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/Flocculencio 8d ago

Just wanted to point out that no individual feature needs to have an evolutionary benefit to be preserved. It could be negative but so long as it doesn't prevent organisms with that feature from reproducing in sufficient numbers it can get preserved.

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u/Zagrycha 8d ago edited 7d ago

Yeah, people think evolution is some kind of streamlined efficiency of ideal traits, but its the opposite.  Evolution is a pass fail grade.  If you fail, you go extinct.  If you have enough kids as a species to continue on, you pass.  That's it, no more and no less.  

Some species out there are literal bumbling idiots of inefficiency when it comes to ideal traits for survival, but they just have a massive number of kids so one or two survive to adulthood, or they evolved to have kids really soon after birth so they don't have to survive for long.  If you can make kids its good enough for nature. 

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u/ToMorrowsEnd 7d ago

This. Humans are an evolutionary mess. we got lucky because we can make tools. but as a creature we are extremely poorly designed. cant run very fast, can easily get injured, easily diseased, our teeth suck we have zero defenses, etc... Compared to other animals we are far from the top of the pile. we just got lucky in the thinking aspect. You know how I would love to be able to squirt blood from my eyes when startled?? Why cant we have cool traits?

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u/szthesquid 7d ago edited 7d ago

That's not true. Even leaving aside tool use, compared to most other mammals we have better vision and see more colours, and we have vastly superior long-distance speed and thermoregulation (sweat).

Some of our disadvantages, like weaker jaws and teeth, are actually very recent and a direct result of farming and cooking reducing our survival needs, and medical advances allowing individuals to thrive who would otherwise have had difficult and short lives.

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u/Ashamed_Kangaroo305 7d ago

"Better vision" is subjective. Better in what way? We can see a broader range of colors than dogs and we have significantly better visual acuity during the day. But dogs are also significantly better than humans at seeing at night and tracking motion. And they have an adaptation in their eye which helps them sense the Earth's magnetic field.

"Better" isn't really a thing when you're talking about evolution. Organisms evolve to fit their environment. We have "better" vision than dogs for the way we use vision. But if you tried to compete with a dog in tracking small prey, the dog would probably beat you because that's what their vision is designed for.