Hereditarianism III: Discussion

In the last post, we have seen that for African-Americans and Hispanics, IQ varies according to ancestry. In this post we will discuss what this actually means and whether there is still leeway for the environmentalist to wriggle about.

The key idea of this kind of admixture study is to show that the differences between ethnic groups can entirely be explained by genetic factors. This is done by showing that the IQ differences within each ethnic group by ancestry extrapolate to the differences between ethnic groups. So it is essential that we only look at IQ and ancestry within each ethnic group.

Without a strict restriction to one ethnic group, it would not be enough to prove that IQ correlates with admixture. We already know that there is an IQ gap and we already know that there is an “admixture gap”. So a correlation is already a given.

But what if the self-identified ethnicity is noisy? For example some of the “Hispanics” might actually identify or be identified as White. In that case the correlation between ethnicity and IQ would bleed over into the IQ-admixture. Of course this assumption borders on paranoia. But the correlations observed are quite small, which means that admixture explains very little of the IQ variance in the data set, which might seem counterintuitive from a hereditarian perspective.

So what kind of correlation should we expect? If the European-Amerindian-gap is 16 points, similar to the Hispanic standard deviation, shouldn’t we expect admixture to explain a very significant part of the variation? Well, actually not. If admixture is uniformly distributed the mean difference in admixture between two Hispanics is only 33.3%. This means the average IQ difference explained by admixture would at most be 5-6 points. But the admixture is not uniformly distributed, Hispanics with less than 40% European admixture are notably rarer. This is why the actual standard deviation of admixture is just 23.3. So we are down to less than 4 points explained by admixture. This would lead to a correlation of 0.50 … given perfect data. But both the admixture data and especially the IQ data invariably contain noise, reducing this correlation further. So it is actually not surprising that we only see correlations between 0.17 (for the very range-restricted African Americans) and 0.41 (for much more uniformly distributed African-European Hispanics).

A better way than looking at correlations to drive home the meaning of the hereditarian hypothesis is to visualize how mean IQ of percentiles change. The hereditarian hypothesis posits, that IQ varies continuously with admixture. This means that the IQ averages of admixture percentiles will more or less linearly increase.

To show this effect for each percentile would require a much larger data set. This data set is almost too small and heterogeneous to show the effect convincingly for quartiles. For example, as we have seen, the Hispanic IQ is slightly depressed compared to the same admixture in African Americans. Because the middle region of European admixture is dominated by Hispanics this results in a depressed middle if we use the whole sample.

Instead we restrict ourselves to the Hispanic sample. Because the mean White and mean Asian IQ in our data is almost identical, we can just pool European and East Asian admixture to create a well-powered Hispanic quartile admixture plot:

n=323, slope=21.56, intercept=75.32, correlation=0.273, p-value=6.217e-07

Here, we see that the average IQ of the admixture quartiles fall pretty nicely on the regression line.
This plot perfectly illustrates the hereditarian hypothesis: The averages vary exactly according to admixture. (Note also, that if we plot a line through the first two quartile averages only, we would overshoot the mean white IQ, presumably because the lowest quartile is slightly environmentally depressed. This might be happening in the African-American sample.)

It is tough to come up with environmental causes for IQ differences that vary according to ancestry. Colorism is one of the best tries. Colorism is the idea that racism is graded by how dark somebodies skin is, which varies according to ancestry, and that this racism somehow reduces IQ. Except when you are NE-Asian … Colorism as the reason for IQ varying with ancestry, is a theory that has a lot to prove before it can be remotely taken seriously.

However, IQ varying by ancestry also doesn’t prove that the gap is fully genetic. Or, to put it differently, even if we could predict IQ perfectly directly from the genome, it remains theoretically possible that there are gene-environment feedback mechanisms involved that allow us to reduce the magnitude of the gap by improving living/learning conditions. Of course the history of intervention studies tells us not to hold our breath.

So, what are the take-aways from this series:

  1. IQ varies by ancestry within ethnic groups with the same country of birth.
  2. This intra-ethnic variation fully explains IQ differences between ethnic groups.
  3. This invalidates most environmental explanations for the IQ gaps.
  4. And strongly suggests a genetic reason for IQ gaps between ethnic groups.
  5. Ancestry nonetheless explains little individual IQ variation – people should be judged as individuals.

Hereditarianism II: Admixture Data and Gaps

In the last post, we have seen, that the environmentalist position about group differences in IQ is mostly based on the idea of x-factors. Factors hard to identify that vary systematically between groups and affect IQ. Given that there are many factors that vary between ethnic groups, this is a difficult theory to disprove.

However, from a hereditarian perspective, two persons belonging to the same ethnic group can sometimes be differentiated by different amounts of a certain genetic ancestry. So in ethnic groups whose members have varying degrees of admixture of some original founding populations we can put the hereditarian hypothesis to the test. This is the case for African-Americans, who have varying degrees of European ancestry and for Hispanics, who are mostly a mixture of Europeans, Amerindians and Africans.

The hereditarian hypothesis predicts that IQ will vary within these groups with the amount of admixture for any chosen ancestral group. This type of admixture study has the power to rule out the majority of x-factors that systematically vary between ethnic groups, except for those that vary roughly according to ancestry.

A recent paper showed IQ varying by ancestry for Hispanics and African Americans [1]. These are the key figures.

