The Likelihood of Genetic Group Differences in IQ: The Black White Gap in IQ

I apologize in advance for the daunting length of this post. My sole excuse is that I should have made it still longer to cover the topic.

In dealing with any controversy, it’s usually healthiest to begin at the sticking point. On the question of the impact of biology on political ideology, it’s plain enough what that is: group differences in IQ in general, and the black-white gap in IQ in particular.

I believe the best evidence is that the black-white IQ gap is real, that IQ measures something basic about intelligence, and that the difference between the average IQ of blacks and the average IQ of whites is based in substantial part on genetic differences between the two groups.

I’ll focus on the claim regarding the substantial genetic basis for the IQ gap. The evidence is perhaps best summarized in the following sequence of papers. The series commences with an initial paper by Arthur Jensen and Phillipe Rushton, is followed by criticisms from some of the most prominent anti-heriditarians, and ends with a final response to their critics from Jensen and Rushton:

Rushton, J. P., & Jensen, A. R. (2005). Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law, 11, 235-294.

Sternberg, R. J. (2005). There are no public-policy implications: A reply to Rushton and Jensen (2005). Psychology, Public Policy, and Law, 11, 295-301.

Nisbett, R. E. (2005). Heredity, environment, and race differences in IQ: A commentary on Rushton and Jensen (2005). Psychology, Public Policy, and Law, 11, 302-310.

Gottfredson, L. S. (2005). What if the hereditarian hypothesis is true? Psychology, Public Policy, and Law, 11, 311-319.

Suzuki, L., & Aronson, J. (2005). The cultural malleability of intelligence and its impact on the racial/ethnic hierarchy. Psychology, Public Policy, and Law, 11, 320-327.

Rushton, J. P., & Jensen, A. R (2005). Wanted: More race realism, less moralistic fallacy. Psychology, Public Policy, and Law, 11, 328-336.

Another paper that responds to the most recent criticism of the hereditarian hypothesis, in the book “Intelligence and How to Get It: Why Schools and Cultures Count” by Richard Nisbett, is this paper, again by Jensen and Rushton.

Also a very good summary of the latest data regarding the black-white IQ gap can be found in Charles Murray’s article The Inequality Taboo, from 2005.

As these papers make clear, there exist any number of items of evidence that point to the conclusion that the black-white IQ gap is quite considerable, and its genetic basis substantial. It is of course that evidence considered in aggregate that most inescapably nails down those conclusions. Yet some items seem even standing by themselves quite powerful.

I would subsume that evidence under the rubric of “regression to the mean” effects. Jensen and Rushton in “Thirty years of research on race differences in cognitive ability”, linked to above, describe the phenomenon and some of the evidence:

Regression toward the mean provides still another method of testing if the group differences are genetic. Regression toward the mean is seen, on average, when individuals with high IQ scores mate and their children show lower scores than their parents. This is because the parents pass on some, but not all, of their genes to their offspring. The converse happens for low IQ parents; they have children with somewhat higher IQs. Although parents pass on a random half of their genes to their offspring, they cannot pass on the particular combinations of genes that cause their own exceptionality. This is analogous to rolling a pair of dice and having them come up two 6s or two 1s. The odds are that on the next roll, you will get some value that is not quite as high (or as low). Physical and psychological traits involving dominant and recessive genes show some regression effect. Genetic theory predicts the magnitude of the regression effect to be smaller the closer the degree of kinship between the individuals being compared (e.g., identical twin  full-sibling or parent– child  half-sibling). Culture-only theory makes no systematic or quantitative predictions.

For any trait, scores should move toward the average for that population. So in the United States, genetic theory predicts that the children of Black parents of IQ 115 will regress toward the Black IQ average of 85, whereas children of White parents of IQ 115 will regress toward the White IQ average of 100. Similarly, children of Black parents of IQ 70 should move up toward the Black IQ average of 85, whereas children of White parents of IQ 70 should move up toward the White IQ average of 100. This hypothesis has been tested and the predictions confirmed. Regression would explain why Black children born to high IQ, wealthy Black parents have test scores 2 to 4 points lower than do White children born to low IQ, poor White parents (Jensen, 1998b, p. 358). High IQ Black parents do not pass on the full measure of their genetic advantage to their children, even though they gave them a good upbringing and good schools, often better than their own. (The same, of course, applies to high IQ White parents.) Culture-only theory cannot predict these results but must argue that cultural factors somehow imitate the effect theoretically predicted by genetic theory, which have also been demonstrated in studies of physical traits and in animals.

