Bottom line on perfection

It is slightly plump, rounded, and a clear sign of fertility and general health.

According to Britain's leading bottom boffins, this is the perfect female rear, and for celebrities such as Kylie and J-Lo, success has rested on the scientific behind.

The key is the waist-to-hip ratio. For the perfect British bottom, apparently personified by Kylie, the ratio should be exactly 0.7.

However, the research also revealed perfection is a fleeting thing - trends change over time, and vary between countries. Those with larger behinds, for instance, should head to Africa, where they are seen as a sign of wealth.

The new research is revealed in a documentary, The Bottom Line, being shown on the Discovery Health channel on 3 December.

Professor John Manning of the University of Central Lancashire, who carried out the study, said: "The bottom is, on one level, very simple - it's just muscle and fat. However, the bottom is a general sign of a woman's hormonal state, and her general health.

"Fat is the key. In women it is stored in the bottom and forms a reserve that allows them to get through pregnancy. It's not really surprising therefore that men find those with a rounded bottom more attractive - it's a clear sign of their ability to reproduce."

Psychologist Dr Linda Papadopolous believes that, in the UK, Kylie has the perfect rear. "What British men want is something relatively small and pert. What you see in Kylie is also an ageless bottom - it could still be mistaken for a 14-year-old's."

But, Dr Papadopolous warned, tastes do change. "J-Lo, for instance, is probably now just too big for current tastes," she said. "But men will always be absolutely fascinated by women's bottoms - evolution has programmed them."