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The letter from Gijsbert Stoet ("Rewarding equality", 1 September) points out that gender ratios in academia may simply reflect different choices made by women and men, who tend to be influenced differently by hormone levels that in turn are influenced by genetic inheritance.

The nature-nurture debate is not new and need not be restricted to gender issues, but it remains important so long as there are calls to impose gender (or class or ethnic) ratios, as reported recently in several issues of Times ÖйúAƬ. Predictably, Stoet's letter has not provoked a rebuttal from those who would explain anomalous "ratios" entirely in environmental terms. It appears that sociologists prefer to ignore human biology rather than engage with it, but this need not be the case.

In medical research, data comparing identical and non-identical twins are often used to disentangle genetic and environmental influences. For example, in my own field of research, twin studies show that intervertebral disc degeneration is 35-75 per cent inherited: the exact percentage depends on definitions and on the population investigated, but the importance of such studies is that no medical scientist (or medico-legal lawyer) can now blame bad backs entirely on environmental factors. Yet in the social arena, "bad ratios" are conventionally blamed entirely on human unfairness or ignorance, even though the origins of these ratios are largely unknown, and even though mental characteristics are known to be inherited along with physical ones.

Sociologists presumably concentrate on environmental influences because that is where their interests lie, but can any research be valid if it ignores a potentially large influence on the problem being studied? More particularly, should raw data concerning gender/class/ethnic ratios ever be used to inform social policy before the ratios have been properly explained?

Mike Adams, Department of anatomy, University of Bristol