Weak Evidence, Weak Argument: Race, IQ, Adoption

This post is a data dump for adoption studies and their analysis.

I found myself in yet another pointless debate with an uninformed person, a hereditarian in this case. I felt compelled to offer some info, even though I know from long experience that there is usually a reason for a person being uninformed while arguing strongly for a particular position. (I really need to stop getting into pointless debates, for I fear it is deleterious to my mental health.)

So, this post is in response to a ‘debate’ or rather that is what initiallly motivated my gathering all of this info and analysis. But my real purpose is to share all of this with others who actually might care to inform themselves.

My problem with this kind of data is as follows. It isn’t overly useful data in proving much of anything: small sample sizes, lack of effective controls and control groups, abundance of confounding factors, difficulty of replicability, etc.

We know through other research that racial biases are immense in our society, and this other research tends to be of a higher quality than the adoption (and twin) research. Studies have found various forms of racial biases in a wide variety of areas, from education to policing. It’s well supported that this is systemic and institutional.

It is also well supported that it is often internalized, and typically unconscious. Studies have shown that even minorities show prejudice against other minorities and that this is worse toward those with darker skin. Plus, studies show an internalized racial bias by way of stereotype threat, where the framing of a situation apparently causes the person to in a sense unintentionally sabotage themselves (because of added stress and cognitive load).

For any of these adoption (and twin) studies to be useful, it would require taking into account all the known confounding factors. I don’t know of a single study that does this or even attempts to come close to doing this. It would be ludicrously counterintuitive to presume that these endemic and internalized racial biases weren’t effecting the results.

All this leaves us is to speculate based on weak and probably misleading data. This means interpretation inevitably will follow ideology, as long as we limit ourselves to this data and ignore the larger context of data.

This is highly problematic, for the issues involved are complex. That is just the way reality is. If you want to deal with complex reality, you better find sophisticated ways of dealing with it. On that account, these studies fail in various ways. Still, they give us some possible insights in new directions to take with better research.

In conclusion, my basic point is that all of this demonstrates how weak is the argument being made by hereditarians. As for those who prefer environmental explanations, they don’t need this data at all, since there is already plenty of other data that supports their position. Given what we know, all of the racial disparities, IQ or otherwise, can be explained without recourse to genetic determinism.

This is an obvious statment, for the simple reason that race itself is a social construct, not a scientific fact. Social constructs and their social consequences need social explanations of social causes. The debate of the racial IQ gap is about as meaningful as attempting to compare the average magical intelligence of those sorted into each Hogwarts Houses by the magical sorting hat, if one were to base a society on such strange notions.

* * * *


“Whatever the final conclusion one would make, or would like to make depending on ideological inclinations, the samples are very small and most of the relevant informations on adoptees and adoptive/biological parents not available. None of the aforementioned studies provide full longitudinal information on adoptees and adoptive families. And yet, ignorant hereditarians cite this research as an established proof of racial genetic hierarchy. On the other side, however, I usually see that environmentalists have been trapped into the same fallacy as well. They cite transracial adoption data in support of their views without any care about 1) longitudinal data 2) biological parents’ characteristics. If adoption gain is empty in regard to g as was the case for educational intervention programs, we should expect vanishing gains over time. Besides, if shared environmental (c2) effects decrease over time, we may also expect vanishing gains. Hence the importance of follow-up data.”


“I have given examples of traits that are genetically determined but not heritable and, conversely, traits that are heritable but not genetically determined. Do these weird examples have any relevance to the case of IQ? Maybe there is a range of normal cases, of which IQ is an example, for which the oddities that I’ve pointed to are just irrelevant.

