London, Dec 13 (UNI) A new study can now reason every graceful and flexible step of Madhuri Dixit to a slightly stiff and awkward dance movement of Kunal Kapoor.
New findings have suggested that women have a stronger, supple and more bendy lower back than males.
The differences evolved millions of years ago to let expecting mothers stay mobile during pregnancy without the weight of a baby causing them to topple over.
The study comprised the backbones of modern women, two-million-year-old human fossils and chimpanzees- our closest relatives in the wild.
The extra weight during pregnancy shifts a woman's centre of gravity far in front of her hips and makes it much harder to stay upright, which is why she needs a bendy back.
''The body must change in dramatic ways to accommodate the baby and these changes affect a woman's stability and posture. It turns out that the enhanced curvature and reinforcement of the lower spine are key to maintaining normal activities during pregnancy,'' researcher Katherine Whitcome of Harvard University observed.
The study, published in journal Nature, found that when standing, expecting mothers leaned back and increased the curvature of the spine by 60 per cent.
That brought the centre of gravity back above their hips.
The extra bendiness was possible because the curvature took place in the lower spine, or lumbar region, over three vertebrae in women - compared with only two in men. The female joints were also larger and flared out further down the spine than those of men - improving their spine's strength.
The differences in the lower back were not just useful for pregnancy but also helped women to carry babies in their arms.
The study found similar differences in the spines of our ancient ancestors living at least two million years ago.
Early women lived very strenuous active lives and were forced to cope with the discomfort of childbearing while searching for food and escaping predators.
This helped early women to remain more mobile during pregnancy, which would have been essential to survival, and appears to have been favoured by natural selection, the study suggested.