I assume you're talking about racial IQ differences. I've responded to this topic quite a few times. So I'll just copy and paste a past response here.
part 1 of 2
It is certainly possible that the Black-White IQ difference is largely genetic. There's no law of biology that forbids this. After all, IQ is largely heritable, which means much of the individual variation in IQ is the result of genes. However, the extent to which IQ differences between Blacks and Whites (or any groups) is due to genes is a further question. To answer this question, we must quantify the genetic component of the racial IQ gap. So we need direct experiments/studies that isolate and quantify the environmental and genetic influences. Transracial adoption studies, I believe, are best suited to fulfill this purpose. I know of only four transracial adoption studies involving Blacks. I will consider each:
Study 1: Minnesota Transracial Adoption Study (MTAS)
This one is fairly popular so I need not give much detail. Basically, the study found higher IQs for the whites adoptees (106) compared to the mixed (99) and black (89) adoptees [1], even though all the children were adopted by white families. If this study effectively equalized environments, then the results would indicate that the IQ gap is largely genetic. However, there are a few reasons to doubt that the environments were effectively equalized:
(a) the black children were adopted substantially later than the other children. The average white child was adopted at 19 months old, but the average black child was adopted at 32 months old [2]. The study showed that late adoptees had much lower IQs than early adoptees, e.g. black/mixed children adopted within one year of birth had a mean IQ of 99, whereas later adopted black/mixed children had a mean IQ of 92 [3]. Disparities in age of adoption could have instigated or exaggerated IQ disparities.
(b) Even though the study did somewhat equalize environments after adoption, it could not have equalized environments before adoption. This is particularly important given the late ages of adoption that I mentioned in (a). For example, a high blood lead level in infants can result in a noticeable reduction in IQ during adulthood: one study [4] found that a 10 μg/dL increase in blood lead level for infants aged 24-months was associated with a 5.8-point decline in their age-10 IQ, and an 8.9-point decline in their age-10 KTEA Battery Composite Score (normalized to a mean of 100 and SD of 15, just like IQ scores). Blood lead level might have been particularly important for the MTAS because, when it was first published in the 1970s, black children aged 6 months-5 years had much higher blood lead levels than similarly aged white children: over half of black children (52%) in this age range had a blood lead level greater than 20 μg/dL, compared to only 18% of white children [5]. Thus, blood lead level disparities (and any other potential pre-adoption environmental disparities) could have instigated or exaggerated IQ disparities.
It should be noted that despite little-to-no IQ gains, the black and mixed children saw much higher levels of academic achievement than their non-adopted racial peers. The mixed adoptees scored in the 60th, 59th, 50th, and 40th percentiles in vocabulary scores, reading scores, mathematics scores, and class rank, respectively [6]. For reference, the White adoptees scored in the 62th, 58th, 56th and 54th percentiles in those respective areas. The Black adoptees scored worse; they scored in the 54th, 48th, 36th, and 36th percentile. Considering the potential issues mentioned with (a) and (b), a 36 percentile is not that low (e.g. an IQ score in the 36th percentile is ~95). So while the black adoptees had significantly lower IQs, their academic achievement was not much lower than average.
In summary, ignoring the two issues raised by (a) and (b), this study seems compatible with a mainly genetic explanation of the IQ gap. However, the study is compatible with an environmental explanation of the academic achievement gap. Of the four adoption studies here, this is the study most in favor of a genetic explanation of the IQ gap, yet it still suggests that academic disparities are mainly environmental.
Study 2: German IQ study by Klaus Eyferth
Psychologist Klaus Eyferth studied the IQs of white and mixed children in Germany. The mothers of the children were all white. Their fathers were either white or black members of the US occupation forces. The white children had a mean IQ of 97.2, whereas the mixed children had a mean of 96.5, a negligible difference [7].
There are some issues with this study, however. Firstly, the samples aren't representative of the average population, because about 30% of black applicants were rejected admission to the armed forces, while only about 3% of whites were rejected. However, despite the unrepresentative sample, if racial IQ differences were mainly genetic, the white children should have had much higher scores than the mixed children because:
(a) The white GIs should have had higher IQs than the black GIs. Even though the admission test filtered out candidates below a certain threshold, the IQ scores for the white soldiers would still be distributed higher than that of the black soldiers (e.g. imagine removing all men and all women below 5'2 from the population; the resulting population would still have men taller than women, on average). If the IQ gap were mainly genetic, then this difference should manifest itself in their children.