“Not so! In fact IQ is a great example of a trait that is highly heritable but not genetically determined. Recall that what makes toe number genetically determined is that having five toes is coded in and caused by the genes so as to develop in any normal environment. By contrast, IQ is enormously affected by normal environmental variation, and in ways that are not well understood. As Herrnstein and Murray concede, children from very low socio-economic status backgrounds who are adopted into high socio-economic status backgrounds have IQs dramatically higher than their parents. The point is underscored by what Herrnstein and Murray call the “Flynn Effect:” IQ has been rising about 3 points every 10 years worldwide. Since World War II, IQ in many countries has gone up 15 points, about the same as the gap separating Blacks and Whites in this country. And in some countries, the rise has been even more dramatic. For example, average IQ in Holland rose 21 points between 1952 and 1982. In a species in which toe number reacted in this way with environment (imagine a centipede-like creature which added toes as it ate more) I doubt that we would think of number of toes as genetically determined.”


“During World War II, both black and white American soldiers fathered children with German women. Thus some of these children had 100 percent European heritage and some had substantial African heritage. Tested in later childhood, the German children of the white fathers were found to have an average I.Q. of 97, and those of the black fathers had an average of 96.5, a trivial difference. . . .

“A superior adoption study — and one not discussed by the hereditarians — was carried out at Arizona State University by the psychologist Elsie Moore, who looked at black and mixed-race children adopted by middle-class families, either black or white, and found no difference in I.Q. between the black and mixed-race children. Most telling is Dr. Moore’s finding that children adopted by white families had I.Q.’s 13 points higher than those of children adopted by black families. The environments that even middle-class black children grow up in are not as favorable for the development of I.Q. as those of middle-class whites.”


“Another approach to these studies measures the IQs of black children brought up in white families. In one study of black, interracial, and white adopted children raised in white families, the white children showed the highest IQ scores, with interracial children scoring in the middle. But it’s not clear whether the white families treated the black children differently; whether the black children had suffered from IQ-reducing environments before they were born; or whether the older average age of adoption for the black children in the study prevented a fair comparison.

“Another study, of black West Indian (Caribbean) children and English children raised in an orphanage in England, found that the Caribbean children had higher IQs than those from England, with mixed-race children scoring in between. But were the black children given more attention by orphanage staff? Were particularly intelligent Caribbeans emigrating to England for better economic opportunity?

“Finally, a study of black children adopted by white versus black families in America showed that the black children raised by whites had higher IQ scores than those raised by blacks—suggesting an environmental cause. When the studies are taken together, the many caveats involved with the role of genetics and environment make it hard to draw firm conclusions. But the balance of data suggests no racial difference in intelligence.”


“Some skeptics have argued that scores on tests of this kind are really just proxies for family background. As we shall see, family background does affect test performance. But even when biological siblings are raised in the same family, their test scores hardly ever correlate more than 0.5. Among children who have been adopted, the correlation falls to around half that level. The claim that test scores are only a proxy for family background is therefore false. . . .

“Two small studies have tried to compare genetically similar children raised in black and white families. Elsie Moore found that black children adopted by white parents had IQ scores 13.5 points higher than black children adopted by black parents. Lee Willerman and his colleagues compared children with a black mother and a white father to children with a white mother and a black father. The cleanest comparison is for mixed-race children who lived only with their mother. Mixed-race children who lived with a white mother scored 11 points higher than mixed-race children who lived with a black mother. Since the black-white IQ gap averaged about 15 points at the time these two studies were done, they imply that about four-fifths of that gap was traceable to family-related factors (including schools and neighborhoods).

“A better-known study dealt with black and mixed-race children adopted by white parents in Minnesota. The mixed-race children were adopted earlier in life and had higher IQ scores than the children with two black parents. When the 29 black children were first tested, they scored at least ten points higher than the norm for black children, presumably because they had more favorable home environments than most black children. When these children were retested in their late teens or twenties, their IQ scores had dropped and were no longer very different from those of Northern blacks raised in black families. The most obvious explanation for this drop is that the adoptees had moved out of their white adoptive parents’ homes into less favorable environments. But because the study did not cover black or mixed-race children adopted by black parents, it does not seem to us to provide strong evidence on either side of the heredity-environment debate. . . .

