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In your leader (THES, March 15) relating to the extent to which our behaviour may be genetically controlled, you report that "there is no slick term for summing up these (genetic or environmental) interactions" (my italics).

There is a term however, and although it may not be a slick one, its simplicity reveals a powerful and important idea. I commend to you the concept of: p = g x e where p represents the phenotype, ie the totality of the way in which any organism presents to the outside world - in plants this would encompass height, leaf shape, flower colour etc, while in humans it summarises the way we look, think, behave and even believe; g represents the genotype of the organism, ie its total genetic capacity, inherited from its parents; e represents the (changing) environment(s) in which the organism completes its life history.

The idea is that the appearance and behaviour (in the broadest sense) of any organism will be a function of its genetic inheritance interacting with its environment. This presents us with a spectrum of possibilities. At one end are the phenotypic characteristics which are completely under genetic control, eye colour in humans, for example. At the other end are characteristics which develop entirely in response to environmental stimuli, such as the language(s) which we speak.

In between are many of the "contentious" characteristics - musicality, intelligence, a "tendency" to aggressive behaviour, or to homosexuality - about which the "genetics or environment" debate has raged. p = g x e shows us that the question "Is this characteristic under genetic or environmental control?", is not appropriate in this context.

If it were possible to increase the general awareness of this simple term (by inclusion in the national curriculum key stage 3 programme of study for science?), it would have a number of beneficial effects: it would make a small contribution to the public understanding of science; it would demolish the "nature versus nurture" debate; it would open up the productive study of the extent to which the environment, acting on our inherent genetic capacities, makes us all the phenotypes that we are.

Steve Farrow

Senior lecturer in primary education University of Durham