Anonymous
Anonymous asked in Science & MathematicsBiology · 2 months ago

Why did humans evolve to have a uterus instead of evolving to grow the fetus in the rectum or colon?

14 Answers

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  • Tom
    Lv 7
    1 month ago

    The rectum and Colon have other USES already.  

  • 1 month ago

    Because ALL mammals evolved to grow fetuses in the uterus. 

  • 1 month ago

    Mostly because the digestive tract is nasty.  (No, seriously...)  If you think about it, the human body is not solid, it is hollow because there is a tube that runs all the way through it from mouth to anus.  The throat, stomach, and intestines prevent a lot of germs from entering the blood stream.  There is barrier to isolate what we put in our mouths.

    The fetus structure certainly COULD have evolved to be part of the digestive system but because of the high throughput of germs it was strategically unfavorable.

  • Cowboy
    Lv 6
    1 month ago

    It's because our direct ancestors had a uterus before we came along - humans did not evolve the uterus, we inherited it.....

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  • 1 month ago

    And why no uterus in the nose or ear canal?  Ah, the mysteries of nature!

  • Anonymous
    1 month ago

    Humans are placental mammals, and all placental mammals have a uterus. So, we are not alone in having a uterus. Cows, dogs, cats, rats, whales, horses, monkeys, apes, elephants, and bats are all placental mammals and they all have a uterus. We simply inherited our uterus from the common ancestor of all placental mammals. The duck-billed platypus is an egg laying mammal and it has no uterus. Marsupials like the kangaroo, koala, opossum and sugar gliders have 2 uteruses. Placental mammals evolved from a marsupial and the 2 uteruses fused into a single one so placental mammals can have a bigger uterus for young that are in a more advanced stage of development before being born. As to why evolution happens one way instead of another, it is just due to chance mostly. Some animals such as lizards do have young born alive and these young do stay inside the intestine. We have evolved differently than lizards and snakes by chance. Live birth never evolved in birds. So, there is no one single way for evolution to happen. It is mostly luck but it also depends on what our ancestor had. Evolution happens in most cases by modifying existing structures instead of evolving a brand new structure from nothing. Birds for example modified their front limbs to evolve wings instead of evolving wings from nothing.  One advantage to having a uterus instead of keeping young in the intestine is that we and other placental mammals can continue to eat without having the waste products or poop going into the same area that the fetus is located. If we do it the other way, we would have to make sure we defecate regularly or else our fetus could be poisoned by our poop.

  • D g
    Lv 7
    2 months ago

    Think about your time in your mommy bowels 

    I'm wondering if she might be a bit constipated  after 9 months of you blocking the exit

  • 2 months ago

    Humans belong to the placental side of mammals. 

    Unlike monotremes (platypus...) placentals have separate openings for urination, defecation, and reproduction ("monotreme" literally means single opening) 

    Monotremes lay eggs and do everything from their cloaca..

     

    It's not clear when placentals diverged from monotremes and marsupials (Middle Jurassic to Late Cretaceous. The earliest undisputed placental fossil is as recent as Paleocene (after dinosaur extinction).

    Anyway (to answer the why question):

    The plus of placental reproduction is a better protection of the embryo inside the mother 

    The cons might be the vulnerability of the mother especially by the end of the gestation 

    It seems there were more pluses than cons.

  • 2 months ago

    cause thats the way god decided to do it

  • Orla
    Lv 6
    2 months ago

    You need to talk to your mom tonight.  Don't be embarrassed. 

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