Not only that. Menstruation started as a way to decrease the chance of non viable pregnancies (because we are susceptible to genetic mutations which we needed to in order to adapt). Because it reduced fertility, people had to fuck more often. Not only that, men were selected on certain traits that resulted in paternal care evolving. Because well... if the mom dies, then at least the dad makes sure they both succesfully reproduced. Male chimps are more likely to eat orphans than take care of em. After all, they can always force a another one.

Menstruation became so good at reducing fertility, that we developed monogamous behaviour. Men developed the ability to bond at all. By becomming more sensitive to oxytocin despite producing less of the stuff compared to women. Men also express prolactin in the brain after their baby is born, which is hard to find in other primates. It's amazing that men don't kill infants whereas male apes and monkeys do... just to get the female in estrus faster again.

I mean just look at the other primates. The males really don't care about anything except their position, and control over females. Whereas men can love interacting with dogs. Ever seen a cat dad? That's true care and love right there. It sounds like a "duh." But there is so much more behind the behaviour.

Humans are dope.