Jensen (1973, pp. 107–119) tested the regression predictions with data from siblings (900 White sibling pairs and 500 Black sibling pairs). These provide an even better test than parent– offspring comparisons because siblings share very similar environments. Black and White children matched for IQ had siblings who had regressed approximately halfway to their respective population means rather than to the mean of the combined population. For example, when Black children and White children were matched with IQs of 120, the siblings of Black children averaged close to 100, whereas the siblings of White children averaged close to 110. A reverse effect was found with children matched at the lower end of the IQ scale. When Black children and White children are matched for IQs of 70, the siblings of the Black children averaged about 78, whereas the siblings of the White children averaged about 85. The regression line showed no significant departure from linearity throughout the range of IQ from 50 to 150, as predicted by genetic theory but not by culture-only theory.

What is peculiarly compelling about this evidence? The simplicity and directness with which the genetic hypothesis accounts for the data, the accuracy of that prediction across the range of IQs, and the sheer implausibility of any primarily environmental account of that data.

Of course, those promoting the primarily environmental hypothesis can put together a response that formally meets the objection: some unknown factor X that depresses the IQ of all blacks effectively uniformly across the range, imposing a nearly exactly one standard deviation hit on each black subject measured. Now, I must say this purported effect impresses me as quite magical and unprecedented. What other socioeconomic or cultural environmental factor can one think of that induces such a uniform effect across such a range on a group of human beings?

Given what the factor X is supposed to effect in particular, how plausible is its existence? Wouldn’t one expect that some black families in some more environmentally propitious situations would enable their children to escape, or at least significantly to avoid, any factor X that might depress IQ scores? How is it, then, that even for black children with relatively high IQs of 120, their siblings should average only 100, rather than 110, as with the siblings of white children with IQs of 120? Consider the parents of a black child with the relatively high IQ of 120. Wouldn’t one expect that that family, which had managed to find and develop an environment congenial enough to the intellectual development of one of their children that he or she achieved an IQ of 120, might likewise have secured an environment as well suited for the intellectual development of their other children? Here we have the same parents, the same socioeconomic status, the same childrearing practices, as well as the same schools and neighborhoods. If environment means anything to IQ — which of course is the claim — shouldn’t such similarities be exactly what one would expect to engender the same kinds of outcomes in IQ? How explain then the great and otherwise unexpected disparity?

I find it very hard to ponder facts like these without inferring that genes dominate the explanation for the black-white IQ gap.

Another set of facts that I would categorize as “regression to the mean” effects is the disparity between black and white performance on the SAT even when controlling for economic status and level of education of parents. This is well captured in two graphs. (I take as a reasonable assumption that the SAT, which correlates as well with IQ tests as they correlate with each other, can here work as a good measure of IQ).
Average 1995 SAT scores vs income by ethnicity
Average 1995 SAT scores vs parental educational level by ethnicity

Both of these graphs run very hard against the hypothesis of purely, or dominantly, environmental basis of the black-white IQ gap. Yes, as parental education and income increase, SAT scores rise: that much an environmental explanation might predict. But, remarkably, the children of blacks whose income is over $70K attain an average SAT score lower than that of the children of whites whose income is well into the poverty level of $0K to $10K. Likewise, the children of blacks who had achieved a graduate level degree score lower on average on the SAT than do the children of whites who only finished HS.

How might one contemplate these items of data without feeling that they are exactly what one would not expect to see if environment played the major role in determining IQ differences between these groups? The advantages that come with a high income and with a graduate level education confer the very sort of benefits that are routinely said to explain why the average black student can’t do as well as the average white student on an IQ test or the SAT. How is it then that the effects of this relative privilege in black children cannot overwhelm, and easily, those of the clear deficts in the backgrounds of white students against whom the black childen are being compared? If income and educational level of parents entail so little, what can the environment plausibly be said to ground here?

Of course, this regression to the mean is, on the other hand, exactly what one would expect to see if the genetic basis were dominant in determining IQ or SAT scores. The hereditarian hypothesis predicts this and the earlier IQ data neat as a pin.

Now, again, one can contrive an explanation that lets the primarily environmental explanation off the hook. One can say that blacks at any income level and at any level of education suffer from a “caste mentality” or from “stereotype threat” which systematically undermines their performance. I plan to address those issues in more detail in a later post. For now, suffice it to say that the only likely motivation I can see to adopt such a view is to save the primarily environmental thesis from otherwise incompatible data. It appears to me to be a posit born of desperation: a scientific Hail Mary thrown up when the game is otherwise lost. In practice, it appears to operate as little more than a fudge factor X whose impact and exact size is determined only by what otherwise can’t be explained under a given hypothesis.

