Genetic glitch

22nd June 2007 at 01:00
In his article "Why nurture wins every time" (TES magazine, June 15) Oliver James commits a basic but all too common error. While noting the questionable standing of twin studies, he says "they demonstrate that great swathes of our psychology come out only 10-30 per cent genetic". What he means by "genetic" is that traits "are down to our genes". But this is simply wrong.

The figures he quotes concern the heritability of a trait, where heritability refers to the proportion of the variance in a trait among individuals that is attributable to differences in their genes (more correctly, their genotypes).

Contrary to what he suggests, such figures do not tell us how much of a trait is due to genes and how much to the environment. To be fair, he does use the term "heritability", but not correctly. In fact, there is a long-standing consensus in biology that talk of the kind Mr James and many others use is meaningless.

Dr Terence Sullivan Ferry Lane primary school, London

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