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A handful of species on Earth share a seemingly mysterious trait: a menstrual cycle. We’re one of the select few mammals on Earth that menstruate, and we also do it more than any other animal, even though it’s a waste of nutrients, and can be a physical inconvenience. So where’s the sense in this uncommon biological process? TED-Ed describes the history and evolution of menstruation.

Lesson by TED-Ed, animation by TED-Ed.



  1. ribbitslant

    to people complaining about the title:
    yes, it’s “women”, and rightfully so since it refers to biological sex, not
    gender identity. it means “why do female bodies have periods”.

    yours sincerely,
    a person who hates political correctness hysteria

  2. HoneyStarsTwinkles

    dogs menstruat

  3. PillHead

    Well, this has been interesting. I just this wish this didn’t happen to me.

  4. pokemonpie

    Down. Thumbs down. Focus is off on this from its title.

  5. TwinkieStar

    The human female gets a raw deal from evolution.

  6. Enigma

    2:47 WTF is preeclampsia? This is for kids, so if you bring something ultra
    mega complicated up without saying what it is, then you are stupid.

  7. Avenger

    dogs menstruate too.

  8. prongwiki

    The male DNA wants the baby to exploit the woman as much as possible, while
    the female DNA tries to prevent it. I guess menstruation occurs because
    human male DNA is extra aggressive?

  9. FunkyIsland


  10. RichDramaBob

    Why do I feel like this is trying to make me not want kids???

  11. divinegale

    I wonder why a lot of women go crazy.

  12. cupcakesrock


  13. 123shuffle123

    I did not realize that there were other mammals that actually menstruated
    and not just “come into heat”. This was very interesting, to say the least.
    Most women of child-bearing age know that menstruation is the shedding of
    the lining. However, I did not know that the body shed the lining, and
    everything else, in order to prevent infection. I always thought that it
    shed the lining just as a mechanism to remove the unfertilized egg. The
    human body is extraordinary and the video does a great job explaining why
    menstruation is vital to the female reproductive system and body.

  14. kpobrien95

    So how then, does the heat cycle of all other female mammals work?