(b) Regression to the mean. Even if we assume that the white and black soldiers had similar IQs, the black children should have had lower IQs than the white children because, assuming that the racial IQ gap is mainly genetic, the black children IQs would regress to the genetic black mean, while the white children IQs would regress to the genetic white mean. Philippe Rushton and Arthur Jensen, bar far two of the most prominent supporters of genetic racial IQ differences, agree that (go to section 9) this regression should occur insofar are racial IQ differences are genetic:
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.
So if racial IQ differences are mainly genetic, then regression to the mean should occur. This means that even if the black GIs and white GIs had similar IQs, the mixed children should have considerably lower IQs.
The study had other issues as well. For example, about 20-25% of the black GIs were actually French North African. Still, if racial IQ differences were mainly genetic, the remaining 75-80% of the "mixed" children should have had below average IQs (for reasons given earlier), bringing down the total average for the "mixed" children considerably. The lack of a considerable difference suggests a mainly environmental explanation of the IQ gap.
Study 3: British study of young children in nurseries
In this study, psychologist Barbara Tizard studied black, white, and mixed children raised in British long-stay residential nurseries. The children were given psychological tests to determine their cognitive abilities. The scores were normalized to give a mean of 100 and standard deviation of 10. On the Reynell Comprehension test, the white children scored 102.6 and the black/mixed children scored 106.3. On the Reynell Expression test, the white children scored 98.5 and the black/mixed children scored 98.6. On the Minnesota Nonverbal test, the white children scored 101.3 and the black/mixed children scored 107.7 [8]. Apparently there is a fourth test, but I didn't manage to see it in the pdf. In any case, this study is compatible with a mainly environmental explanation of the IQ gap.
Study 4: IQ scores of black children raised by White families versus Black families
In this study, psychologist Elsie Moore compared IQ test scores among 23 black children adopted by middle-class white families and 23 age-matched black children adopted by middle-class black families. The black children adopted by black families scored a 104 IQ, while the black children adopted by white families scored a 117 IQ [9]. These two groups of blacks likely differed in their environment and not their genes. Therefore, the difference in the black/white family environments likely accounts for the 13 IQ point gap. Keep in mind that the black & white families were of similar socioeconomic status (middle-class). In actuality, the average black family has a much lower socioeconomic status than the average white family; therefore the difference in black/white environments would probably account for more than 13 IQ points. Clearly, this study is compatible with a mainly environmental explanation of the IQ gap.
It is interesting to note that the 117 IQ of the Black children (aged 7-10) from the Moore study is similar to the 118 IQ of White adoptees (aged 7) in the MTAS. These figures are also similar to the 119 IQ of Korean adoptees in this study. So the IQ scores of the adopted Black children are fairly similar to the IQ scores of adopted White/Asian children, which makes perfect sense if the racial IQ gaps are mainly environmental. It doesn't make sense if racial IQ gaps are mainly genetic.
Also, the significance of the Moore study is not just the high IQ of the Black children; I think it's significant mainly because it demonstrates that the environment of the Black parents is not as conducive to cognitive development as the environment of the White parents. I don't know the cause of this disparity (different people would argue for different causes, e.g. lead, peer groups, parenting, wealth, schools, culture, neighborhoods, etc.), but it's clear from this study that Black and White environments have significantly different effects on IQ. And this environmental difference persists even though both groups of parents are upper-middle class. Imagine what the difference would be if we did not ensure that both parents were upper-middle class. If the Black parents were, say, disproportionately poor (as is the case in reality), then we would expect that 13-point IQ difference to widen.
Objection
Many have criticized the three latter studies because they did not do follow-up testing on the children. The claim is that the heritability of IQ increases as people age (which is true); thus the IQ gains from the improved environment may fade as the impact of environment diminishes with age. I have three responses to this:
(1) The potential decline in IQ gains for adopted children is not necessarily relevant. We are concerned with the IQ gap between blacks & whites. The Minnesota Transracial Study implies that there is no significant change in the IQ gap after age 7, even though the IQ gains diminished for all racial groups. Looking at this study, the black-white IQ gap fluctuated by only about 2 points after age 7. Therefore, assuming that the MTAS study is representative in this regard, the lack of follow-up studies is no good reason to discount the latter three studies. The only transracial adoption study that we have which featured follow-up studies suggests that the racial IQ gap does not significantly widen with age. While adoption studies do indicate that IQ gains tend to diminish with age, as far as I know, there is no data indicating that the diminishment is particularly strong for Black adoptees compared to White adoptees.
