Pregnant women do not tip over, and researchers say an evolutionary curve has a lot to do with the reason why.
Anthropologists have found that women’s lower vertebrae evolved in ways that reduce back pressure during pregnancy, when the mass of the abdomen grows by nearly one-third and the center of mass shifts forward considerably, reducing stability.
Women tend to deal with the shift — and avoid tumbling over like a bowling pin — by leaning back. But that puts even more pressure on the spine and muscles.
Researchers from Harvard University and the University of Texas report in the current issue of the journal Nature that evolution has produced a stronger and more flexible lower spine for women. After studying 19 pregnant subjects, they found that the lumbar, or lower back, curve in women extends across three vertebrae, as opposed to two in men. And the connecting points between vertebrae are relatively larger in women and shaped differently in ways that make the stack more stable and less prone to the bones shifting out of alignment or breaking.
