The key to attractiveness?

Dr Devendra Singh scoured references to fictional beauties from modern times back to early Indian literature.

He found that slimness was the most common term of praise from an author.

The study, published in a Royal Society journal, adds to evidence highlighting the role of the ratio between waist and hips in attracting a mate.

While female waist size is acknowledged as important in modern Western society and culture, it is not completely clear whether this has always been the case.

Some experts have suggested that at other points in history, men may have preferred larger waists.

The only remaining evidence is cultural, and Dr Singh, from the University of Texas, has spent years examining representations of women through history - in one study, he measured the waist-hip ratio of hundreds of statues from different eras.

Erotic poetry

In the most recent research, he looked at how 'attractive' women were depicted in literature, analysing more than 345,000 texts, mainly from the 16th to 18th centuries.

While most of the writings were British and American, there was a small selection of Indian and Chinese romantic and erotic poetry dating from the 1st to the 6th century of the Christian era.

The finding that the writers describe a small waist as beautiful suggests instead that this body part - a known marker of health and fertility - is a core feature of feminine beauty that transcends ethnic differences and cultures

Dr Devendra Singh

University of Texas

While the most-often mentioned feature was the breasts, waistlines were mentioned 66 times, with a slim waist predominantly linked to attractiveness.

There was trend for slightly larger women in the 17th and 18th centuries - a trend typified by the paintings of Rubens - but demand for a slimmer waist was generally constant throughout the centuries.

Dr Singh said: "The common historical assumption in the social sciences has been that the standards of beauty are arbitrary, solely culturally determined and in the eye of the beholder.

"The finding that the writers describe a small waist as beautiful suggests instead that this body part - a known marker of health and fertility - is a core feature of feminine beauty that transcends ethnic differences and cultures."

Fertility test

Other studies have found a link between a woman's waist to hip ratio and her fertility, offering some explanation as to why, alongside breasts, waist size is viewed as important by men selecting a mate.

Levels of the female sex hormone oestrogen around puberty are thought to be important in setting a woman's body shape into adulthood.

Dr Piers Cornelissen, a psychologist at York University, has carried out his own experiments designed to test the theory.

He says that the sexual attractiveness of the curve between slim waist and hips may be due to a liking for well-fed women rather than a subtle sign of fertility.

His work uses mathematical equations to separate the amount of the 'curve' between waist and hip which is due to simple fat deposition, and that due to other factors such as bone structure and the effects of sex hormones.

He said: "When we break apart that 'curviness', it is almost impossible to find an effect for waist-hip ratio that is independent of effects such as body fat percentage."