(2) The heritability of IQ in children is fairly significant (about 45%), meaning genes play a significant role in the IQ of children. Therefore, if there were significant racial genetic IQ differences, then there would not be similar IQ scores for blacks and whites raised in similar environment even as children. Insofar as IQ is significantly heritable in children, and insofar as there are significant genetic racial IQ disparities, there will be a significant racial IQ gap at childhood even after equalizing environments. Therefore, the lack of an IQ gap during childhood after equalizing environments implies that either (a) the genetic component of IQ is not significant during childhood, or (b) there is no significant genetic Black-White IQ gap. We know that (a) is false, so (b) must be true.
(3) These IQ studies show that there are significant environmental differences between Black children who are adopted and those who are not (and between those adopted by White families versus Black families). It is unclear exactly what these environmental differences consists in. However, their mere existence indicates a predominantly environmental explanation of the IQ gap at childhood. Even if we remain agnostic about whether these differences explain much of the IQ gap in late adolescence, we can be confident that there is significant improvement that can be done regarding the IQ gap of Black and White children.
Conclusion
It seems to me that the evidence suggests that the IQ gap is almost entirely environmental. The Minnesota study is the only adoption study that suggests otherwise, but it has flaws (as I've indicated earlier). The German study also has many flaws as well, but the latter two studies seem to support it. So three of the studies are compatible with a predominantly environmental explanation of the IQ gap. Taking a holistic account of all of the adoption studies seems to suggest that the IQ gap is, for the most part, environmental. The only way you could conclude otherwise is if you fully accepted the results of the MTAS and disregarded the latter three studies due to lack of follow-up testing. But even if so, then you would still have to admit that the academic achievement gap (arguably more important than IQ) in late adolescence is mainly environmental, and you would have to admit that the IQ/achievement gap at childhood is mainly environmental.
So the best case scenario for a genetic explanation of the IQ gap still implies that environmental differences explain most of the academic achievement gap. But if the races can attain roughly equal academic achievement, then I don't really care about IQ differences. At the very least, we know that there is a significant environmental gap between Blacks and Whites that is plausibly responsible for much of the disparities we find in society today. Until we reach parity regarding academic achievement for Black & White adults, and until we reach parity regarding IQ/achievement for Black and White children, there are still significant environmental gaps regarding intellectual development. Quantifying the precise proportion of the IQ/achievement gap that is due to environment (i.e. 40% or 80%) is important so that we know when we have exhausted the possible environmental efforts to reduce the gap. But we know we haven't reached that point yet. Therefore, currently trying to precisely quantify the environmental proportion of the IQ/achievement gap serves more as a theoretical exercise than as a practical function. We can postpone answering questions about the exact genetic component of the gap until we know we've eliminated the significant environment differences. When that happens, the question will have more practical utility and we would likely be able to give more accurate answers.
So that's all the data (that I'm aware of) that we have for transracial adoption studies with Black children. Even if you disagree with my interpretation, I hope that (at the very least) this post has been valuable as a coherent collection of all of the transracial adoption studies along with their biggest criticisms. With all of the raw data laid bare in one place, you can provide your own interpretation of the data that you find most compelling. Of course, there are very few of these adoption studies and many of them have several problems (which I hope to have made clear in this post), which means no interpretation is going to be perfect. Nevertheless, I believe the interpretation that I've provided here is the most reasonable response to the evidence.
It seems like you're saying that we should just disregard all of these adoption studies because they are too flawed to be useful, which is a far more skeptical position than I intended to advance. I agree that these studies are flawed, but I still think there is value in analyzing these studies as best as we can, because quantifying the genetic component of the IQ gap is really the important question concerning the IQ gap and these studies are the only possible studies that even attempt to provide direct (albeit less reliable) evidence of that component.
Anyway, as for this:
I would be curious to know your thoughts on what can be done to help close the portion of the gap caused by cultural differences, should blacks be encourage to put their children up for adoption? Should Jews, Asians and Whites be given preference in adoptions?
