In this post I will document the relationship between racial ancestry and IQ while assessing its strength as evidence about the causes of racial IQ differences.
In America, there have been studies going back to the 1920’s which looked at the correlation between racial phenotypes like skin color, or nose width, and IQ, among African Americans. These studies have consistently produced modest positive correlations between proxies for white ancestry and IQ.
|Peterson and Lanier (1929)||83||Various||0.3|
|Peterson and Lanier (1929)||83||Skin Color||0.18|
|Peterson and Lanier (1929)||75||Various||0.05|
|Scarr et al. (1977)||144||Skin Color||0.155|
|Lynn (2002)||430||Skin Color||0.17|
|Hu et al. (2019)||1455||Skin Color||0.112|
|Fuerst et al. (2019)||637||Skin Color||0.21|
There have also been a large number of studies which group Blacks based on racial phenotype and then compare the test scores of Blacks in each group. The vast majority of this research has found that blacks with more European phenotypes, for instance lighter skinned blacks, have higher IQ scores than do Blacks with more African phenotypes.
|Citation||N||IQ Ranking||Supports Hereditarianism|
|Ferguson (1919)||657||Light > Dark||Yes|
|Ferguson (1919)||667||Light > Dark||Yes|
|Ferguson (1919)||334||Light > Dark||Yes|
|Peterson and Lanier (1929)||83||Light > Dark||Yes|
|Peterson and Lanier (1929)||83||Light > Dark||Yes|
|Young (1929)||277||Light > Dark||Yes|
|Tanser (1939)||54||Mixed > Non-Mixed||Yes|
|Tanser (1941)||204||Mixed > Non-Mixed||Yes|
|Codwell (1947)||480||Mixed > Non-Mixed||Yes|
|Bruce (1940)||72||Light > Dark||Yes|
|Davenport (1928)||200||Brown > Black||Yes|
|Klineberg (1928)||200||Less African > More African||Yes|
|Kock and Simmons (1926)||1,078||Light > Dark > Intermediate||Mixed|
|Grinder et al. (1964)||940||Light > Intermediate > Dark||Yes|
|Rowe et al. (2002)||13,966||White > Mixed > Black||Yes|
|Fuerst et al. (2019)||9,043||White > Mixed > Black||Yes|
Notably, Davenport (1928) and Grinder et al. (1964) both found that this was true even in Jamaica, a majority Black country. It is also worth noting that Codwell (1947) and Rowe et al. (2002) found this was true of American blacks even after controlling for economic class.
Hicks and Pellegrini (1966) analyzed studies published between 1921 and 1954, and found that skin color accounted for 6% of the variance in IQ between blacks.
There are two early studies worth mentioning which do not conform to these standardized methods. First, Strong (1913), as reported in Shuey (1966), found that rates of mental retardation were similar in dark and light skinned blacks in a sample of 122 African Americans. This study is hard to interpret because it looks at the far left tail of the IQ distribution rather than the mean. Whites have a larger standard deviation in IQ than do Blacks and so lighter skinned blacks may have a larger SD than do dark skinned blacks. This in turn would lead them to be over-represented among those at both extremes of the IQ distribution relative to dark skinned blacks. In any case, this is a single study and does little to change to weight of the totality of evidence in this literature.
The second study worth mentioning is Witty and Jenkins (1936). This study looked at the ancestry of 63 smart black kids (IQs > 120), as reported by their parents, and found that their degree of white ancestry was lesser than that of a national comparison group derived from Herkovits (1930). They also found that the smartest subset of this group (IQs > 140) did not have more white ancestry than the rest of the group.
As it turns out, the comparison group used by Witty and Jenkins was, itself, an elite sample of blacks that had higher than average white ancestry, so the whole design of this study is bunk (Chuck, 2008). In any case, it’s a single study with a sample size small enough that it, like Strong (1913), doesn’t do much to change the total weight of the evidence.
So, white ancestry, as proxied by phenotype, is correlated with IQ among American and Jamaican Blacks, and this remains true after controlling for socio-economic status. This was known by the 1950s, and two competing stories emerged to explain this data.
Some said that this is exactly what we would expect if the IQ difference between Blacks and whites was significantly caused by genes. Others said that these racial phenotypes correlate with the degree of discrimination experienced by blacks, and this discrimination is a significant cause of the black-white IQ gap.
A well known study along these lines is Scarr et al. (1977) who found that racial ancestry, as measured via blood analysis, did not correlate with IQ in a sample of 144 African Americans once socio-economic status and skin color were held constant.
However, this sample was small, and blood group analysis is a very crude measure of racial ancestry.
Turning to more recent research which has employed a modern genetic measure of racial ancestry, we see that there is an association between European admixture and IQ among African Americans.
The same was found to be true of Hispanics:
It’s also been shown that this association persists even after controlling for self identified race/ethnicity (SIRE) and parental socio-economic status.
Perhaps most importantly, it’s been shown that skin color does not correlate with IQ within sibling pairs of African Americans.
So, it is true that darker skinned African Americans score lower on IQ tests than lighter skinned African Americans, but it is not true that darker skinned siblings score lower on IQ tests than their lighter skinned siblings. This result is what a genetic model would predict, because while skin color is generally a correlate of over all European ancestry, within a pair of siblings it is not. Lighter skinned siblings are not whiter, on the whole, than their darker skinned siblings, they just happened to get more European admixture for the genes involved in skin color. This does not imply, however, that they got more European admixture across their entire genome. Their parents are the same and so, on average, these two siblings will be equally white despite their skin color difference.
By contrast, the discrimination model would predict that darker skinned siblings would have lower IQ scores since they would suffer more discrimination than their lighter skinned sibling.
More evidence against the discrimination model comes from studies on regional variation in IQ which have shown that the whiter the average person is in a given state or province, the higher the mean IQ of people in that region tends to be. This has been shown to be true in five separate American nations.
As noted earlier, the correlation between skin color and IQ has also been demonstrated multiple times at the individual level in Jamaica.
Classic racial phenotypes like skin color, skull size, and nasal index (the ratio of nose width to nose length) have also been shown to be strong correlates of national IQ variation. This is true even when only comparing African nations, or when comparing regions of Japan.
|Templer (2008)||Skin Color||129 Nations||-0.91|
|Kura (2013)||Skin Color||47 Japanese Prefectures||-0.42|
|Meisenberg and Woodley (2013)||Skin Color||143 Nations||-0.86|
|Meisenberg and Woodley (2013)||Cranial Capacity||143 Nations||0.77|
|Templer and Stephens (2014)||Nasal Index||128 Nations||-0.6|
|Templer and Stephens (2014)||Nasal Index||48 African Nations||-0.58|
|Templer and Stephens (2014)||Nasal Index||80 Eurasian Nations||-0.16|
Since many of these nations don’t have a white ruling class that is accused of racism against blacks and Hispanics, the most sensible way to interpret this data is to say that these phenotypes correlate with evolutionary pressures (e.g. climate) which have selected for intelligence. Thus, research on the relationship between racial ancestry and IQ lends support to the view that racial differences in intelligence are significantly caused by genetics.