• Question: how come females's have periods and boys dont?

    Asked by mollymoo to Cesar, Emily, Jamie, Kate, Philippa on 15 Jun 2011.
    • Photo: Jamie Gallagher

      Jamie Gallagher answered on 14 Jun 2011:

      Girls have to prepare a lining that could nestle a little egg if it becomes fertilised. If the lining isn’t used it is disposed of. As boys don’t carry the eggs or the babies there is no need for a period. Boys can reproduce and don’t have a natural cycle.

    • Photo: Emily Robinson

      Emily Robinson answered on 15 Jun 2011:

      Another interesting fact is that females are born with all of their eggs, so there is a definitive number and no more when they are used up, where as men are constantly producing sperm. So female bodies have to be more organised about releasing their eggs so not to waste them. A fertilised egg will grow in the womens womb thats why once a month this lining needs to be changed so that when an egg is ready it has the best chance of surviving to become a baby.

    • Photo: Kate Clancy

      Kate Clancy answered on 15 Jun 2011:

      As someone who studies that lining for a living, I can even add a bit more!

      First, females have a uterus and males do not. Since periods are made of the lining of the uterus, this answers the question quite neatly!

      But why do girls have periods? That is very interesting, because there are plenty of other species with uteruses and uterine linings, but they just resorb it back into their body each cycle. We seem to have a lot more lining to get rid of at the end of each cycle.

      It looks like the answer is related to what I talked about in another question, regarding how human babies are made:

      /copperj11-zone/2011/06/how-are-babies-made

      Our fertilized eggs need to burrow really far into a thick, lush lining in order to survive. They need to feed off the nutrients from that lining while the placenta is being built. And so in order to deal with our really invasive fetuses, which are invasive largely because they need the extra calories to feed their big brains, we needed to make thick linings.

      Then, we have too much lining to easily resorb it. So the only other way to get rid of it is to have a period!

      So every time you get your period, you should actually feel like it’s kinda cool, because it’s a product of human evolution that is related to our large brain size!!!

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