I think, though, that if one doesn’t divert one’s attention from the basic facts being communicated by these graphs and the earlier example described by Jensen and Rushton, and allows oneself to stare into this sun long enough to take its reckoning, then the natural conclusion is that it is genetic, rather than environmental, differences that are more basic to the black-white IQ gap.

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33 responses to “The Likelihood of Genetic Group Differences in IQ: The Black White Gap in IQ

  1. Welcome the HBD-osphere!

    Just those SAT graphs alone should convince anyone of HBD. Even though you’re a fricking liberal, I look forward to hearing what you have to say.

    Some tips:

    -Your template looks like shit. Get a new one.
    -Put up a blogroll of other HBD sites.
    -Post every day.
    -Comment on other HBD blogs (like mine) to get readership, especially HS and iSteve.

    • Congrats and good luck. And to reinforce the fourth of OneSTDV’s points, I found you when you commented on iSteve.

  2. I won’t pretend to be an expert of site design, but as a fellow wordpress.com blogger, I can point you in the right direction regarding how to address the first of OneSTDV’s tips.

    You can change the theme of your blog under the appearance menu which is on the left hand side of your dashboard, which you can access at the top of the page at this url:

    http://liberalbiorealism.wordpress.com/wp-admin/index.php

    And while I’m throwing out urls, the url for themes is as follows:

    http://liberalbiorealism.wordpress.com/wp-admin/themes.php

    Note that you need to be logged in for any of this to work.

    Your current theme is Kubrick, the default WordPress theme and you still have the “Just another WordPress.com weblog” subtitle that comes standard with a new blog. If you plan on being a long term blogger, I would suggest at least customizing Kubrick if not ditching it altogether for another theme and change or remove the subtitle, which you can do under general settings, which has the following url:

    http://liberalbiorealism.wordpress.com/wp-admin/options-general.php

    As for OneSTDV’s other tips, they seem pretty sound if you are are a serious blogger (I am not), as your main audience will be in HBD blogs, but I suspect that you already know that. That said, best of luck and I look forward to seeing your first post that integrates the liberalism with the biorealism.

  3. I share your point of view. The facts of human diversity are a moral challenge to liberals, as is the prospect of a racially-stratified class society.

    I think Charles Murray hit the right note in the final chapter of The Bell Curve, which he entitled, “A Place for Everyone,” You might have a look at if you haven’t already.

    The basic idea is that everyone’s happiness is equally important and equality of opportunity by itself is not enough.

    I’ve tried to imagine what a just society might look like from the point of view of the untalented nine-tenths. Google The Soft Path and it should come up.

    I wish you luck.

  4. I am also a liberal who has seen the writing on the wall regarding HBD. I am particularly interested in HBD related to alcoholism and other addictions. Why, for example, do aboriginal people in Canada and Australia, and Mongolia have exceptionally high rates of alcoholism?

    The racial-addiction link seems to be just as taboo as the racial-IQ link. Perhaps if the racial-addiction link were to be studied instead of ignored or hidden it might give clues that would lead to effective treatments for addiction that would benefit all races.

    I’m glad to have discovered your blog.

  5. Nice groundwork. Regression to the mean was the cincher for me as well.

    Anyway, I’m looking forward to seeing where this goes. I expect Rawls will come up sooner than later.

  6. Welcome! Good luck with this. I’ve been wanting to see a liberal analog of Steve Sailer for a while…

  7. Are you lurking on Richard Dawkins? Why not ask Lazar whether he agrees in principle with Watson’s statement that

    “there is no firm reason to anticipate that the intellectual capacities of peoples geographically separated in their evolution should prove to have evolved identically”

    Also, in terms of Watson’s retraction note the actual comments he made as Jason Malloy points out:

    “To those who have drawn the inference from my words that Africa, as a continent, is somehow genetically inferior, I can only apologise unreservedly. That is not what I meant. More importantly from my point of view, there is no scientific basis for such a belief…

    The overwhelming desire of society today is to assume that equal powers of reason are a universal heritage of humanity….

