Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Genitalia: Why waste elimination AND reproduction?

  1. Mar 22, 2007 #1
    Why do genitalia serve this dual purpose? Is there some payoff or benefit for these organs to provide both functions of waste elimination and sexual reproduction?
  2. jcsd
  3. Mar 22, 2007 #2

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    A bunch of engineers are sitting around at a party, discussing the nature of God.

    The mechanical engineer states that God must also be a mechanical engineer because "if you look at all the pulleys and levers that drive the body, how the tendons and muscles and bones all work together, well, it's just amazing."

    The chemical engineer says that no, God has to be a chemical engineer because "if you look at all the chemical processes that drive the body, how the hormones and the brain and the glands and everything else all interact, well, it's just astounding."

    The electrical engineer says that no, God has to be an electrical engineer because "if you look at the circuitry of the body, how the thousands upon millions of nerve cells transmit signals from one part to another, well, it boggles the mind."

    The civil engineer speaks up last of all and says, no, God is definitely a civil engineer, because "only a civil engineer would run a sewer through a playground. "
  4. Mar 22, 2007 #3
    Ha! Thanks for that. So I guess it's one of those imponderables.
  5. Mar 22, 2007 #4

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Maybe, maybe not. Forgive me -- I was just having some fun with your legitimate scientific question.

    I figure if the reproductive doo-dads were tucked between the legs, it might be a slightly safer place where a predator bite would have trouble getting at them. So a critter might take a hit at the extremities, but still go on to reproduce.

    But we'll see what the biology mavens have to say...
  6. Mar 22, 2007 #5
    It also allow a more efficient use of resources.. why have two things when one is enough?
  7. Mar 23, 2007 #6

    jim mcnamara

    User Avatar

    Staff: Mentor

    There's an old dictum - phylogeny recapitulates ontogeny.

    Vertebrates all have pretty much the same body plan as we do. Our design comes from early vertebrates. As animals evolve, basic overall body plans and metabolic pathways change slowly or, more correctly, tend to be conserved. This is why all of the vertebrates have bilateral symmetry, for example. And why waste excretion openings and genitalia tend to be in very close proximity in most vertebrate species.

    Why fix it if it ain't broke?
  8. Mar 23, 2007 #7
    Well, I expected that. But why did the proximity exist in the first place? Surely it's not just coincidental.
  9. Mar 23, 2007 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Why not?

    Unlike lower invertebrates, we have separation of ingestive and excretory openings. It also makes sense to have the fewest openings from the outside to the inside (the digestive tract really provides a closed tube through the body) so that the potential for infection penetrating the body cavity is reduced.
  10. Apr 2, 2007 #9
    Fewer infections, hence lower mortality rate, hence better rate of survival, genes passed on...Hey-Presto, a genitila with two functions. :surprised

    Funnily enough, you can't do "both" things at the same time. It's physically impossible.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook