IT’S a question that has baffled scientists for years: why are women so much curvier, particularly in the buttocks and thighs?

The answer: it’s all about babies’ brains.

Researchers have found that the development of babies’ brains relies on fat supplies stripped directly from the mother’s thighs and bottom, especially during breastfeeding.

They found that the quantity of such fat supplies may directly affect a child’s intelligence and chances of survival — which could also provide a clue as to why some men are evolutionarily hardwired to prefer curvier women.

According to Professor Will Lassek of the University of Pittsburg, the fats in women’s buttocks and thighs are high in a chemical called docosahexaenoic acid, or DHA.

“The fat in these areas is a depot for building a baby’s brain,” said Professor Lassek, who has published a number of science papers and a book on the subject, Why Women Need Fat.

“You need lots of fat to make a nervous system and the fats in these areas are also enriched in DHA, which is a particularly important component in the human brain. It looks as if women have evolved to accumulate these fats and hold on to them — until a baby arrives.”

Professor Lassek told the UK’s Sunday Times it has always been a “complete mystery” why women have so much fat. “Mammals’ and primates’ bodies typically have about 5-10 per cent of fat but in human women that rises to 30 per cent on average,” he said.

“This is similar to the levels seen in bears going into hibernation or whales living in cold Arctic seas. Women have traded muscle for fat so they are about a third as strong.”

According to Professor Lassek, around 80 per cent of the DHA needed for a baby’s brain comes from the mother’s stored fat. “Less than 1% of body fat is DHA so a lot of fat has to be shifted. That’s why lactating women may lose a pound of fat a month,” he told The Times.

David Bainbridge, a reproductive biologist at Cambridge University and author of the upcoming book Curvology: The Origins and Power of Female Body Shape, said there was evidence that women with larger thighs had higher levels of brain-building breastmilk lipids.

“There is even evidence that they and their children are more intelligent as a result,” he said, adding that such factors had affected the evolution of men, hardwiring them to prefer women with curvier figures because their stronger, brighter children would be more likely to survive.

As to why all women haven’t therefore evolved to look like Kim Kardashian, Dr Bainbridge suggested that although men may prefer curvier women, they may also choose other factors such as intelligence or personality.

“Perhaps men have spent the last few hundred thousand years sexually selecting mates for all sorts of different reasons, or maybe they are just inherently Catholic in their tastes,” he said.

“A detailed examination of male sexual desire may help us discover whether it really was men who have made women so beautiful — and diverse.”