“In theory, we can also separate the effects of parents’ socioeconomic status from the effects of their genes by studying adopted children. But because adoption agencies try to screen out “unsuitable” parents, the range of environments in adoptive homes is usually restricted. The adoptive samples for which we have data are also small. Thus while parental SES does not predict adopted children’s IQ scores as well as it predicts natural children’s IQ scores, the data on adopted children are not likely to persuade skeptics.”


“However, another set of observations have shown that there is a difference in the causes of variation within low SES and high SES populations. In low SES populations, environmental differences account for a larger degree of the variance than in high SES populations where genetic factors explain a larger portion of the variance. This is taken by Nisbett et al. (2012) to mean that high SES individuals are more likely to be able to develop their full biological potential, whereas low SES individuals are likely to be hindered in their development by adverse environmental conditions. The same review also points out that adoption studies generally are biased towards including only high and high middle SES families, meaning that they will tend to overestimate genetic effects. They also state that studies of adoption from lower-class homes to middle-class homes have shown that such children experience a 12 – 18 pt gain in IQ relative to children who remain in low SES homes.[23] . . .

“A number of studies have been done on the effect of similar rearing conditions on children from different races. The hypothesis is that by investigating whether black children adopted into white families demonstrated gains in IQ test scores relative to black children reared in black families. Depending on whether their test scores are more similar to their biological or adoptive families, that could be interpreted as either supporting a genetic or an environmental hypothesis. The main point of critique in studies like these however whether the environment of black children even when raised in White families are truly comparable to the environment of White children. Several reviews of the adoption study literature has pointed out that it is perhaps impossible to avoid confounding of biological and environmental factors in this type of studies.[118] Given the differing heritability estimates in medium-high SES and low-SES families, Nisbett et al. (2012:134) argue that adoption studies on the whole tend to overstate the role of genetics because they represent a restricted set of environments, mostly in the medium-high SES range.

“The Minnesota Transracial Adoption Study (1976) examined the IQ test scores of 122 adopted children and 143 nonadopted children reared by advantaged white families. The children were restudied ten years later.[119][120][121] The study found higher IQ for whites compared to blacks, both at age 7 and age 17.[119] Rushton & Jensen (2005) cite the Minnesota study as providing support to a genetic explanation. Nonetheless, acknowledging the existence of confounding factors, Scarr and Weinberg the authors of the original study, did not themselves consider that it provided support for either the hereditarian or environmentalist view.[122]

“Three other adoption studies found contrary evidence to the Minnesota study, lending support to a mostly environmental hypothesis:

“Eyferth (1961) studied the out-of-wedlock children of black and white soldiers stationed in Germany after World War 2 and then raised by white German mothers and found no significant differences.

“Tizard et al. (1972) studied black (African and West Indian), white, and mixed-race children raised in British long-stay residential nurseries. Three out of four tests found no significant differences. One test found higher scores for non-whites.

“Moore (1986) compared black and mixed-race children adopted by either black or white middle-class families in the United States. Moore observed that 23 black and interracial children raised by white parents had a significantly higher mean score than 23 age-matched children raised by black parents (117 vs 104), and argued that differences in early socialization explained these differences.

“Rushton and Jensen have argued that unlike the Minnesota Transracial Adoption Study, these studies did not retest the children post-adolescence when heritability of IQ would presumably be higher.[22][44] Nisbett (2009:226) however point out that the difference in heritability between ages 7 and 17 are quite small, and that consequently this is no reason to disregard Moore’s findings.

“Frydman and Lynn (1989) showed a mean IQ of 119 for Korean infants adopted by Belgian families. After correcting for the Flynn effect, the IQ of the adopted Korean children was still 10 points higher than the indigenous Belgian children.[123][19][124]

“Reviewing the evidence from adoption studies Mackintosh considers the studies by Tizard and Eyferth to be inconclusive, and the Minnesota study to be consistent only with a partial genetic hypothesis. On the whole he finds that environmental and genetic variables remain confounded and considers evidence from adoption studies inconclusive on the whole, and fully compatible with a 100% environmental explanation.[118] . . .