    To question this is not to give in to racism. This is not a discussion about superiority or inferiority, it is about seeking to understand differences, about why some of us are great musicians and others great engineers.
    Watson would only be retracting his intelligence claims if he considered those claims tantamount to claims of ‘superiority’ or ‘inferiority’, which he clearly emphasizes he doesn’t. Watson is saying that questioning that all races are equal in intelligence is not racism, it is trying to figure out why the world looks the way it does, with the greatest engineers and the greatest musicians disproportionately coming, in a systematic way, from different racial backgrounds. In other words culturally separated people of African descent have been musical innovators across a diverse range of cultures (in the Middle East, Africa, Europe, North and South America, and the Caribbean), while culturally separated people of East Asian descent have excelled at math and science across a diverse range of cultures (in Asia, Europe, North and South America, and the Caribbean).”

    (Jason Malloy) “This is not a claim of racial ‘superiority’ or ‘inferiority’, either in terms of legal worth or even in terms of overall talent – since groups all have different strengths and weaknesses. It is simply the recognition that people of different genetic heritage, on average, reveal different talents wherever they are found in the world, and there is one explanation that best accounts for these observations: evolution.

    In other words, Watson was thinking like a scientist. Which is exactly why he was punished.”

    http://www.gnxp.com/blog/2007/10/james-watson-tells-inconvenient-truth_296.php

  8. Regarding Lazar’s comment:

    ***In any case it is equally the case that research suggests gaps in IQ have closed from 15 point down to single figures in recent years and that gaps in achievement tests have gone from 1.1 SD to .65 SD. ***

    This is incorrect as addressed by Rushton & Jensen in their 2006 paper replying to Flynn & Dickens and the book review of Nisbett’s book you have cited.

    ***In addition, the research on herditability of IQ is advancing rapidly (see here). The old models of linear combinations of inheritance, shared environment, and unique environment have been found to be lacking. In essence it seems more likely that inheritance and environment and their effect on IQ is non-linear. Indeed, in the model I pointed to the results suggest that the herditability of IQ may differ wildly depending on SES. “The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes is close to zero; in affluent families, the result is almost exactly the reverse.” – from linked article. This makes the whole idea of assigning causes for IQ differences to inheritance alone extremely dubious.***

    The Turkheimer study is an outlier. In Britain, the exact opposite of Turkheimer’s result was found in over 2,000 pairs of 4-year-old twins (N = 4,446 children), with greater heritability observed in high-risk environments . A re-analysis of the Hawaii Family Study of Cognition also found contrary results to Turkeimer’s. Nagoshi and Johnson found no reduction in the relationship between parental cognitive ability and offspring performance in families of lower as opposed to upper levels of socioeconomic status. In the 1,349 families they studied, the relationship remained the same across tests, ethnicity, and sex of offspring. (see Rushton Jensen review of Nisbett).

    Also, in relation to Turkheimer’s study:

    1 – The study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid. The effects of the shared environment vanish at around age 12.

    2 – Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.

    3 – Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.

    4 – Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no adult IQ correlation between biologically unrelated children who were reared together in the same home.

    5 – Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used “cannot determine which aspect of SES is responsible for the interactions” observed.

    As for the reason the shared environmental component vanishes there are a number of possible reasons that are not yet sufficiently investigated to establish proof of causation.

    ***All of this however, is hand waving over the biggest problem of all. That is that variance in IQ is far greater within groups than between groups. As many have said already, race is a socially constructed phenomena and individuals within ‘racial classes’ are NOT homogeneous. It seems to that until research can show group differences predict differences in IQ AFTER controlling for the individual level (and can construct a meaningful definition of race) it should be treated as a statistical artifact ONLY. ***

    Like adolescence, race is a sociological and also biological phenomenon. There are readily identifiable clusters of points, corresponding to traditional continental ethnic groups: Europeans, Africans, Asians, Native Americans, etc. (See, for example, Risch et al., Am. J. Hum. Genet. 76:268–275, 2005.)

    Two groups that form distinct clusters are likely to exhibit different frequency distributions over various genes, leading to potential group differences.

    Most phenotypes (examples: height or IQ, which are both fairly heritable, except in cases of extreme environmental deprivation), there is significant overlap between different population distributions. That is, Swedes might be taller than Vietnamese on average, but the range of heights within each group is larger than the difference in the averages. Nevertheless, at the tails of the distribution one would find very large discrepancies: for example the percentage of the Swedish population that is over 2 meters tall (6″7) might be 5 or 10 times as large as the percentage of the Vietnamese population. If two groups differed by, say, 10 points in average IQ (2/3 of a standard deviation), the respective distributions would overlap quite a bit (more in-group than between-group variation), but the fraction of people with IQ above some threshold (e.g., >140) would be radically different.

