Wide hips are not a detriment to a woman’s gait. They are adaptive. They also affect how many women walk. Having wider hips causes more rotation, or swivel, when walking. This allows women, who typically have shorter legs than men, to take longer strides than one might expect. Wider hips don’t make a woman’s walk less efficient. They make it mechanically different.
Especially in endurance athletics, the gap between men and women is closing. Some studies show that women’s leg muscles tend to be more resistant to fatigue than men’s. In sports that test endurance rather than strength and speed, women may have an advantage.
The wrongheaded notion that female walking is compromised remains pervasive. It has been called the hangover from Genesis. Walking is related to both thinking and freedom, and historically, men have thought women “deserve less of each.” In a culture that interpretations of the book of Genesis have heavily influenced, the obstetrical dilemma may be a flawed hypothesis, but difficult labour, dangerous childbirth, and helpless babies are not Eve’s fault, but evolution’s. What happens to a woman’s gait and posture during pregnancy? As gestation reaches the third trimester, a sizable amount of baby, placenta and amniotic fluid accumulates in the front of the body, pulling the center of mass forward.
Quadrupedal animals don’t have the same problem since weight gain during pregnancy wouldn’t alter the center of mass. Why don’t women tip over? The answer lies in the small of the lower back. Men and women both have five lumbar vertebrae. In men, the bottom two are shaped like wedges, producing a curve in the spine that brings the torso over the hips. But, in women, the bottom three vertebrae are wedge-shaped, giving them a larger curve. This helps women get the shifting center of mass back over the hip joints, keeping them balanced as they walk. This sex difference in the shape of the third-to-last lumbar vertebrae occurred early in our evolutionary past. Australopithecus had it over two million years ago.
Women and Pregnancy
It has been shown that women walk as efficiently as men. But in some circumstances, they are even better at it. We don’t walk only in straight lines or on flat surfaces, and neither did our early ancestors. We don’t always walk empty-handed, either, and neither did they. With hands freed by bipedal walking, they carried food, water, tools, and babies. Walking while holding an object roughly the same size as a human infant can increase the amount of energy expended by nearly 20%. But the energy required is significantly reduced in individuals with wide hips from side to side – the kind often found in women. Women are, by all measures, better carriers than men. Wide hips are not about childbearing; they are about child carrying.
When waking, humans can settle at their most efficient pace and walk great distances without using too much energy. But walking with a group, especially one that includes children, often means slowing down, stopping, and speeding back up. When men vary speeds, they use more energy. Wider hips make it easier for women.
Women use their hips as a shelf, perching babies there, and they walk around the house. When men try it, the babies slide down their thighs. With no bony shelf, men’s arms tire. Carrying squirming kids is not easy, never mind if you are walking six miles a day as modern hunters and gatherers do.
