LETTERS: Genes are only half the story

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POLLY Toynbee's article on genes and selection, ("Blame the genes of the poor, and pull up the middle-class drawbridge", 17 December), illustrates the odd preference of the media to choose people with little knowledge to discuss complex scientific issues in psychology and sociology, particularly with reference to intelligence.

Her appeal is to emotion, not to facts; and her notion that I invented the IQ is sufficient evidence of her lack of knowledge in this field - the IQ was invented five years before I was born! She throws doubt on one of the most established facts in psychology - that IQ scores are strongly determined by genetic factors, to the extent of some 70-80 per cent for adults in our type of culture - without apparently being familiar with the large experimental literature on this topic.

Apart from twin and adoption studies, these experiments demonstrate a strong regression to the mean effect, as expected in any physical or mental trait that is inherited less than 100 per cent. This effect means that children of very dull parents are dull - but less so than their parents - while children of very bright parents are bright, but less so than their parents. In both cases, the children regress to the mean of the population. Children of average bright parents are mainly average, but some are bright or very bright, others dull or very dull. This variability contradicts Toynbee's notion of genetics producing a kind of caste system; quite the opposite.

It is responsible for the great mobility in our class system; in an analysis of social class in America, using five steps (higher white collar, lower white collar, higher manual, lower manual, and farm worker), only 31 per cent of children were in the same class as their parents. Of children in class four, 21 per cent rose to class one, 12 per cent to class two, 23 per cent to class three; only 30 per cent stayed in four!

HJ Eysenck PhD DSc

Professor Emeritus of Psychology, University of London