“Another study cited by Rushton & Jensen (2005), and by Nisbett et al. (2012), was Moore (1986) study which found that adopted mixed-race children’s has test scores identical to children with two black parents – receiving no apparent “benefit” from their white ancestry.”


“Compared mean IQ test performance and response styles to cognitive demands of the Wechsler Intelligence Scale for Children (WISC) among 23 Black children (aged 7–10 yrs) who had been adopted by middle-class White families (i.e., transracially adopted) and 23 age-matched Black children who had been adopted by middle-class Black families (i.e., traditionally adopted). Findings indicate that while the traditionally adopted Ss received normal IQ scores, transracially adopted Ss showed nearly 1 standard deviation Full-Scale Scoring advantage over them. A multiple analysis of variance (MANOVA) indicated significant differences in the styles of responding to test demands demonstrated by the 2 groups of Ss, which were conceptualized as contributors to the difference in average test score observed between them. Multivariate analysis of the helping behaviors adopted mothers exhibited when helping their children solve a difficult cognitive task revealed significant differences between Black and White mothers, which were conceptualized as culturally determined. White adopted mothers tended to release tension by joking, grinning, and laughing, while Black adoptive mothers more often released tension in less positive ways such as scowling, coughing, and frowning. White adoptive mothers were more likely than Black adoptive mothers to provide positive evaluations of their children’s problem solving efforts. It is concluded that the ethnicity of the rearing environment exerts a significant influence on children’s styles of responding to standardized intelligence tests and on their test achievement.”

* * * *

Education As the Cultivation of Intelligence
By Michael E. Martinez
pp. 102-3

“Of the research cited by Nisbett, only the Minnesota study on adoption provides any support for Hernstein and Murray’s claim that the Black-White IQ gap is genetic in origin. In this study, White (n=25) and black or mixed-race (Black-White) (n=130) children were adopted into White families (Scarr & Weinberg, 1976, 1983). When the subjects were older adolescents (mean age of 18.5 years), the adopted White children had the highest IQs (mean IQ=115.5), followed by the mixed race children (mean IQ=109.0), and then children of two Black parents (mean IQ=96.8). At first blush, it seems that this study supports the genetic doctrine. However, when the data are limited to Black children who were adopted before the age of 12 months, a different picture emerges. The average IQ of the Black early adoptees was 110, which was 20 points higher than the IQ of comparable children raised in the Black comunity, and 10 points higher than the population mean. For Black children placed before the age of 12 months, IQ correlations with adopted siblings were “embarrassingly similar” to those between natural siblings (Scarr & Weinberg, 1983, p. 264). It is true that the IQs of adopted Black children averaged 6 points below that of their White adoptive siblings, but this gap is small enough to be accounted for by differences in pre- and postnatal experiences prior to adoption. (IQ differences of 6 points or so are not unusual even among identical twins.) The same study showed that IQs of adopted children were more strongly correlated with their biological mothers (r=0.34) than with their adoptive mothers (r=0.21), reinforcing the belief that genetic forces are not to be dismissed; but these correlations are both rather weak, accounting for, at most 10% of the variance in IQ. More important, these correlations mask the upward shift in IQ enjoyed by the adopted children when compared to their nonadopted peers. Again, we are confronted with the statistical independence of measures of association (i.e., correlation and heritability coefficients) and the actual levels of measured ability (i.e., IQ and mental age). Thus, quite in contrast to the inferennces drawn by Hernstein and Murray (1984) in The Bell Curve, the original investigators concluded that “genetic racial differences do not account for a major portion of the IQ performance differences between racial groups” (Scarr & Weinberg, 1983, p. 261, emphasis added).”

