Wow! I was just thinking how much the pelvic girdle had to change by evolution before species could stand up and walk. And there must have been a lot of failed births until the female body evolved to the point where everything worked right for the pregnancy and the birth was successful.
I can't imagine how much trial and error went on in the evolution of hormones. Hormones produced during pregnancy signal the joints in the pelvic girdle to loosen up.