Adaptive Complexity takes issue at a post over at Information Processing over race & genetics. On that specific topic, let me just quote Luigi Luca Cavalli-Sforza:
[my question] Question #3 hinted at the powerful social impact your work has had in reshaping how we view the natural history of our species. One of the most contentious issues of the 20th, and no doubt of the unfolding 21st century, is that of race. In 1972 Richard Lewontin offered his famous observation that 85% of the variation across human populations was within populations and 15% was between them. Regardless of whether this level of substructure is of note of not, your own work on migrations, admixtures and waves of advance depicts patterns of demographic and genetic interconnectedness, and so refutes typological conceptions of race. Nevertheless, recently A.W.F. Edwards, a fellow student of R.A. Fisher, has argued that Richard Lewontin's argument neglects the importance of differences of correlation structure across the genome between populations and focuses on variance only across a single locus. Edwards' argument about the informativeness of correlation structure, and therefore the statistical salience of between-population differences, was echoed by Richard Dawkins in his most recent book. Considering the social import of the question of interpopulational differences as well as the esoteric nature of the mathematical arguments, what do you believe the "take home" message of this should be for the general public?[Answer] Edwards and Lewontin are both right. Lewontin said that the between populations fraction of variance is very small in humans, and this is true, as it should be on the basis of present knowledge from archeology and genetics alike, that the human species is very young. It has in fact been shown later that it is one of the smallest among mammals. Lewontin probably hoped, for political reasons, that it is TRIVIALLY small, and he has never shown to my knowledge any interest for evolutionary trees, at least of humans, so he did not care about their reconstruction. In essence, Edwards has objected that it is NOT trivially small, because it is enough for reconstructing the tree of human evolution, as we did, and he is obviously right.
But that's not what I want to talk about. Michael at Adaptive Complexity says:
Complicated traits, involving many genes with likely pleiotropic effects are, given human population history, much less likely to differ significantly (at least the genetic component) between different populations.
Quantitative polygenic phenotypes such as intelligence and height would be "Complicated traits, involving many genes with likely pleiotropic effects." Earlier he says:
there has been a fairly substantial amount of gene flow among human populations over the last 50k years, which tends to act against population differentiation. Given what we know about human population history, and the likelihood that a very complex trait like intelligence is controlled by many genes with pleiotropic effects, I find it implausible that significant differences in intelligence between populations have arisen over the past 50k years.
I need to open my quantitative genetics textbooks again perhaps, but I'm a little confused by this. We already have a great deal of extant variation on quantitative traits like intelligence and height. In other words, there's a lot of variation out there that doesn't seem to have deleterious consequences for selection to work from. I don't get why 50,000 years just isn't long enough for natural selection to shift the distribution of phenotypes when we already have a great deal of heritable variation across our species. The rate of phenotypic change is rather simple for a quantitative trait; it is proportional to heritability (which is a nice proxy for the correlation between the phenotype and genotype on the population level) and strength of selection. Because this process is reducible the same can be said of traits dominated by genes of large effect, though here we would would probably substitute the term penetrance for heritability.
What am I missing? (a citation to a page of Mike Lynch's Genetics and Analysis of Quantitative Traits would be nice)
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If we can get the variation in height at population level evident between, say, Germans and Filinos, why not intelligence?
Fortunately, unlike Zeeb, I don't have to be nice to people who wear their ignorance like a badge of honor:
"it is naive to think that the selective pressures on human populations are anywhere close to the highly engineered selective pressures you find in animal breeding"
Thank goodness we have some really naive geneticists out there, then. Is it too much to ask for a "scientific" blogger to pull his head out of his ass and read the literature before he makes a sweeping claim? We have multiple verified examples of alleles going from nil to ubiquity in a few hundred generations -- divide by about 10 to convert to dog generation times and the rates of change look like they'd be pretty comparable.
It's trivially true that the effectiveness of selection is limited (all else equal) by the amount of pleiotropy. What vexes me is that people who point this out don't draw the logical conclusion from this fact that selection will tend to disfavor architectures that involve a lot of pleiotropic interactions (all else equal). That's why most genetic variation is additive. At the risk of encroaching on someone else's schtick, this is "obvious, obvious, obvious".
This is N. Chomsky's old argument. Given that it is already known that intelligence has no demonstrable population-level genetic inheritance that matters (regional/population differences in measures of intelligence go away with the baby swapping test or are clearly otherwise tied to social/environmental factors) it seems no longer necessary to make this political argument even if you wanted to. In any event, it is too similar to Paley's Blind Watchmaker for me.
