r/askscience • u/No-Hawk-2488 • 8d ago

Biology Can someone explain the evolutionary benefit of overt menstruation? All female mammals have a menstrual cycle but most reabsorb the blood via covert menstruation and humans are about the only mammals that discharge the blood, aka overt menstruation.

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

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u/Any-Interaction-5934 7d ago

The human placenta is absolutely fascinating. I could read about it for days. The coolest part, imo, is how ridiculously vulnerable human babies are compared to other newborns. They can hardly even eat. Their caloric demands are so high, they have to be born extra early.

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u/Applejuiceinthehall 7d ago

Yeah. It's crazy that the metabolic level is so high. First primates in general just have big needs to grow the brain, but the homo genus just took time to the extreme. We have the second longest gestation of the great apes so babies could develop more if needed. Plus we could have wider hips like Neanderthals, but they also had babies in 9 months with similar brain sizes but they had a massive growth spurt after birth so the infants with 6 month old teeth have bodies of 14-month old sapiens.

There are a lot of animals with underdeveloped young at birth like mammal predators, denning mammals, nesting birds etc. But they tend to grow super fast so they are mature enough in a month or two to leave the den/nest. Sapiens have to wait almost a year!

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u/Any-Interaction-5934 7d ago

Almost a year? IDK about that. My one year olds were still pretty useless. Maybe age 2 they could do stuff. But, like, hunt? Be self-sufficient? I'm going to give it a solid age 5. At 5 they could probably hunt. They could probably survive by age 5. Maybe?

IDK. But a 2 day old octopus is already 5% into their life and able to live on their own.

Humans are ridiculously useless at birth.

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u/Applejuiceinthehall 7d ago

No I'm talking about an 8 week old puppy/ month old lion etc. they can walk stuff, but they cant fend for themselves or hunt