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.
“Hereditary genius” by Francis Galton published 1869 can be seen as the founding document of hereditarianism . 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:
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.
 Hereditary Genius