Now, for height, that is a different story. In my view most interpopulation differences in height are not easily explained by genetics but some are. The "complex" model for height is a mistake, I am guessing, where non-genetic factors are confounding things and people who must have height be genetic (always) simply swap to the complexity argument. Where we know height variaiton is genetic it isn't so complicated.
"it is already known that intelligence has no demonstrable population-level genetic inheritance that matters"
It's amazing how many things are known that aren't so. In order to justify that statement according to anything resembling modern standards of scientific rigor, you'd have to, say, do a well-constructed admixture mapping study with IQ as the phenotype and have it come up with a null result. That would be pretty much the gold standard and ought to end the argument. Let me know if you hear of anyone planning such a thing -- and if you're a gambling man we can bet on the result.
do a well-constructed admixture mapping study with IQ as the phenotype and have it come up with a null result.
How convenient to suggest an experiment that can't be done. Experiments that can't be done are often the gold standard, yet science seems to move ahead anyway, somehow.
But natural versions of this experiment have been done, including on in Briton in which children of "black" vs. "white" vs "mixed" 'race' were raised together from infant age in an orphanage, with special training to not treat them in the usual race biased ways, and then they were given various IQ tests. There are other natural experiments as well, but that is the coolest one.
There have also been studies measuring effects on intelligent that generally erase race as a factor, showing instead that SES and so on are. These studies have mostly driven racist idealogs off of the US and European based data because the data no longer supports their cause. The latest montra is taking various intelligence measures between nations and using that to show the apparently preconceived results.
Anyway, getting back to the British orphanage case: Of all the results of the tests, only one pair of numbers is statistically (barely) significant in difference, and that happens to be NOT a white smarter than black result as many who have bought into the politically motivated anti-science racist rhetoric would expect. I think its black that stands out over white or mixed (can't remember off hand)
We need to ask Greg (Laden) to give us those references. Preparing for a class last year I asked a prominent IQ nay-sayer for references to studies showing effects of early childhood environment on IQ. He sent a few references, and the studies were so bad that our seminar disbanded early that day because there was nothing to talk about.
There are indications that childhood IQ is malleable but environmental effects that people have followed do not persist, i.e. heritability goes up with age until around adolescence.
Henry
How convenient to suggest an experiment that can't be done
why can't that experiment be done?
You're not going to like this ,Henry, but I think you can find references to both studies I mention in Dick Lewonton's "Human Variation" textbook.
One problem with heritability generally (and in this case especially) is that we know that in all measures, all studies, everywhere ever basic school related performance is linked to SES, home environment, and parent's educational level. Therefore, yes, people inherit this stuff, but then two generations in a row go to college, get good jobs, move out of the lead-poisoned self esteem destroying ghetto and the school system where number one concern on a day to day basis is violence and not learning, and guess what. Performance changes.
And some things people believe because they are obvious, just are not so. The Japanese believe they are a 'small' race. And they always have historically been much shorter than their neighbors and various foreigners they compare themselves with. But when I taught high school in Japan even some of the young girls were approaching my 6' height. Young adult males still average shorter than me, but plenty are as tall or taller.
It apparently takes more than one generation for good nutrition to have its effects. I predict that in another generation the Japanese will average just as tall as other well-fed races.
Things we think now are genetic may well turn out not to be. The tail ends of height and intelligence distributions may have a lot to do with fairly subtle nutritional differences, or have other causes, along with genetic components.
There are other natural experiments as well, but that is the coolest one.
You never hear about the follow-ups to the Tizard study (which tested four year olds). There is a good reason for this.
The transracial adoption literature certainly doesn't support you, Greg.
"One problem with heritability generally (and in this case especially) is that we know that in all measures, all studies, everywhere ever basic school related performance is linked to SES, home environment, and parent's educational level."
Except in every adoption study the correlation between the adoptive parents and their non-genetic children is something close to, if not exactly zero:
See here for adult income.
There have also been studies measuring effects on intelligent that generally erase race as a factor, showing instead that SES and so on are.