Intelligence and How to Get It: Why Schools and Cultures Count
By Richard E. Nisbett
p. 30

“Because the environmental variation of adoptive families has mistakenly been assumed to be as great as the environmental variation in the population as a whole, the estimates of between-family environment effects are way off. Stoolmiller calculated that if you correct for this restriction of environmental range, as much as 50 percent of the variation in intelligence could be due to differences between family environments. Since we know that within-family variation also makes an important contribution to IQ, this would mean that most of the variation in IQ is due to the environment. (These numbers would hold, though, only for children. We know that heritability goes up with age to some degree, so Stoolmiller’s estimate for the contribution of between-family differences has to be lowered by some unknown amount.)

pp. 36-7

“The evidence we have just been looking at concerning the effects of genes versus the environment tells us something crucially important about social class and intelligence. The experiences of the children of the professional and middle classes result in much higher IQs and much lower school-failure rates than is typical for lower-SES children. Moreover, we can place a number, or at least a range, on the degree to which environmental factors characteristic of lower-SES families reduce IQ below its potential: it is between 12 and 18 points. Whatever the estimates of heritability turn out to be, nothing is going to change this fact. So we know that, in principle, interventions have the potential to be highly effective in changing the intelligence of the poor. Interventions could also greatly affect the rate of school failure of lower-class children. The minimum estimate for this reduction is about half a standard deviation. The maximum estimate for this is much higher— one standard deviation, or about the same rate that would be found for middle-class children raised by their own parents.

“Note also that it is not just the IQs of lower-SES children that can be affected. One study looked at the IQs of white children who were born to mothers with an average IQ and who were adopted by mostly middle-and upper-middle-class families. The children adopted relatively late had an average IQ in childhood of 112 and those adopted relatively early had an average IQ of 117. This study suggests that even children who would be expected to have an average IQ if raised in an average environment can have their IQ boosted very considerably if they are raised under highly propitious circumstances. Similarly, the cross-fostering study of Capron and Duyme showed that upper-middle-class children can have their IQs lowered if they are raised in poverty. The loss is about 12 points. So children born to poor families are not the only ones who can have their IQs dramatically affected by the environment. All children can.”

p. 98

“One way of testing the heredity-versus-environment question is to look at black children raised in white environments. If the black deficit in IQ is due entirely to the environment, then blacks raised in white environments ought to have higher IQs than those raised in black environments. The hereditarians cite a study from the 1980s showing that black children who had been adopted by white parents had lower IQs than white children adopted by white parents. Mixed-race adoptees had IQs in between those of the black and white children. But, as the researchers acknowledged, the study had many flaws; for instance, the black children had been adopted at a substantially later age than the mixed-race children, and later age at adoption is associated with lower IQ.

“A superior adoption study was carried out by developmental psychologist Elsie Moore, who looked at black and mixed-race children adopted by middle-class families, either black or white, and found no difference in IQ between the black and mixed-race children.”

13 thoughts on “Weak Evidence, Weak Argument: Race, IQ, Adoption

  1. I’m convinced such people are mostly trying to rationalize their own biases.

    I expect there to be a difference in intelligence, just like height, skin color, hair color, etc, but this should not be a reason for racism, which I get the impression many of these people are implying.

    • Yeah. There are, of course, differences in intelligence, as with everything else. Sure, genetics plays a factor in that. Few disagree with that much. The problem is how it gets interpreted.

      First, there is no way to separate genetics from environment, especially in terms of epigenetics; plus, the largely unknown role of so-called junk DNA. Even the complex interrrelationships between genetics is largely beyond our present knowledge. Very little involves a single gene and nothing else, and I doubt it is ultimately even meaningful to ever talk about singel genes in isolation.

      Second, the hypothesis that the genetics for skin color and other physical features correlates closely with the genetics of cognitive development is improbable to the point of absurdity. This doesn’t pass the smell test. To put it simply, no version of racial folk taxonomy matches what is scientifically known about population genetics. There isn’t any known genetic clusters that positively correlate to all individuals of one racial group and negatively correlate to all individuals in other racial groups. Heck, there isn’t even a single set of genes for skin color, as light and dark skin developed in several different places separately.

