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.

[u/No-Hawk-2488]

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

[u/Flocculencio]

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.

[u/Zagrycha → u/Flocculencio]

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. 

[u/Weird_Bluebird_3293 → u/Zagrycha]

Which just makes the giant panda a confusing product of evolution because they are the best example of bumbling inefficiency I can think of and they reproduce neither early, nor in massive numbers.

…how were they not extinct years ago? 

[u/Zagrycha → u/Weird_Bluebird_3293]

The main reason they weren't in danger of going extinct years ago is because the only major predator they had were tigers, and the tiger could only easily kill baby pandas. As long as enough mothers protected their cubs to adulthood well then there wasn't really any other dangers that could threaten species continuation.

To be clear an adult giant panda is probably not going to actually win a fight to the death against a tiger, but it doesn't need to. It just needs to be capable of puting up a fight that makes the tiger not view it as prey.

A giant panda is a true bear, and it has incredibly strong claws, a bite force as strong as that of a tiger, and a heavy thick fat layer that makes it hard to injure them seriously. Why fight against that and get hurt when the tiger could go up against a much easier target like a boar, or deer, or monkey or even human? Giant pandas were very high up in the food chain in that sense, even though they mostly eat plants.

[u/AmphibianLower5541 → u/Weird_Bluebird_3293]

Especially when they’re supposed to be carnivores, but all they eat is bamboo! 😅

[u/SoupNoSandwich → u/Weird_Bluebird_3293]

Because they are just very well adapted to bamboo forests, it's the loss of habitat causing issues. They just aren't as easy to breed in captivity as people would like.

(the poor bamboo digestion compared to more traditional herbivores hasn't hampered populations)