No there haven't. This is a myth. The race differences get larger at higher levels of income. Whites from households in the lowest income bracket have higher IQ scores than blacks from households in the highest income bracket:
Given what we know about human population history, and the likelihood that a very complex trait like intelligence is controlled by many genes with pleiotropic effects, I find it implausible that significant differences in intelligence between populations have arisen over the past 50k years.
i've pulled out the most immediate elements of dissonance to my estimation.
the "complexity" of intelligence is not a product of a demonstrably intricate map out-bound from the genotype. intelligence is complex in that it is a trait at which the explanatory value of genotype and phenotype as concepts crumbles i.e. intelligence is a complex case for theory. an element of intelligence that stymies theory is that it is cryptic, by which i mean that properties (e.g. plasticity, recruitment, modularity) of the black box are not illuminated by otherwise illuminating method.
none of the above indicates that intelligence is a complex derivative of an ancestral state within humans. the evidence from development indicates quite the opposite -- at this point i'll demure and recommend reading the most recent material on "neural crest cells" one can obtain. the trend in vertebrates is cranial specialization and in primates that meant strengthening sutures to support a wave of selection on increasing force of mastication which by way of a common developmental mechanism led to an "unrequested neuron surplus" enabling novel behavior worth selecting.*
this points to the second flaw in the quoted text -- traits that define vertebrates as a clade are not at risk such that mitigation of the mutational threat necessitates catastrophic-failure control vectors in humans. i'm consistently amazed that people still use the term "pleiotropy" and baffled still when it's intended as serious threat. i'm going to go out on a limb and say that the threat of pleiotropy is a theoretical solution to a theoretical problem completely counter-indicated by the biology being modeled. compound control is a native characteristic of biological control which enables regulation (rather than demonizing regulation in the style of pleiotropy). at this point i must direct those in the target audience (i.e. the outspoken instigator in the OP) to turn in their gun, badge, and license to the word "gene" as collateral on a mandatory loan of Simon Carroll's two books "Endless Forms, Most Beautiful" and "Making of the Fittest", with a probationary restriction on use of the term "complexity" within one clause of all formal generalizations past and present.
in a better world, aversion bias to a human-centric theory of biology would be sufficient to remind everyone involved that there are more important avenues of inquiry than intra-species vitriol.
*: the cognitive scientist in me is unable to omit a mention of the bland to banal homogeneity of representational structures that enable intelligence in humans. if intelligence is emergent and the emergence is the complexity then by definition the reduction is not complex.
The transracial adoption literature certainly doesn't support you, Greg.
Actually, it does. I have deal with that elsewhere.
Regarding the other adoptions studies you cite, mainly your' getting your interpretations quite wrong. After all, how do you get a zero correlation and still be of the same species? Jason, are you the crazy person who gave me all these same arguments over on my blog??? Read before you cite, young man.
Not that this will help. There is a reason that you need there to be a difference between people's intelligence based on their skin color. I can't help you much with this need of yours. I'm kinda busy.
After all, how do you get a zero correlation and still be of the same species?
I've read some of your rants before and thought you were a cunning liar. Now I've changed my mind -- you're just too stupid to figure things out.
Here's how you get a zero correlation. Make a scatter-plot of the IQ of adopted children, on the vertical, and the average IQ of their non-genetic adoptive parents (the mid-parent value), on the horizontal. Units are dimensionless z-scores. You would see a cloud that had no clear upward or downward trend, and that would be confirmed by the slope of the best-fit line (i.e., the correlation coefficient) being nearly 0 -- a flat line through the scatter.
That means that as you look at smarter adoptive parents, their adopted children are smarter as often as they are dumber, compared to the mean of all children.
Greg if you are citing Lewontin's book after all these years then you certainly have not "dealt with that elsewhere" in a long time.
There is a lot of data around these days and no support anywhere for the position you espouse. You should at least read Ian Dreary's textbook: his inclinations are like yours and he is straight honest: he concludes there is "no hope" or some phrase like that for any environmentalist position.
I remember reviewing Lewontin's book for some journal, memory fuzzy because it was a long time ago. I do remember that the data he cited about this did not support his position at all: I concluded he was either very very careless else really dishonest.
Henry
Actually, it does. I have deal with that elsewhere.
I know more about this literature than probably anyone else on earth. Actually it doesn't.
Reading biased summaries by Richard Lewontin or Richard Nisbett does not qualify your judgment. This is evidenced by your failure to know about the Tizard follow-ups.
For example, there is a new study published just last month from France, finding adoptees from Africa performing poorly in school, and adoptees from Asia doing far better than the French population. These kinds of studies exist in a lot of countries now.
After all, how do you get a zero correlation and still be of the same species?
Hahahaha. That's pretty sad, man.
The correlation indicates none of the variance in IQ scores between the adoptees was explained by the specific household in which they were placed, or by the particular parents they were placed with. See the chart in the income link. Adoptees from families that made $20,000 a year were no more likely to earn a higher income as adults than adoptees places in homes that made $200,000 a year.
