Martin Yuille and Jonathan Bard (Letters, 9 March) assert that recent scientific developments have undermined genetic determinism, the idea (in Yuille’s words) that human traits “specify the characteristics – in their entirety – of the individual”. This overlooks the fact that geneticists have known for 100 years that variation in most traits of biological importance reflects the combined effects of many genes with individually small effects, together with non-genetic factors that include direct effects of the external and maternal environments on the individual.
This year geneticists will celebrate the centennial of Sir Ronald Fisher’s classic paper laying the foundations for the statistical analysis of such joint effects. These concepts and their evidential base have been explained in many subsequent scientific papers, and in genetics textbooks. For example, p27 of Human Heredity by J V Neel and W J Schull (published in 1954, and the standard textbook of human genetics for many years) explains, in a chapter entitled Nature and Nurture, “When we speak of the effect of any particular gene, this is really an abbreviated way of referring to the result of the introduction of a particular gene into a particular genetic background and particular environment. Genes do not operate in a vacuum, but, rather, each has its role to play in the complex machinery of development.” Genetic determinism is not a concept used by practising geneticists.
Brian Charlesworth and Deborah Charlesworth
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh
• Martin Yuille accurately defined genetic determinism, by which definition Jensen and Eysenck, now conveniently dead, were certainly not genetic determinists as alleged by Steven Rose. Recirculating these false facts only adds ammunition to rightwing activists when they point out that anti-racists have their heads in the sand. It is hardly news to propose that there might be between-family as well as within-family genetic influences on intelligence.
Anthony Gordon
London
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