecticut go on to have a very comfortable life. Inherited privilege exists, even in these United States.
Whatever one may think of the desirability of such a project, we are not there yet.
August 16th, 2011 at 2:29 pm
“As I implied earlier much of this debate had more to do with rhetoric and ideology than reality, in that I doubt many people support a very low heritability measure for intelligence ( < ~0.30) in developed societies when they don’t have strong ideological commitments."
Many people were arguing (a la Flynn) that the high heritability figures were illusionary, an artifact of the kinship methodology and a product of gene-environment correlations, etc.
In that sense they were not arguing that heritability estimates were low, just misinterpreted.Just a half of a year ago in "When genes matter for intelligence?" you stated "In other words, your genetic disposition can shape the environment you select, which can then serve to express your genetic potential in a specific manner," and highlighted the importance of both GXE interactions and GE correlations in producing IQ differences. Scott Kaufman made a similar case in an article over at Huffpost. The significance of this study is that it largely vindicates kinship findings of a large additive genetic component and puts a ceiling on the magnitude of variance that GXE and rGE could possibly explain. In that way, it, to use Murray's phrase, radically narrows the debate.
August 16th, 2011 at 2:39 pm
It is notable that personality traits like extraversion and conscientiousness have the same distribution in very high IQ people that they do in the general population, and yet are very material to the earning potential in that populatioon (this is a late stage finding of the Tremain study which Hsu cited at Information Processing earlier this year). This implies that baseline stability in personality tratits that are material to socio-economic success (and are probably far less polygenetic than IQ) is much lower than baseline stability in IQ.
It is also notable that while IQ and personality traits continue to have marginal value all the way up to the top of the distribution, that even the people highest in all personal traits (IQ and personality) that were predictive of high income and wealth, weren’t anything more than middlingly upper middle class in their economic success. Certainly, the folks in the top 99.5% by these personality and IQ measures weren’t anywhere near the top 99.5% by economic success measures. Put another way, everybody who is at the very top economically is fortunate and vastly overachieving relative to their birthright endowmen of ability.
IQ and the like may be necessary, or at least, very helpful at taking advantage of an opportunity to become truly rich, but it takes inherited wealth or great luck at finding an opportunity to break the upper middle class glass ceiling.
It is also worth pondering how strong assortive marriage would stay in an equal opportunity society. One of the reasons for assortive marriage is to give your kids a fair shot in life. Marry well and your kids will be able to enjoy their full potential. It isn’t obvious that this imperative would be as great in an equal opportunity society where everyone reaches their full biological potential.
If assortive marriage norms fell apart (and they are at a high water mark right now), then the biological caste notion disintegrates with it.
August 16th, 2011 at 3:24 pm
Let’s talk about Germans, not the English, because there is more data. Would the graph look very different for their descendents? In the end the slaves were slightly taller, and that has reversed today, but most of the gap at age 15 was due not to final height, but to speed of maturation. I believe that in America today blacks mature faster than whites.
Of course, the class part of the graph shows that maturation then was largely environmental.
(I assume that the graph is just males. If I recall correctly, in America, black men are almost as tall as white men, but black women are somewhat shorter than white women. If this graph is both sexes, then the change of the difference of final heights is large.)
August 16th, 2011 at 4:39 pm
I am sure everyone who has worked in the inner cities can testify to the fact that MANY apparently bright children get derailed in their later teens…thats culture, not genes.
Maybe it is indeed a poor environment (e.g., ghetto culture) in the end overwhelming a genetic predisposition to be smart. Or it could be the opposite – a genetic predisposition to be not so smart finally overwhelming an early environmental intervention (from those very people “working in the inner cities”, HeadStart, etc.).
August 17th, 2011 at 2:49 am
The fundamental fallacy of this otherwise great post is the assumption that the English classes come from the same genetic stock. Obviously there is much more Norman DNA in the upper classes and more Anglo-Saxon in the lower classes. Also, what’s the point in comparing with American slaves? It’s all genetic!
August 17th, 2011 at 10:16 am
Ziel, I assure you, that is not the case. These are really smart kids, doing well at school, then they get to be teenagers and the culture is gangs and drugs and it all falls apart…or the schools are so bad, the above average ones also fall behind the national average (peer pressure, community norms and so on)…I am not making a case for head start (which may do less than advertised anyway) or any other “leftie” intervention, just saying that there are definitely above average youngsters in poor neighorhoods (not claiming their proportion is exactly the same, I dont know if it is or is not) and their chances of success in life are nowhere close to exactly equal IQ children in a “good” neighborhood. This is not meant to be an argument for socialism or whatever may or may not bother you about society, just an empirical observation that there is a vast gulf between outcomes in the middle class and outcomes in the poorer neighborhoods and its not just genes….a lot of it is culture. What can fix the culture and what makes it worse are entirely separate arguments.
August 17th, 2011 at 10:46 am
I don’t think this is a radical insight. Every social worker can point you to problem families who have been at the bottom of the ladder for generations because of their low IQ and/or tendencies toward substance abuse and aggression.
Of course society in most Western countries has become less meritocratic in the last decennia instead of more (probably with the exception of some Scandinavian countries and Finland), so the ‘end of history’ for this project is probably still centuries away.
And I wonder how much physical attractiveness matters as a counterweight to assortative mating of people with similar IQ.
August 17th, 2011 at 8:56 pm
Omar,
Not that I do not trust you assurances, but do you know of a study that shows your point?
August 18th, 2011 at 2:53 pm
Hi Razib. I find disturbing all this talk of assortative mating and biological castes, as it sounds eerily similar to eugenics. Please correct me if I’m mistaken to be making this connection.