TMLS: Gender Dimorphism in Hipbones

Another edition of Thank My Lucky Stars, where unnoticed things get appreciated!

I was at the gym when I noticed something. Do you ever wonder why women have a sway in their hips when they walk? It’s very charming, similar to how their deuce smell like roses. So why does the sway happen?

Simple: their hip bones are different. Observe the male to the left and the female to the right.

Notice that the male hipbone is more narrow and longer in the vertical direction. In contrast the female hipbone has a larger cavity so it’s wider but it’s not as long. Why the difference? You can already guess that the larger cavity allows a woman to give birth. But why do males have narrow and long hipbones?

This specific shape gives the most weight bearing support for an animal that stands on two feet. Animals that use four legs do not need such strong hipbones because their weight was evenly distributed. Humans in contrast evolved large hipbones as they started to walk because they needed the vertical support. Likewise, to save resources, our shoulder blades become less dense, which is why we are prone to shoulder dislocations and clavicle breaks.

Anyway back to the point, males evolved this specific hip shape. Unfortunately for women, they do not have the ideal shape to allow bipedal operation. They had to find a compromise. Animals that are on four feet can have wide birth canals because their hips have a giant cavity. Humans cannot have such hips because there would be no support for the upper body, and your organs would comically sag down. So females have a compromise to allow childbirth and ability to walk on two feet. Since the hip is wider than it should be, the socket where the femur connects to the hipbone is angled slightly forward. In contrast, men have this socket straight out to the side. So we can run freely with the joint moving in one plane of motion. Women on the other hand, have to swing their hips in order to walk.

The “sexy catwalk walk” is a benefit, but there are some downsides. Women are more likely to get pelvis and joint pains because of added two plane motion. In addition, their legs don’t line up to the ground as parallel as men (due to the femur-pelvis angled connection), so there is a higher chance for knee injuries. Lastly, the female pelvis size explains why human babies are born so helpless, while some animals like deer can start walking immediately after birth. The cranial size is limited by the pelvis hole, so humans have adapted by giving birth early and delaying “survival maturity”. Any babies that were born with a super big head (and thus larger brain) resulted in the death of both baby and mother. Although technically, with the advent of C-section, I could see humans getting bigger heads (and thus brains). But we would have to wait at least tens of thousands of years. Damn it mother nature, just let us evolve gun hands already!

Anyway I’ve lost track of what I wanted to say: I thank my lucky stars that the difference in female pelvis bone gives them a sexy walk.

I searched "model walk" on youtube, and got something called "Walking With Mac"