If you're a man, you're lucky you don't have to give birth. I'm glad we're an intelligent species, but boy, that infant head feels mighty large going through that narrow birth canal. And then, after all that, the baby comes out facing down and backwards, which means you're helpless to assist it, or even to untangle it from the umbilical cord.

According to evolutionary anthropologists, babies of the earliest humans had a fifty-fifty chance of coming out facing backwards. This was a result of humans learning to walk on two feet. As the pelvis became optimized for walking, the birth canal developed twists and turns that meant the baby had to rotate in order to keep its head and shoulders aligned with the widest part at all times.

Over time, our brains also got bigger, which meant more twists and turns. Some of the earliest humans learned to compensate for the difficulty of giving birth by receiving assistance during childbirth, which made a huge difference in terms of survival.

Some anthropologists think that there's an evolutionary advantage to having someone help you give birth. They conjecture that human females who gave birth to backwards-facing babies, and females who had assistance because they felt particularly anxious about the birth, ended up doing better than females who didn't. After all, if problems arise during labor, having another person around can make the difference between life and death.