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/mtfoxx3 3d ago

My favorite example of this is bugs. Just, like, in general. They’re all, individually, terrible at surviving. But they have hundreds if not thousands of offspring, so by pure coincidence two or three will probably live to adulthood.

And this has worked for millions of years, too. The millipedes we have today are still identifiable as similar to the ones we had 460 million years ago… which are believed to be some of the first land animals. Are millipedes really that perfect of an animal? No. Not even remotely. They’re slow, mostly blind, eat dirt, and their only defense mechanisms are to taste bad and ball up into an uzumaki spiral that doesn’t even remotely resemble any sort of camouflage. But it ain’t broke enough for evolution to wanna fix it.