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December 11, 2003

IQ and the Wealth of Nations

In a series of recent posts - A, B, C and D - I questioned whether differences in IQ between nations necessarily had a genetic basis. Dienekes also has some excellent posts on the subject (November 28 onwards).

I promised not to return to the subject. I am now breaking that promise, but there are extenuating circumstances.

In comments on my last post, it was claimed that I was wasting everyone’s time by discussing the subject without first reading the book IQ and the Wealth of Nations (Praeger, 2002), by Richard Lynn and Tatu Vanhanen, because (a) I shouldn’t write long criticisms of the book without reading it, and (b) the book already contained answers to all the points I was making.

Objection (a) is wide of the mark, as my posts didn’t even mention the book, as distinct from the data on Richard Lynn’s website. But I took objection (b) to heart. I would hate to waste people’s time, not least my own. And if the book does answer my concerns, I would like to know how.

Unfortunately the book is not easily available in the UK, but a reader alerted me to a reference library copy (thanks, Nigel), so last week I trekked off to the library, placed my request, and waited anxiously for the book to emerge from the bowels of the library (possibly an apt metaphor).

What new evidence would there be? What devastating answers would I find to the points I had raised?

And the answer is.....

Zero. Zilch. Zip. Nada. Diddly-squat.

The book takes no firm position on the extent to which the IQ differences between nations are genetically based.

This is not to say that there is no mention of the subject. An early section covers ‘The Heritability of Intelligence’. This describes three methods of estimating heritability (MZA, MZ/DZ, and adoptive-parent/offspring), and concludes (page 25): “We have seen in this section that the three methods for estimating the heritability of intelligence yield closely similar conclusions and that the figure is around .80 or 80 percent. [DB: this is rather high, but I won’t go into that now]. The precise magnitude of the heritability of intelligence does not matter for the purposes of the arguments developed in this book. The significance of the high heritability of intelligence is that it implies that the differences in intelligence between the peoples of different nations are likely to have a genetic basis”.

The unsophisticated reader might take this as meaning that 80 percent of all the individual differences in IQ across the world have a genetic basis, or perhaps that 80 percent of the differences in mean IQ between nations are likely to be genetic. Of course, it means nothing of the kind. Strictly speaking, an estimate of heritability within one population implies nothing whatever about the heritability within any other (non-overlapping) population, still less about the differences between populations. Heritability of 100 percent within a population would be quite compatible with heritability of zero between populations. The most one can legitimately say is that if the genetic and environmental differences between populations are of the same kind as the differences within them, then a high heritability of IQ within populations somewhat increases the probability that the IQ differences between them are partly genetic. (‘Probability’ is used here in a loose, non-quantitative sense equivalent to ‘plausibility’.) The actual amount of any genetic influence would need to be investigated in each case. Presumably L & V would agree with all this, as it is standard genetic doctrine. It is a pity that they do not explain it more clearly for the benefit of their (direct and indirect) readers, some of whom may be very unsophisticated indeed.

L & V return to the subject towards the end of the book. In a section headed ‘Genetic basis of national differences in intelligence’ they say (page 193) “We believe that national differences in intelligence have a substantial genetic basis. Differences in national IQs have evolved over many thousands of years as a result of adaptations of human populations to local geographical and climatic conditions. We do not know to what extent differences in national IQs are genetically determined, but it is quite probable that they are at least partly genetic... [italics added] It is improbable that the genetic components of intelligence would have remained the same in all populations through tens of thousands of years, when so many other characteristics of the populations vary as a consequence of natural selection”. So far so good. I said much the same in my post B. The only point I would take issue with is the word ‘substantial’, which implies a claim about the relative size of genetic effects that needs to be demonstrated. The only direct evidence L & V offer on this point is a casual, undocumented, and oversimplified assertion about the effects of trans-racial adoption.

But in any event, L & V do not claim that differences in national IQ are wholly genetic. In a section on ‘Nutrition’ , they say (page 184-7): “No general consensus exists on what the environmental factors are that determine intelligence... We believe there is strong evidence that one of the major biological factors affecting intelligence is the nutritional quality of the diets of pregnant women, and the nutrition obtained by the fetus, and by babies, young children and adolescents; this affects the growth of the brain, which in turn, affects intelligence... the secular [i.e. long-term] rises in intelligence that occurred in Western populations during the twentieth century are largely attributable to improvements in nutrition... There were substantial improvements in the quality of nutrition of the populations of the western nations during the twentieth century that were responsible for increases in average height of about one standard deviation. The increases in intelligence have been of about the same order... There is little doubt that the extensive poor quality of nutrition in economically underdeveloped countries has an adverse effect on the intelligence of the populations... There is a growing consensus among experts in this field that poor nutrition is a significant factor responsible for low intelligence in poor countries.”

This is a substantial concession to the effects of environment. (See also the section on ‘Positive Feedback Effects’, p. 56.) If it is admitted that both genes and environment affect the differences in national IQs, then the question is how much, not whether, each contributes. L & V implicitly recognise that at least one standard deviation of difference in IQ may be due to environmental differences between populations. One standard deviation of IQ is 15 IQ points. The total cumulative increase in IQ scores (the Flynn Effect) has probably been rather more (I may post separately on this subject). Lynn has elsewhere recognised this, but claimed that part of the observed increase in scores is ‘spurious’: “The IQ gains on the Wechsler tests, amounting to approximately 3 IQ points per decade, should be regarded as genuine increases of intelligence, but the larger gains obtained by 18-year-old military conscripts on the Raven Progressive Matrices... are largely spurious. They are best interpreted as schooling effects.” (Lynn in U. Neisser (ed.), The Rising Curve, 1998, p. 212. Cf. L & V’s comments on schooling effects at pp. 188-9 of their book.)

Be that as it may, the cumulative increase in observed IQ scores, due to environmental differences of some kind, has in some cases been over 20 points. But most of the IQ differences between nations fall within a range of 20 IQ points, and therefore within the potential scope of environmenal influence. While part of these differences may have a genetic basis, we cannot determine, merely from the IQ data themselves, the size or even (in some cases) the direction, of any genetic differences. For example, L & V give the mean IQ of India as 81, and of the USA as 98 (against a UK mean of 100). But, even assuming that the IQ data are technically sound, we cannot say, from the data alone, whether in environments of equal quality the IQ of Indians would be lower than, equal to, or higher than that of Americans. In fact, the educational and economic performance of Indian migrants to the UK and the USA suggests that their ‘genetic’ IQ is relatively high. This could perhaps be accounted for by selective migration, but this is a hypothesis to be tested, not a mantra to be chanted.

The comments above are not intended as a comprehensive review of L & V’s book. L & V’s main purpose is not to argue about nature and nurture, but to demonstrate a correlation between IQ and economic performance. I think they are successful in doing this (I could quibble about many details, but won’t do that here). It is an important issue, and they deserve credit for raising it.

Posted by David B at 08:06 AM