Greg, exactly that kind of study *has* been done for things like hypertension risk. The only reason it "can't" be done is that nobody will fund it.
http://www.nature.com/ng/journal/v37/n2/abs/ng1510.html
Protip: having read Dick Lewontin does not, in fact, equip you to express an intelligent, informed opinion on this subject.
"After all, how do you get a zero correlation and still be of the same species? "
That's an odd statement.
More admixture mapping papers:
Tian C, Hinds DA, Shigeta R, Adler SG, Lee A, et al. (2007) A genomewide single-nucleotide-polymorphism panel for Mexican American admixture mapping. Am J Hum Genet 80:1014-23.
Reich D, Patterson N, De Jager PL, McDonald GJ, Waliszewska A, et al. (2005) A whole-genome admixture scan finds a candidate locus for multiple sclerosis susceptibility. Nat Genet 37:1113-8.
It's not how much different populations differ genetically, but in how they differ.
Whereto I.Q.
So fucking what? The study is about quantitative genetic differences, doesn't deal with intelligence at all. Studies dealing with group differences in intelligence are irrelevant to this discussion. That certain parties saw this thread as an opportunity to blather about their pernicious bete noir tells me more about them than it does about the subject of I.Q.
As a philosopher, let me pose a typical philosophical question: what if there are substantial differences between races when it comes to intelligence?
What kinds of responses might we have to such a question, politically and philosophically? What are the implications? What are the concerns over these implications? And are the scientists conducting the studies the only ones equipped to answer this question?
What concerns me is we're confronting this question in a piecemeal fashion, on blogs such as this, with opinions already laden with ideological baggage; we're arguing at a high level, ignoring that many of the differences in opinion occur at an unexplored lower level.
Perhaps we should explore the broad implications of racial differences outside of the scientific arena, and let the science inform us on which theories are more likely to be true.
That's not to say scientists shouldn't have opinions on these issues, nor engage in ideological debates - but just that arguing about results because of ideological differences on a science blog is a clumsy way to make a very important philosophical and ideological point.
For anyone who is still not sure how intellectually dishonest Greg Laden can be, two quotes follow.
Greg on his blog:
"There is no such thing as race (biologically)"
http://scienceblogs.com/gregladen/2008/10/the_science_museum_of_minneso…
Greg on Sandwalk blog comments:
"It is absolutely silly to pretend that races don't exist".
http://sandwalk.blogspot.com/2008/11/greg-laden-on-race-again.html
So when he says that he "dealt with it elswhere" - don't believe. He didn't. No references, just proclamations.
Tim, I think it would be interesting to get people to be explicit about what they think the implications would be, because I suspect a lot of the fear is unwarranted. I'd be willing to hazard the strong position that there are no implications at all.
Speaking for myself, it's a question that's scientifically interesting to the extent that it gives us ideas about how to boost intelligence. But beyond that, so what? The facts never change anyone's mind when it comes to politics -- ideology is often called rigid but it is, in fact, remarkably flexible. That's why certain people's willful obscurantism on this subject is so infuriating -- "the truth shall set you free".
Getting back to your original (rhetorical) question Razib about "What am I missing here?" I would say you're not missing anything. As you suggest, you can model a complex trait as a trait controlled by one or a few QTLs of large effect (even though most QTLs actually seem to explain little variation) and show that 50,000K generations is more than enough time for selection to act.
But as to the effects of migration swamping out local adaptation, this is a problem that is based on the parameterization. Local adaptation is a reality of human evolution (e.g., skin color) as is migration. Whether one swamps out the effects of another is a matter of figuring out the selection coefficients versus the migration rate. Period.
Finally, the comments here seemed to have moved away from the original question to the perennially unsolved but played-to-death topic of race/intelligence/heritability.
Henry, I'm not up on this IQ-heritability literature, but there is a section on this topic by Vissher et al., in "Nature Reviews Genetics 2008." In this section, they discuss some studies of IQ and heritability, though I'm not sure if the studies they cite are recent or robust. But that might be a place to start.