  9. Some other interesting comments on the Turkheimer study and restriction of range issues by GNXP commentator Tango Man:

    “Consider the Turkheimer study. They separated out, and studied separately, the cohort of low IQ subjects and determined that nature played a smaller role in determining IQ than it did when compared to the larger group from which these subjects were drawn. Anyone familiar with statistical methods will recognize that this study is prone to restriction of range issues….

    What Turkheimer’s study does is kind of the same thing. We know that SES is highly correlated to IQ, same with race. By restricting his range in the way he did he minimized the role of genetics and inflated the role of environment. He wasn’t dealing with twins whose IQs ranged from 70-140, rather he was likely dealing with twins whose IQs ranged from 70-100, for keep in mind the fact that IQ, as an independent variable is correlated significantly to the dependent variable of SES, therefore the children born to low SES parents are also inheriting their, generally, lower IQ. By studying subjects in such a narrow range of course we would expect the influence of environment to rocket upwards.”

    http://www.washingtonmonthly.com/archives/individual/2006_07/009231.php#927965

  10. Looks like you were providing too much rational argument for the hereditarian position so Richard Dawkins’ had to ban you.

    Nice way to silence heretical views. The irony of that site is that they claim to embrace Darwin’s theories in preference of religion, but cling to their own religion of biological egalitarianism. Crazy.

  11. Interesting concession someone makes here though:

    “It’s really not that simple though in some ways : / his arguments appear reasonable to many people and they’re hard to disable unless one rejects notions of race and generalised intelligence (as people should ). “

  12. Pingback: New Liberal Race Realist Blog « Robert Lindsay

  13. Liberal Biorealist,

    Your common sense is needed in this discussion.

    http://boards.straightdope.com/sdmb/showthread.php?t=556158

  14. Enoch Powell Was Right

    “Likewise, the children of blacks who had attained a graduate degree score lower on average on the SAT than do the children of whites who only finish HS.” — I dare you to say that on the U.C. Berkeley campus.
    I double dare you to go to Berkeley and say that Mohammed of Mecca was a murderer .

  15. Transracial adoption has significantly increased in the past decades. Do adoptive parents (who are largely white) have anecdotal experiences with differences in their non-white children? If so, it seems not to deter white couples from adopting such children.

  16. If I were hired to do battle against the race realist position, I would begin by showcasing black geniuses from around the world, by which I mean blacks (not Caucasians who are ca 10-20% black, not mixed-race individuals like Obama, but individuals who are as close as possible to 100% African genetically) who have IQs above 145 or so, and who have impressive scientific or other achievements to their credit.

    I am not been polemical, I simply want to know:

    do such individuals exist?

    who are they, and where are they?

  17. @ elitist

    Google Philip Emeagwali. His IQ is believe d to be 190.

    Anything else?

  18. Pingback: A heretic in the high church of academia « Foseti

  19. Pingback: dispatches from TJICistan » Blog Archive » interview with Alan Dershowitz

  20. @ elitist

    Also google Thomas Mensah and Cheick Diarra.

  21. I cannot address all of this, but for now,
    just a couple quick thoughts:

    you write:
    “Of course, those promoting the primarily environmental hypothesis can put together a response that formally meets the objection: some unknown factor X that depresses the IQ of all blacks effectively uniformly across the range, imposing a nearly exactly one standard deviation hit on each black subject measured. Now, I must say this purported effect impresses me as quite magical and unprecedented. What other socioeconomic or cultural environmental factor can one think of that induces such a uniform effect across such a range on a group of human beings?”

    Why do you keep using the word “uniform”?
    If you are talking about average black I.Q., there
    is nothing “uniform” about it.

    As for “socioeconomic or cultural environmental
    factors” that can cause AVERAGE differences
    in various parameters, surely that does not
    require elaborate documentation.

    you write:
    “Given what the factor X is supposed to effect
    in particular, how plausible is its existence?
    Wouldn’t one expect that some black families
    in some more environmentally propitious
    situations would enable their children to
    escape, or at least significantly to avoid, any
    factor X that might depress IQ scores?”

    Maybe. But here we have to know what
    we’re talking about. What does “environmentally
    propitious” mean in specific terms? What are
    the factors that influence and determine brain
    development, response to environmental
    stimulation and education, and ultimately
    I.Q.? This is a very big question, with a very
    large literature spread across multiple
    biomedical and allied fields. There are MANY
    “factor Xs”, and they are increasingly less
    mysterious with the passage of time. At least
    “less mysterious” with respect to knowledge
    of their sheer existence. Still quite mysterious
    with respect to the (massive!) potentials for
    interactions, complementarities, etc. — almost
    none of which have been elucidated.

