The beauties of Rubens could have been sent to the Association of Anonymous Obese. And even Marylin Monroe would be a Miss Piggy compared to current fashion models.

But regardless of race, culture and time, a relatively slim waist is that part of the woman body which has triggered the most and continuous interest in males. Clearly, plump women were preferred by Europeans over slim ones in the past centuries, but what was constant was the relative narrowness of the waist.

A slim waist was always admired, through time and cultures, from the Chinese sixth dynasty palace poetry (from the fourth to the sixth century AD) and to the ancient Indian epics, the Mahabharata and the Ramayana, from the first to third century AD, and English poems of the 16th century.

Scientists believe that a narrow waist is unwittingly seen as a sign of strong health and fertility. Abdominal obesity has been connected to low levels of estrogen, low fecundity and increased risk of fatal diseases (like diabetes and heart disease) and inflammation. A new theory finds a supplementary explanation for the hourglass figure and its irresistible attractiveness for men. "Shapely hips and thighs hold essential nutrients that nurse brains and could produce smart kids too," said Steven Gaulin of the University of California at Santa Barbara and William Lassek of the University of Pittsburgh. "Men respond because it's reproductively important," Lassek said at a meeting of the Human Behavior and Evolution Society.

This team believes that women with low waist-to-hip ratios (WHR) deliver offspring with increased cognitive abilities than less curvy mothers do. The answer could be encountered in omega-3 fatty acids, stored in the hips and thighs and which make a large percentage of the human brain. This type of fatty acids is stored by the female body below the waist with the installation of the puberty.

The body accumulates these essential molecules preparing the woman's body for the third trimester of an eventual pregnancy, when the fetal brain is rapidly growing. Fats accumulated in this area will be mobilized until the child stops breast-feeding. Of course, consuming omega-3 fatty acids during the pregnancy and breastfeeding helps, but the body best uses its own deposits. During our early evolution, when food was not so available, these fat deposits could have been essential in reproduction.