MCPs, pause for a while. Women could be biologically superior to you, stronger in some ways.
A new study shows that women ó and only women ó have spines that are specifically adapted to carrying the weight of a fetus out front.
Liza Shapiro is one of the study's authors and an anthropologist at the University of Texas at Austin. Shapiro says a woman's body has had to solve a physics problem.
"It's just like when you're trying to carry a large box in front of you. The weight of the box is trying to pull you forward," she said. "So in order to offset that weight you have to ... contract your back muscles to push your spine the other way."
Ordinarily, this would put a huge strain on the muscles in your back. But when Shapiro and two other researchers studied 19 pregnant women, they discovered this isn't the case.
Shapiro says she and her colleagues realized women are able to carry most of their baby weight on their backbone.
Early in pregnancy, she says, a woman's spine has just a hint of an "S" shape.
"Throughout the pregnancy, as the fetus gets bigger and bigger, women are actively extending their spine, moving their upper body backwards, and increasing the curve of the lower spine," she said.
The lower bend in the "S" shape becomes much more pronounced. This allows bone to support much of the weight that would otherwise be carried by back muscles.
Shapiro says it is all possible because a woman's lower back has vertebrae shaped like wedges. And these vertebrae act like the wedge-shaped bricks or stones that architects use to create arches.
Katherine Whitcome, an anthropologist at Harvard, is the study's lead author. She says women have more of these special vertebrae than men do.
"A female has to grow a baby," she said. "The biomechanics of this growing baby, the increasing mass, challenge a female in a way that a male is never challenged."
So in the course of evolution, women's bodies have adapted.
Expectant mothers do get backaches. But they can still do all the things that allow them and their offspring to survive.
Whitcome says a man's spine could temporarily assume the same shape as a pregnant woman's.
But not for nine months.
"It doesn't cause instant failure," she said. "But you can imagine with this long and extended loading that the vertebrae would be subject to fracture and sustain various injuries."
The new study appears in this week's issue of the journal Nature.