    I for one am not surprised a bit that blacks
    still have lower I.Q.s on average than whites.
    I would be surprised if it were otherwise.

    • liberalbiorealist

      Why do I use the word “uniform”? Because what I am describing is a uniform shift of the entire distribution of IQs downward by quite close to 1 SD in the case of African-Americans.

      The point is, it is not simply a matter of shifting down the average by 1 SD — which could, of course, in principle, be achieved with many kinds of distributions. But, in fact, the data shows an absolutely clear pattern of the uniform shift, so that, for example (and quite importantly), the tails — including the critical right tail — of the IQ distribution for African-Americans attenuate precisely according to the assumption of a normal distribution with a 1 SD lower average. Whatever the factor X may be, its ultimate effect must be to engender this uniform shift across the range. By far the most natural way in which that might occur would be for each individual African-American to be take a 1 SD “hit” in virtue of the effect of the hypothesized factor X.

      This uniform shift is simply remarkable if it is dominantly environmental in nature. Why should it work even within families, one wonders, so that siblings in AA families, for example, all regress to a mean of 1 SD lower than do siblings in white families? Why should the 1 SD hit work with rather little variation all the way across cultures that extend back to the Jim Crow era up to the present day, in which we have an African-American President celebrated for his brilliance? Why do we find this 1 SD shift not only in inner city neighborhoods, but also in upper middle class neighborhoods? Why do we see it both among HS dropouts and those with advanced degrees?

      The thing is, if the explanation of the gap is dominantly genetic, this uniform shift is exactly what one would expect to see; it simply falls right out of the hypothesis with no further ado. But if the explanation is an environmental Factor X, then one can hardly even begin to grasp what its nature might be. You see, it just doesn’t suffice to say that environment can affect IQ, and there’s some evidence for that proposition. What one needs is evidence for the very highly constrained, very specific sort of environmental effect I’ve described: something that works uniformly across all levels of IQ, apparently across all families, and pretty much across all cultures from the early 20th century to this very day. For that, there simply exists no real evidence. It appears to all the world to be nothing more than an ad hoc contrivance designed to save the environmental thesis.

      On the one hand, we have the utter simplicity of the explanation that invokes a dominantly genetic basis. On the other hand, we find only a highly elaborate (and which elaborations are otherwise ungrounded) explanation required for a dominantly environmental explanation. I ask: in these circumstances, and thinking as a scientist, how can one not favor the genetic hypothesis?

  22. PS: I just realized that I did not express myself
    well here: “If you are talking about average
    black I.Q., there is nothing “uniform” about it.”
    What I meant was that there is nothing uniform
    about black I.Q. scores, which are all over the
    map, just like whites’. “Uniform” is the wrong
    word, here. An average does not make for
    uniformity.

  23. Thanks for your lucid reply.

    you wrote:
    “This uniform shift is simply remarkable if it
    is dominantly environmental in nature.”

    I don’t see it that way. I’m not surprised. It is
    “remarkable” only if one isolates I.Q. from the
    myriad of environmental determinants of it.
    Looking at it in that manner — *in vacuo*, if
    you will — such patterns become “remarkable”.

    You wrote:
    “Why should the 1 SD hit work with rather little
    variation all the way across cultures that extend
    back to the Jim Crow era up to the present day,
    in which we have an African-American President
    celebrated for his brilliance?”

    The quick and easy answer is that Jim Crow
    never really ended; see Michele Alexander’s
    important new book The New Jim Crow:
    Mass Incarceration in the Age of Colorblindness.
    (And see several other volumes as well, but that’s
    a great start.) That is what I would call a
    “low resolution” answer; quick and easy, but of
    low resolution; “grainy”. In order to resolve the
    picture, one must make the connection between
    the racial disaster that Alexander (and others)
    describe, and neurobiology, and then I.Q. (to
    the extent that it relates to neurobiology, which
    I think is large). And that is a project that can
    hardly be undertaken in the comment box of
    a blog. But the project is well underway, I assure
    you.

    You wrote:
    “The thing is, if the explanation of the gap
    is dominantly genetic, this uniform shift
    is exactly what one would expect to see”

    Same if the explanation is dominantly
    personal and social psychological, and
    environmental, within the framework of
    racial caste as a social reality.

    You wrote:
    “But if the explanation is an environmental
    Factor X, then one can hardly even begin to
    grasp what its nature might be.”

