Skip To Content
    Nov 6, 2014

    Scientist Now Know Why Humans Only Have One Penis

    Anacondas don't want none unless you have two penises hun.

    Research published in this week's Nature solves the mystery of why snakes and lizards develop pairs of genitalia while the rest of us don't.

    Tess Thornton / / CC

    Species lucky enough to have two penises do so because the genitals develop from cells located near the legs, or where the legs would have been.

    Alex Popovkin / Flickr: plants_of_russian_in_brazil / CC

    Whereas species that only have one penis do so because the genitals develop from cells near the tail, or where the tail would have been.

    So next time someone refers to their member as their third leg, please correct them — it is actually more like a tail.

    The genitalia of all species develop from something called the cloaca. The location of this cloaca is the key to whether an animal ends up with two sets of junk or not.

    Jared Yelton / / CC

    In most mammals the cloaca is only an embryonic structure (some types of cloaca are still present in marsupials and egg laying mammals known as monotremes). As the embryo develops, the cloaca splits into the anus and urethra (and in females the vagina). Birds, however, keep their cloaca intact, and use it for feces and urine excretion as well as reproduction. Nice huh?

    When embryos develop the cloaca sends out a signal to the surrounding cells triggering the growth of genitals.

    Patrick Tschopp, PhD; Harvard Medical School, Department of Genetics
    Patrick Tschopp, PhD; Harvard Medical School, Department of Genetics

    Patrick Tschopp and his team from Harvard Medical School studied the development of embryos of mice, anoles (a type of lizard), house snakes, and pythons. In the mouse embryo the cloaca is futher back near the cells destined to become a tail, and the mouse ends up with just the one penis. While in the reptiles the cloaca is closer to the potential legs, and they develop two penises.

    It's a bit farfetched, but this may eventually help us understand syndromes in humans that occur when these signals aren't given, or not at the right time, or not for long enough

    Here is what snakes look like using their penises in case you wondered. / Flo Perry / BuzzFeed

    (But they actually only use one at a time so sucks to be them.)

    BuzzFeed Daily

    Keep up with the latest daily buzz with the BuzzFeed Daily newsletter!

    Newsletter signup form