      I’m not saying anything radical here. This is the scientific consensus on this issue. Even the intelligent race realists will admit to this. They’ll just argue that there are ways of defining human races that do fit the scientific facts. That is fine as far as it goes, but they can only accomplish this by ignoring the issue that their newly created definitions no longer match what most people mean by human races. At that point, it just becomes a word game.

      What is most irritating are the less intelligent race realists who can’t admit the obvious. For them, it isn’t even a matter of playing word games. They are just plain ignorant and not clever enough to emply tactics of sophistry.

    • Immigrant scapegoating is a longtime favorite activity of Americans.

      It really doesn’t matter the race or ethnicity, religion or language. It doesn’t even matter if they really are immigrants or merely assumed to be.

      Any group that is perceived as foreign or different will do. Still, Mexicans and Hispanic-Americans have always been one of the most popular targets of scapegoating, even when their families have been in present US territory for longer than have Anglo-Americans.

  2. It seems to be far worse in the US than in other nations though.

    Perhaps this is due to the colonial nature of the US? Or is it somehow entrenched in the culture?

    It’s especially true in the Deep South.

    • When your immigrant ancestors participated in one of the largest genocides in world history and still maintain the descendants of survivors on reservations, it creates an uneasiness about the social order and about every new generation of immigrants.

  3. I wonder about that – most Americans do not have a good knowledge of history, so I’d wonder about whether apathy or simply a fear of the unknown causes racial tension as well.

    Plus American history education is seldom an objective source of knowledge.

    Compound that with a culture of existing bias and you have a disaster in the making.

    • Yep. Good articles. Poverty, debt, foreclosure, unemployment, and much else. These economic problems are the great equalizer. It’s what united Americans during the populist and progressive eras, even at times uniting people across various social divides (racial, ethnic, religious, regional, etc).

    • The very rich are using it though to exploit the culture wars for their benefit.

      Most conservative whites don’t seem to understand this – they blame “illegals”, blacks, gays and other scapegoats for their misfortunes.

    • The culture wars have been going on for a long time. The same basic culture war issues such as feminism go back the Enlightenment age and early modern revolutionary era. It changes form a bit, but surprisingly remains fairly consistent in many ways. For example, the Second KKK was all about the culture war issues and that was before the GOP became the right-wing party with the Southern Strategy.

      Even so, the recurrent culture wars can only do so much to suppress populist unrest and public outrage, once it has gotten to a certain point. The culture wars oddly even helped to promote the populist and progressive eras. The KKK supported universal public education, partly because of xenophobia about Catholic and ethnic schools. Mormons supported the New Deal.

      The culture wars tend to take a life of their own. Those that use such issues to manipulate people don’t always have as much control as they wish they had. A few generations later and the culture warriors sometimes end up attacking the very things the previous culture warriors helped put into place.

  4. It would seem then the GOP’s moves have left the political right with all of the drawbacks (racism) and none of the advantages – if even the KKK supported education. I’m not saying the KKK was good (I think it was a dark chapter in history), but even they did some good things.

    In the case of the Southern Democrats of old, even though they were racist, they did see at times a socially and economically progressive agenda. The new business Republicans have none of that.

    • That is sad. The bigots of past generations at least cared for the poor and disadvantaged of their own perceived group. There was racism involved in many progressive reforms, but at least it laid the groundwork for positive change that ended up often helping even originally excluded groups.

      It’s hard to see much good of any form coming out of present reactionary politics. However, that might change, as the white middle class and working class increasingly feel the pinch of economic problems. Populism has a way of using fear and outrage to fuel reform.

      You can sort of see the potential for this kind of thing in something like the Tea Party. In talking to Tea Party supporters, specifically my father and my second cousin, I’m hearing more support or at least openess toward more progressive ideas. Discontent about the status quo is growing, which can lead people to consider things they wouldn’t otherwise.

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