    I agree that it is difficult — more difficult than
    the simple-minded “genetic” interpretation of
    things. Reality is complex, and difficult to
    comprehend at high resolution. That is
    the nature of it. I understand the appeal of
    simple explanations — God, genetics, and so
    forth. Such simplicity appeals to us because it
    spares us the hard work of long, deep study and
    comprehensive understanding, in a world where
    the literatures are vast.

    I do not agree, however, that “one can hardly
    even begin to grasp what its nature might be.”
    I think it is easy to BEGIN TO GRASP that;
    i.e. to imagine that. What is difficult is to go
    beyond the beginning, and really flesh the thing
    out in detail (as I say: at high resolution). THAT
    is difficult, yes.

    You wrote:
    “What one needs is evidence for the very highly
    constrained, very specific sort of environmental
    effect I’ve described: something that works
    uniformly across all levels of IQ, apparently
    across all families, and pretty much across
    all cultures from the early 20th century to this
    very day.”

    Again you speak of uniformity, but there is
    no uniformity, only average. The data points on
    the bell curve(s) are averages. Individual I.Q.s
    are all over the curve, for both races, but
    blacks AVERAGE lower. Thomas Sowell (for a
    quick example) probably has an I.Q. of at least
    150, maybe 160. Many other black intellectuals
    and scholars, same. But on average. blacks are
    lower.

    To me, the interesting question is not about
    a “uniformity” that does not exist, but about the
    diversity I just mentioned. How did those
    high-I.Q. black scholars get that way? And why
    is the average so much lower? And, of special
    interest to me: what are the precise or high-
    resolution material mechanisms that
    determine this diversity? For me, that question
    applies just as well to genetic mechanisms as
    to environmental ones. If I.Q. is influenced by
    genes, then what, precisely, are the mechanisms
    of that? Which proteins are the genes coding for
    that are relevant to I.Q.? Which enzymes or
    synthetic pathways are the genes influencing
    that are relevant to I.Q.? How can those genes
    be modulated (as all genes are) by environmental
    influences? What sort of epigenetic checks and
    controls are there on those genes? And so forth.
    I want facts, not black-box speculations.
    Unfortunately the genetic thesis is at this
    moment almost entirely a matter of black-box
    speculation — and not even USEFUL
    speculation. “It’s genetic!” We hear
    that so often, but it is almost meaningless,
    and fully useless. The same is not true of
    environmental effects, about which quite a
    bit is known, the pathways and mechanisms
    are being worked out, etc. And most of it is
    highly actionable; i.e. not useless.

    You wonder about a “very specific sort of
    environmental effect… that works uniformly”.
    Why would it have to work uniformly, in the
    context of a social situation in which racism of
    both individual and institutional sorts is still so
    rampant? I mean, given the impact of said racism
    on individual psychology — which in turn impacts
    performance on everything, not least I.Q. tests.

    Again I must stress that this word “uniform”
    is inappropriate. We are talking about averages.
    Of course the effects of any influence, be it
    environmental, psychological, or genetic, would
    not be uniform; it would vary, but the AVERAGE
    effect would show a pattern (a pattern that you
    are referring to — I think misleadingly — as
    “uniform”). In using the word “uniform” you
    seem to be implying that said effects are
    uniform on EACH INDIVIDUAL of a given
    group, and of course that is not true. That is
    not true of any influence — as I said, be it
    genetic or other. The bell curve describes
    average effects; the data from which the
    curve is derived is a big scatter-shot with
    dots all over the place — including e.g. Thomas
    Sowell way over on the right.

    • liberalbiorealist

      Let me try again.

      To begin with, my previous post, which I composed probably too late at night, didn’t really fully explicate what I meant by uniform.

      I defined it at first as the way in which a presumed Factor X would shift the entire curve of AA IQs, which would need to be close to uniform in how it applied to each individual. Now, that stands, but I also have in mind that the Factor X must be uniform in other ways, given the evidence: it must apply not just to IQs today, but to IQs in previous eras — going back to Jim Crow days. Likewise, given the evidence, it must apply uniformly to AA children who come from upper middle class backgrounds as well as to those all the way down the income ladder; it must apply as well to AA children of graduate educated parents all the way down to those whose parents are without HS educations. (See the graphs of SAT scores of whites and AAs in this post. The gap remains at pretty much the precise same size at each income level and each education level.)

      But let me return to the first point. You say that it’s not critical that the environmental effect hit each AA individual with a 1 SD effect, but only that the effect average across all individuals to 1 SD. That, however, is not true, given the shape of the shifted curve, which is exactly like that of the IQs of white children, save that it’s shifted 1 SD to the left.

