a scientific zombie still going strong

ruthlessly enforced the upholding of the false dogma of acquired traits being encoded in the genetic material (with disastrous consequences for the Soviet agronomy).

The heritability of intelligence – a scientific zombie still going strong

In astronomy, today a scientific field based on physics, science eventually trumped ideology and today no one doubts the heliocentric view. But in science, where one might think that rational thought should finally prevail, things need not happen like that. And it did not happen in a field where, had science trumped prejudice, disastrous social and political consequences could have been avoided: the controversial issue about the heritability of intelligence. Here the opposite happened: prejudice not only trumped scientific reason in the past, but still does so today.

How could something like this happen in a debate deemed to be a scientific one? The treatment of the issue about the heritability of intelligence and other mental traits as it happened in science is one of the crassest and most depressing examples of nonscientific aspects being so dominant as to preclude a consensus about a genuinely scientific problem. More depressing still: the consensus could have been reached by some fundamental and rather simple considerations.

Ever since Francis Galton described the regression effect and mistook it for a law of heredity3 around the end of the 19th century, scientists have believed that intelligence is heritable to a substantial degree, somewhere between 50% and 80%. When quantitative genetics, the statistical tool for determining the heritability of quantitative traits, had been developed in the 1930s, psychologists applied it to intelligence and still do so today, against the warnings of one of the experts in the field, Douglas Scott Falconer4 (1989). They ended up with heritability estimates between 10% and 90%. They also ignored the warnings

3 Galton falsely derived heritability from parent-child regression while this regression is actually affected both by genetic and environmental factors. Regression is not a biological but a statistical law, applicable to all kinds of correlating variables. 4 Quantitative genetics was developed in order to predict breeding success in plants and animals. The preconditions for its use for human mental traits cannot be satisfied due to the lack of experimental control.

implied in these results; instead they simply took the average and proclaimed intelligence to be 50% heritable (Neisser et al., 1916). The warning: the large differences in heritability estimates between populations found cannot possibly be genetically caused in a genetically very homogeneous population like homo sapiens. A short look at the definition of heritability in quantitative genetics would have revealed that the differences must primarily be attributed to differences in environmental variation between the populations.5 As a consequence of all this, there simply cannot be a general value for the heritability of intelligence and, more importantly, a heritability coefficient practically cannot tell anything about the degree to which intelligence can be increased by social intervention (for a more detailed explication see Velden, 2014). And as a consequence of this, it makes little if any sense to do heritability estimates for intelligence.

Molecular genetic studies, which had for a long time been hoped to help clarify things, have not found any substantial contributions of heredity to intelligence.6 Yet still we are being bombarded by psychologists with proclamations of a high heritability of intelligence (e.g. Plomin, 2018). The evidence lacking, we are being told that it will show up in the future, a strategy which, as we will see, also characterizes the field which is the topic of this book, the attempts to create human-like computers.

As mentioned, research on the heritability of intelligence did not happen on a scientific playground but had huge social and political implications.The most disastrous of the effects of the belief in a high heritability of intelligence were the ones on immigration restrictions for certain countries, on compulsory sterilisation of people deemed feebleminded (a vague, unscientific “diagnosis”), and restrictions on access to higher education for students deemed not to be intellectually fit for it.

5 In the simplest case, which can be taken for explanatory purposes, the heritability coefficient (h2) is defined as , where Vg is the part of the total variation due to genetic differences, and Ve is the one due to environmental differences. Vg being constant in a genetically homogeneous population like homo sapiens, differences in h2 can only be explained by differences in Ve. 6 A huge (80000 children and adults) so-called genome-wide association study showed that at maximum 4.8% of the variance in intelligence may be explained by genetic differences (Editorial, 2017). h2 =

Vg Vg+ Ve