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I do understand that the female has to prepare for possible fertilization and make sure that the egg is of the best quality, so they try to remove aged egga from the uterine. However why cant the body just simply get rid of the egg not the uterine lining? Maybe like reabsorb the egg or pass them out as waste? I mean its extremely energy consuming etc and it would be an evolutionary disadvantage since many other mammals dont go through menses.

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