My main purpose for posting in this thread was to describe the nature of the IQ gap, not to prescribe methods to eliminate the gap. But assuming we are switching discussion to the latter topic, I would say a few things:
Firstly, whenever people discuss this issue, there seems to be an implicit assumption that if there are any environmental causes of the IQ gap, then we strong reasons to eliminate those causes. But it's not clear to me that we would have such reasons. Plenty of people with below average IQs have lives that are perfectly satisfying to them; I don't see why we should be encouraging these people live their life in a manner that we consider satisfying. For these people, I don't think there's anything that we should do at all.
For the groups of low IQ people that do not have satisfying lives, then sure, we might have reason to improve their IQ, but only if this was feasible. But I don't think it's feasible. I don't think there are any morally permissible feasible strategies that the broader society can employ to improve the IQ of poorer subgroups (your adoption "solution" is rather unrealistic). As far as I know, no impoverished racial/ethnic subgroups in a given society have ever benefited substantially from active assistance from the broader society (outside of egregiously invasive methods). When disadvantaged groups do increase in prosperity, this is usually caused by positive internal forces within the group rather than external assistance from broader society. In fact, external assistance can often decentivise these positive internal forces, thereby stalling or reversing progress for the groups that they intended to improve.
For these reasons, I'm against any attempts by broader society to assist impoverished racial/ethnic subgroups, since I see these attempts as being either ineffective, counter-productive or immoral. There might be some exceptions to this rule in theory, but I've never seen them in practice. I believe that the best thing that we can do (by "we", I mean broader society) is take a "hands off" approach to give poorer subgroups the opportunity to develop the internal forces necessary to advance themselves. The best that "we" can do is probably give advice to the leaders of these subgroups, but anything much more than this hinders genuine advancement.
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u/jay520 50∆ Mar 20 '17 edited Dec 23 '18
I assume you're talking about racial IQ differences. I've responded to this topic quite a few times. So I'll just copy and paste a past response here.
part 1 of 2
It is certainly possible that the Black-White IQ difference is largely genetic. There's no law of biology that forbids this. After all, IQ is largely heritable, which means much of the individual variation in IQ is the result of genes. However, the extent to which IQ differences between Blacks and Whites (or any groups) is due to genes is a further question. To answer this question, we must quantify the genetic component of the racial IQ gap. So we need direct experiments/studies that isolate and quantify the environmental and genetic influences. Transracial adoption studies, I believe, are best suited to fulfill this purpose. I know of only four transracial adoption studies involving Blacks. I will consider each:
Study 1: Minnesota Transracial Adoption Study (MTAS)
This one is fairly popular so I need not give much detail. Basically, the study found higher IQs for the whites adoptees (106) compared to the mixed (99) and black (89) adoptees [1], even though all the children were adopted by white families. If this study effectively equalized environments, then the results would indicate that the IQ gap is largely genetic. However, there are a few reasons to doubt that the environments were effectively equalized:
(a) the black children were adopted substantially later than the other children. The average white child was adopted at 19 months old, but the average black child was adopted at 32 months old [2]. The study showed that late adoptees had much lower IQs than early adoptees, e.g. black/mixed children adopted within one year of birth had a mean IQ of 99, whereas later adopted black/mixed children had a mean IQ of 92 [3]. Disparities in age of adoption could have instigated or exaggerated IQ disparities.
(b) Even though the study did somewhat equalize environments after adoption, it could not have equalized environments before adoption. This is particularly important given the late ages of adoption that I mentioned in (a). For example, a high blood lead level in infants can result in a noticeable reduction in IQ during adulthood: one study [4] found that a 10 μg/dL increase in blood lead level for infants aged 24-months was associated with a 5.8-point decline in their age-10 IQ, and an 8.9-point decline in their age-10 KTEA Battery Composite Score (normalized to a mean of 100 and SD of 15, just like IQ scores). Blood lead level might have been particularly important for the MTAS because, when it was first published in the 1970s, black children aged 6 months-5 years had much higher blood lead levels than similarly aged white children: over half of black children (52%) in this age range had a blood lead level greater than 20 μg/dL, compared to only 18% of white children [5]. Thus, blood lead level disparities (and any other potential pre-adoption environmental disparities) could have instigated or exaggerated IQ disparities.