As to the whole idea of race and genetics, I'm actually having a lot of trouble buying the results of the studies by Rosenberg et al., and Bamshad et al. These were the studies that claimed to show how microsatellite and Alu variation in particular human groups mapped on to geographic variation, often showing that there are 3 to 5 clusters in the data that correspond to some of the classical geographic boundaries of human groups: Europe, Asia, Africa (and Oceania). These programs rely on the black-box use of the program STRUCTURE. This Bayesian clustering program has lots of problems. The manual even says that when the data follow an isolation-by-distance pattern, the results will be "arbitrary." Further, Deborah Bolnick did some follow-up exploration of the Rosenberg data and she reported (via a pers comm. from Rosenberg) that STRUCTURE produced results of equally high likelihood that showed there were 16 clusters in the data, not 5 as was reported in the original paper. The recent review on race/genetics by Bamshad et al. (in Nature Reviews Genetics) is also a bit problematic. They use some genetic data to show that individuals can be assigned to Africa, Asia, or Europe with a very high probability. This was widely interpreted by the media to show that "races" have a genetic basis. But as pointed about by more than a few folks, their analysis presumes that these geographic areas a priori have some meaning. That is, the continental boundaries of these areas correspond to some biologically meaningful genetic boundaries. Don't get me wrong, the data by Bamshad et al., are robust, it's just that they shoe-horn their results into a framework of "genes for Africa" "genes for Europe" and "genes for Asia", which to me, presumes the these areas have intrinsic biological boundaries that are impermeable. Their problem arises because they have sampled across geographic space but present their results as an average probability of genetic dissimilarity between regions (i.e., between Asians, Africans, Europeans, etc.) but any two populations that are closer together (or further apart) will be more (or less) genetically dissimilar. This presentation reifies that these regions have some intrinsic importance, when in reality, the data show much more of a clinal or IBD pattern than was reported by the media.
what if there are substantial differences between races when it comes to intelligence? What kinds of responses might we have to such a question, politically and philosophically?
I haven't thought deeply about your questions, but I think they are important and legitimate questions to ask (as opposed to wishing them away by denying that any such differences do exist or could exist). One response would just be an echo of traditional thinking about the "lesser races" that justifies explicit government and societal discrimination and even government-mandated eugenic measures. A somewhat less crude version of this might, for example, deemphasize attempts by government to equalize spending on education since "it won't make a difference anyway". These sorts of things are what I presume liberals think are on the minds of conservatives who discuss "human biological differences". (I speak here of the assumption, not necessarily the reality -- I haven't read enough of the work of such conservatives to fully characterize it.)
Another response would be to try to re-orient government measures to focus solely on individuals as opposed to groups: recognize that group averages are not determinative of the fate of any one individual, and seek to maximize the potential of every person. As far as I know, this is the position of at least some of the conservatives who've written on this topic - an emphasis on the virtues of meritocracy and the need for government to ensure that any such meritocracy is established in a just manner.
However even in a meritocracy with equal opportunity people would still likely tend to identify themselves with their own racial and ethnic groups, and would be so identified by others. That then raises the possibility that effects like stereotype threat would work against the meritocratic goal by depressing individual performance below what it might be in an ideal neutral environment. (If I recall correctly, one of the commenters on Razib's blog once raised the possibility of an "iterated stereotype threat" effect that could magnify small between-group differences into large ones.) This possibility may underly the desire of many people to not even speak of possible between-group differences, lest this become a self-fulfilling prophecy. (I think William Saletan's "it's not race, it's genes" argument is a more sophisticated response to this concern.)
There are also other problems with a society organized solely on meritocratic lines, most notably the possibility of a meritocratic elite perpetuating itself unjustly through various means. (See for example Young's The Rise of the Meritocracy.) This concern also intersects with historical practices like restricting the franchise to property owners, imposing poll taxes, etc., many of which were in service to or at least associated with racial discrimination. (One modern variant of this is the "multiple vote" idea discussed in Nevil Shute's novel In the Wet and apparently seriously considered in at least one real-life case.)
I think in general many people are concerned that a focus on between-group differences in intelligence and other qualities affecting individual achievement (e.g., time preference or whatever) will in some manner lead to a weakening of our conceptions of everyone's inherent equality from a political, moral, etc., perspective. This concern is exacerbated by the fact that at least a few of the people arguing the reality of between-group differences are apparently racists of a fairly conventional type. (It should go without saying that I exempt Razib from this.)
However anyone interested in establishing a just society already has to account for the clear reality of individual differences in intelligence and other qualities at least partially hereditary, and I don't think adding between-group hereditary differences to the mix spells doom for this project. It does require careful thinking through of all the issues and implications, and I can understand people's frustration that such thinking through is perceived a priori as in some way illegitimate or invidious.
