India has 37 million more men than women, partly because the preference for sons prompts sex-selective abortions and infanticide.

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However, because there is such a strong contrast in the preference for menthol by race and sex and because there are large differences in the rates of these cancers also by race and sex, we felt that this was a case in which an ecologic approach could be informative.

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The other reason specific to a few Asian societies is because a combination of traditional preference for sons and the availability of sex-selective abortion skewed the sex ratio at birth 20 years ago, leaving too few native-born women now.

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It also proves that a strong preference for sons over daughters - leading to sex selective abortions - is just part of the story.

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However, as Daniel Goodkind, based until recently at the University of Michigan, argues in a forthcoming paper, sex selection might well continue in China's small families, even if the son preference vanished, because most parents want a son and a daughter.

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But because they have not had the historical experience of a strong preference for sons, Ms Das Gupta suggests, they also seem less likely to push the sex ratio to the extremes that it reached in Punjab or China.

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Mr Singh's romantic life had become a casualty of India's preference for boy babies, which in his state, Haryana, has led to the most skewed sex ratio in India: 116 to 100, according to the 2001 census, compared with a national average of 108.

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