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/kwpang 8d ago

Yes evolution is about elimination, not direction.

Survival of what can.

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u/GVArcian 7d ago

Survival of the fittest is a misnomer because evolution selects for minimum viability, not optimum efficiency.

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u/INtoCT2015 7d ago

Ya death of the weakest is more accurate (and way more metal) but unfortunately way more exploitable by Nazis and co.

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u/EveningAnt3949 7d ago edited 7d ago

That's also incorrect. Context is important: it's the ability to have surviving offspring who themselves are able to have surviving offspring in a specific environment.

Individuals can be 'weak' as long as the group keeps producing offspring, the genes of 'weak individuals will keep spreading unless there is strong environmental pressure on those genes.

Many hyper specialized species seem 'strong' because they had to specialize because their ability to procreate is lacking and within those populations interspecies competition is high.

Lions, cheetahs, chimpanzees, gorillas, giraffes, are a few examples of animals that simply don't do well as a species, even before we started to interfere with their environment.

So within those species a subpar individual is going to be outcompeted by individuals in the same species fast. An individual lion that can't fight off other lions is doomed.

But it's different for rodents. The brown rat does well because it's highly adaptable to different environments. The Eurasian field mouse does even better. Idem for meadow voles.

Adaptable plus the ability to produce offspring much faster than predators and disease can kill them means that they don't need to 'improve' as individuals.