Why do humans menstruate when most animals don’t?
In: Biology
Short answer: We don’t know.
Long answer: There are some theories of why menstruation is only found in a few mammal species.
[Here](https://onlinelibrary.wiley.com/doi/full/10.1002/bies.201100099) are a few of them:
1. Menstruation evolved because it’s useful to clean the uterus from unused sperm.
2. Menstruation and the cyic regression are energetically more favorable than mantaining the endometrium in it’s active state.
3. Menstruation is “pre-conditioning” the uterus for the high level of inflammation and oxidatve stress during the placentation.
4. It’s a mechanical result after the spontaneous conversion of the cells inside the uterus (dezidualisation) which is normally induced by the embryo cells. However, it has beem observed that the dezidualisation is often induced spontaneously in higher primates during the pregnancy to force an abort of defect embryos.
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