      The problem is the tails — or at least the right tail, with which I’m most familiar. Suppose that the Factor X effect is, as you are assuming, on average of 1 SD, but that the effect is not simply of 1 SD, or very close to it, on every individual. Instead, let’s assume, there’s some real dispersion in how it hits different individuals. I claim that this, with some pretty obvious assumptions, leads to a result inconsistent with what’s known about the right tail.

      Suppose, for example, that the average effect is indeed 1 SD, but that there’s enough dispersion that, say, 20% of individuals experience essentially no effect. (To average out to a 1 SD effect, assume there is on the other side roughly 20% who suffer from a 2 SD effect.) Then, out at, for example, IQ 130 (which I assume is here 2 SD out for those unaffected by Factor X), the 20% of AAs who experience no Factor X effect will now have an IQ of 130, instead of a lower one. But how many such AAs will there be? Well, 2 SDs out or more, there are 2.27% cases; 20% of that is .45%. As just a rough further approximation, add to this (at minimum) those who suffer a 1 SD Factor X effect, and are shifted down from a potential 3 SD IQ to a 2 SD IQ — about .13% — and one gets .58% AAs at IQ 130.

      Here’s the rub: that (very approximate) figure is 4-5 times larger than what one actually sees at IQ 130 for AAs, because, in fact, the tails for AAs have essentially the exact same shape as that for whites, tails included, except shifted over by 1 SD (the predicted result of such a uniform shift would be the .13% [as opposed to the estimated .58%], which is very close to the actual result for AAs). The thinness of these tails (as expected in such a shape) is extremely well established. It is, in fact, essentially the only reason that such a major concession must be made in Affirmative Action at elite colleges and professional and graduate schools on such IQ-like tests as the SAT, the GRE, the LSAT, and the MCAT.

      Under natural assumptions, about the only way a Factor X might create a tail similar to what we actually see is if the dispersion of its effect is exceedingly narrow — so that it would be, indeed, quite fairly described as “uniform” in its application.

      Now, I supposed in my example that about 20% of AAs might effectively escape any real impact from Factor X. That, of course, was arbitrary, but similar results would come from smaller numbers.

      Probably the best way to handle various assumptions about the dispersion would be to use some modeling software to capture the ultimate effect, and to test it against what’s known about the right tail.

      Perhaps at some later point I’ll go through the effort of performing this exercise and posting the results.

  24. Pingback: Déterminants de la réussite scolaire : théorie ‘culture seule’ versus théorie héréditariste « analyseeconomique

  25. Hi, liberalbiorealist

    I just finished reading this paper.

    http://cscs.umich.edu/~crshalizi/sloth/lieberman-on-rushton.pdf

    Has Rushton (or Jensen, or Lynn) responded to Lieberman ? I can’t find anything about this.

  26. The whole hypothesis is thrown out of whack as the IQ test is a bit of a sham, devised by white psychologists appealing to white cultural programming and we can surely agree that many posessing a high IQ score can also demonstrate a pitifully low grasp of common sense; the first and last measure of intelligence or intelligent application.

  27. MH
    Following Lieberman’s paper itself, in the link you give, there are quite a few lengthy responses, including one by Rushton (page 85-86).

  28. I think you are incorrect about the importance of regression to the mean. It is easy to imagine environmental effects that regress – for instance, Jessica is raised to eat Wheaties, wake up at 8:00, and read an article in the newspaper every morning. Assuming that these are three keys to impacting IQ, why should we assume that these would be passed down to Jessica’s children? Imagining that two of the three make it to her kids, what is then the chance that those two would make it to her grandson Kyle?

    Every group shares and draws from a general cultural heritage. Individuals who deviate from it are likely to have children who return to it. For instance, it is seldom that the children of Texas atheists find Buddha, but common for them to find Christ.

    Let me add that I am a race realist, and I hold Jensen in high regard, but I value clear and objective thinking. So while it could be that I’m missing something, I believe that the regression to the mean argument is equally compatible with an environmentalist explanation. I urge realists to be careful before presenting it as a powerful support for their position.

  29. If you have studied Darwin, you’ll remember he made a pretty good argument that mankind evolved from many different linages, some species far more intelligent than others, and used that to reconcile the differences between races. In fact, he predicted that blacks would never be able to assimilate intellectually with whites and ultimately eliminated. I’m not sure we have all the information that’s needed in this study. Paleontologist keep finding new fossils that dismiss earlier theories that we thought were indisputable. However, your blog was a fascinating read.

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