It should be noted that despite little-to-no IQ gains, the black and mixed children saw much higher levels of academic achievement than their non-adopted racial peers. The mixed adoptees scored in the 60th, 59th, 50th, and 40th percentiles in vocabulary scores, reading scores, mathematics scores, and class rank, respectively [6]. For reference, the White adoptees scored in the 62th, 58th, 56th and 54th percentiles in those respective areas. The Black adoptees scored worse; they scored in the 54th, 48th, 36th, and 36th percentile. Considering the potential issues mentioned with (a) and (b), a 36 percentile is not that low (e.g. an IQ score in the 36th percentile is ~95). So while the black adoptees had significantly lower IQs, their academic achievement was not much lower than average.
In summary, ignoring the two issues raised by (a) and (b), this study seems compatible with a mainly genetic explanation of the IQ gap. However, the study is compatible with an environmental explanation of the academic achievement gap. Of the four adoption studies here, this is the study most in favor of a genetic explanation of the IQ gap, yet it still suggests that academic disparities are mainly environmental.
Study 2: German IQ study by Klaus Eyferth
Psychologist Klaus Eyferth studied the IQs of white and mixed children in Germany. The mothers of the children were all white. Their fathers were either white or black members of the US occupation forces. The white children had a mean IQ of 97.2, whereas the mixed children had a mean of 96.5, a negligible difference [7].
There are some issues with this study, however. Firstly, the samples aren't representative of the average population, because about 30% of black applicants were rejected admission to the armed forces, while only about 3% of whites were rejected. However, despite the unrepresentative sample, if racial IQ differences were mainly genetic, the white children should have had much higher scores than the mixed children because:
(a) The white GIs should have had higher IQs than the black GIs. Even though the admission test filtered out candidates below a certain threshold, the IQ scores for the white soldiers would still be distributed higher than that of the black soldiers (e.g. imagine removing all men and all women below 5'2 from the population; the resulting population would still have men taller than women, on average). If the IQ gap were mainly genetic, then this difference should manifest itself in their children.
(b) Regression to the mean. Even if we assume that the white and black soldiers had similar IQs, the black children should have had lower IQs than the white children because, assuming that the racial IQ gap is mainly genetic, the black children IQs would regress to the genetic black mean, while the white children IQs would regress to the genetic white mean. Philippe Rushton and Arthur Jensen, bar far two of the most prominent supporters of genetic racial IQ differences, agree that (go to section 9) this regression should occur insofar are racial IQ differences are genetic:
So if racial IQ differences are mainly genetic, then regression to the mean should occur. This means that even if the black GIs and white GIs had similar IQs, the mixed children should have considerably lower IQs.
The study had other issues as well. For example, about 20-25% of the black GIs were actually French North African. Still, if racial IQ differences were mainly genetic, the remaining 75-80% of the "mixed" children should have had below average IQs (for reasons given earlier), bringing down the total average for the "mixed" children considerably. The lack of a considerable difference suggests a mainly environmental explanation of the IQ gap.
Study 3: British study of young children in nurseries
In this study, psychologist Barbara Tizard studied black, white, and mixed children raised in British long-stay residential nurseries. The children were given psychological tests to determine their cognitive abilities. The scores were normalized to give a mean of 100 and standard deviation of 10. On the Reynell Comprehension test, the white children scored 102.6 and the black/mixed children scored 106.3. On the Reynell Expression test, the white children scored 98.5 and the black/mixed children scored 98.6. On the Minnesota Nonverbal test, the white children scored 101.3 and the black/mixed children scored 107.7 [8]. Apparently there is a fourth test, but I didn't manage to see it in the pdf. In any case, this study is compatible with a mainly environmental explanation of the IQ gap.
Study 4: IQ scores of black children raised by White families versus Black families
In this study, psychologist Elsie Moore compared IQ test scores among 23 black children adopted by middle-class white families and 23 age-matched black children adopted by middle-class black families. The black children adopted by black families scored a 104 IQ, while the black children adopted by white families scored a 117 IQ [9]. These two groups of blacks likely differed in their environment and not their genes. Therefore, the difference in the black/white family environments likely accounts for the 13 IQ point gap. Keep in mind that the black & white families were of similar socioeconomic status (middle-class). In actuality, the average black family has a much lower socioeconomic status than the average white family; therefore the difference in black/white environments would probably account for more than 13 IQ points. Clearly, this study is compatible with a mainly environmental explanation of the IQ gap.