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Perdita Stevens and her colleagues (Letters, É«ºÐÖ±²¥S, December 1) query my statement that mathematical ability is gender-linked.

There are many sources of data on the distribution of mathematical ability. The figure I gave is from one of the most extensive, the Study of Mathematically Precocious Youth, which each year since 1971 has identified many thousands of the most talented people. The proportions of boys and girls have changed little. I referred to the general population (of which half are women) because norms can be based only on that.

The sources of the variance are both genetic and environmental. It is possible there is discrimination against girls studying mathematics in Ireland; I have no evidence either way. Personally, I'd be surprised if any teacher of mathematics at any level anywhere, finding an able girl, did not do their utmost to encourage her.

It is true that somewhat different abilities are required for school work and research. But this applies equally to boys and girls.

Girls can do mathematics, but there are more very good boys. As to variations between European countries, more women run marathons in some countries than in others. But if we were to compete against a unisex species from outer space, the human marathon team would be male.

John Radford
Emeritus professor of psychology University of East London