The regression line of the relationship between cognitive ability and European ancestry in African Americans
And the same thing for Hispanics …

In this post we are going to reanalyze the underlying data set. This data set contains IQ scores for a couple of hundred self-identified Whites, Blacks, Hispanics, East Asians + other minorities and the percentage of their genome being European, African, Amerindian, Asian etc.

First we translate the cognitive ability measure, here given in whole sample standard deviations above the sample mean, into IQ, with white mean = 100 and white standard deviation = 15.

n=137, slope=23.283, intercept=79.6, correlation=0.176, p-value=0.0392

The slope of 23.283 immediately gives us the gap between 100% European and 100% African, while the intercept provides us with the IQ of a 100% African African-American. The regression line overshoots the mean white IQ. This might be noise, or legitimately smarter white genes in the black population, or Amerindian admixture in the whites reducing the mean, or a slight environmental downward bent of the left part of the plot. But whether we take the estimated gap, or the difference between actual white mean IQ and the 100% African IQ, the result is always strikingly close to Galton’s estimate.

Of course this is just a very small sample. With a very restricted range. However, we can immediately replicate this regression line with those Hispanics that have predominately African and European admixture.

n=79, slope=23.837, intercept=73.33, correlation=0.416475096463478, p-value=0.000134

This gives us a virtually identical gap. But the whole line is shifted down. This vibes well with other results, see for example [2]. The average Hispanic IQ in this sample is only 89.5, compared to a usual US Hispanic IQ of 92-93, so it might still be missing a few points of Flynn effect. Note, however, that this seems to affect the entire IQ range in the same fashion.

The combined sample of African Americans and Euro-African Hispanics of course also validates Galton’s estimate of the gap almost perfectly.

n=257, slope=22.282, intercept=77.979, correlation=0.401 p-value=2.34e-11

For comparison, for Hispanics with predominantly European and Amerindian the admixture plot looks like this.

n=323, slope=16.65, intercept=80.024, correlation=0.233, p-value=2.231e-05

The gap is some 7 points smaller and the percentage of European admixture is generally quite high, which is why despite the missing Flynn effect points, the average Hispanic IQ is 89.5 vs 83.7 for African Americans.

[1] Biogeographic Ancestry, Cognitive Ability and Socioeconomic Outcomes

[2] A study of intelligence of children in Brazil

Hereditarianism I: Galton and Gaps

Hereditarianism is the idea that differences in abilities and character traits are substantially genetic in origin. This has been largely validated for individual differences, especially when it comes to IQ.

Everything is heritable. [1]

“Hereditary genius” by Francis Galton published 1869 can be seen as the founding document of hereditarianism [2]. In “Hereditary genius” Galton observes that human traits are often normally distributed, including intellectual abilities. He then proposes a method to sort people into different grades of “eminence”. The grades A, B, C, D, E, F, G, and X are above the average, getting ever more illustrious and the grades a, b, c, d, e, f, g, and x classify people below average in lifetime achievement. He gives precise frequencies for each grade, so that it is possible to translate his statements into the language of IQ. Although Galton’s “eminence” is based on more than just intelligence (he mentions “zeal” and “working capacity”) it is probably the most important aspect.

His grades correspond to the following IQs:

A >100.0
B >110.39
C >120.88
D >131.33
E >141.78
F >152.24
G >162.60
X >171.30

As we can see, each grade should roughly correspond to a range of 10.5 IQ points.

Using his grading system he then starts to analyse the pedigrees of English judges and other notable men. He finds that “eminence” runs in families, and rules out a decisive role of nuture by looking at the adopted sons of popes.

He finally goes on to assess the difference between Africans and Europeans, in essence relying on several observations of tail effects. He diagnoses an average intellectual ability gap of 2 grades, which would translate to 21 IQ points.

First, the negro race has occasionally, but very rarely, produced such men as Toussaint l’Ouverture, who are of our class F; that is to say, its X, or its total classes above G, appear to correspond with our F, showing a difference of not less than two grades between the black and white races, and it may be more.

Hereditary Genius

To Galton group differences are obviously innate, but he does see moderating environmental influences. On the Africans in Africa he says:

Thirdly, we may compare, but with much caution, the relative position of negroes in their native country with that of the travellers who visit them. … [A]n average actual difference of three grades, of which one may be due to the relative demerits of native education, and the remaining two to a difference in natural gifts.

Hereditary Genius

However, the currently existing results about the heritability of IQ differences between individuals do not automatically transfer to group differences. If there are systematic environmental differences between groups, in-group heritability could be high, but the between-group differences would be environmental. And of course there are many actual and potential systematic differences between groups. Enough, that as soon as hereditarians have disproven one potential environmental cause for group differences, two new ideas are lined up by the environmentalists. These potential causes include socio-economic status of the parents, lead exposure, number of words heard in early childhood, peer groups, stereotype threat, many aspects of education, prenatal and postnatal nutrition, breast feeding, systemic racism and many more.

Although there is no clear-cut argument for predominantly environmental IQ gaps between ethnic groups, the environmental position is the current consensus.

“Hereditary genius” is a great read, because, while his methods are pretty dodgy, Galton is basically some hundred years ahead of the curve. A true founder of the field. In the next post we are going to analyze a data set to see how well Galton’s assessment of group differences holds up or whether the current environmentalist consensus is still in decent shape.

[1] Genetic influence on human psychological traits

[2] Hereditary Genius