What are the obvious differences between men and women?

[Like Ra]

That's more related to proportions - wider hips, different hip angle.

A woman walks with a sway in her hips.

Yep. And this is important.

His stride and sitting is a lot wider. Probably it’s the fact he has a third leg

I don't think this is the reason. With wider hips and more freedom in the joints, it would be easier and more natural for women to sit (and walk) with legs apart. Just like how pregnant women sit.