Rich Lawler, PCA doesn't use the explicit genetic models used in programs like STRUCTURE and still produces essentially the same results. For examples of PCA studies, see the many "maps" of Europe/Asia that Razib has posted. Inferring an individual's ancestry from genotype has moved from an academic exercise to a commercial product at this point (e.g. 23andme).
lol, thanks for your response. I was under the impression that PCAs of genes, when plotted over geography, produce clines; wasn't this the major point of the numerous figures in Cavalli-Sforza's big book? Don't get me wrong, I'm sure there are genetic variants that map tidily onto geographic areas, but a lot (not all) of the data on human genetic variation appears to be continuous. And the 1st PC (which summarizes a lot of the covariation among whatever alleles happen to be used in the analysis) rarely shows a disjunct pattern across space.
I'm not sure if you're implying that since ancestry determination has gone "commercial" it somehow means it is rigorous. I presume you don't. But either way, those ancestry tests are pretty error prone and can't pin-point one's ancestry as accurately as they claim. I'm sure they'll improve over time, but for now they are motivated more by money than by rigor. It doesn't help that as we go back in time, the number of ancestors we have increases exponentially. In generation 10, one of my 1024 ancestors might be Ethiopian and this might also be the signal that the tests pick up on, but I'm not certain if that would qualify me as African American.
Rich,
The PCA data show that there is essentially no overlap in the largest principal components between, e.g., Nigerian / Asian / European populations. This is not using any explicit genetic models -- just PCA analysis as far as I can tell.
See picture here:
http://infoproc.blogspot.com/2008/11/human-genetic-variation-fst-and.ht…
I don't usually comment here. I find the mix of commenters on this thread very strange -- some people have very strong opinions, yet give references that are 20 years out of date! Anyone who is interested in this subject has got to get beyond things written many years ago by Lewontin, Gould, Cavalli-Sforza. If that is your state of knowledge, you should not be posting authoritatively on this subject! Things are changing very fast thanks to the genomics version of Moore's Law.
Hey Steve, thanks for the link. Looks informative (does component 1 actually explain only 1% of the total variation in that data set?).
To be sure, (if you were referring to me), I don't think I was posting "authoritatively" on this subject, since I worded my response to lol as a question. I'm fairly up-to-speed on the some but not all of the genomics studies of humans. They continue to accrue at a pace that outstrips my ability to digest them thoroughly.
Rich,
I don't think I was referring to you, but in any case my comment was in poor taste and I regret/withdraw it!
Yes, the largest component is only 1% of variation. There are over 100 statistically significant PCA vectors identified in that study. But the integrated (total) variance accounted for is probably less than a few percent at most.
Related discussion here:
http://infoproc.blogspot.com/2008/12/resolution-of-genetic-population.h…
I don't think I was referring to you, but in any case my comment was in poor taste and I regret/withdraw it!
Sir,
Bravo! Such graciousness in this fallen age warrants note and praise.
Yours truly,
C. V. Snicker
DK, others: If you like my perspective on race and racism, which you clearly do, then you may enjoy this: Social Construction of Race: Social Construction of Race: The Dark Side of Social Status
I want to clarify what I meant in my original post, because the sentence quoted in this blog post doesn't my point that clear (but previous statements in my original post do get at my point more directly).
I'm trying to make a distinction between what geneticists call complex or quantitative traits (traits affected by different alleles of many different genes, with a quantitative range of phenotypes), and something I would call a physiologically complex (or complicated) trait.
Complex or quantitative traits include both height and intelligence. But I'm arguing that something like height is not physiologically complex the way intelligence is.
Here is what I wrote in the original post:
So, for example, in the case of height, you can imagine that it is easy for a single allele of large effect to reach high frequency in a given population, resulting in a fairly tall (or short) population.
I don't think that such a thing is very likely for intelligence, because, unlike what I think is the case for height, single alleles of large effect on intelligence probably also have large deleterious effects (like neurological disorders) - something like intelligence is so physiologically complex that it is much easier to 'break' with a large-effect allele than something like stature, where an allele that extends how long growth plates in your leg bones are active (for example) is unlikely to also have major deleterious effects.
And to get race-specific differences, given current human genetic variation, you need single alleles with large effects - thus you have genetic differences between populations in height and skin color, but not IQ.
This is essentially what geneticist Lynn Jorde says:
And to get race-specific differences, given current human genetic variation, you need single alleles with large effects - thus you have genetic differences between populations in height and skin color, but not IQ.
no you don't. but i'll post a follow up so that the discussion can continue.
I'd like to see some example in real human populations, because I'm not aware of any. But I'll wait and read your explanation in your future post