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How Lurking Predators Changed the Size of the Mosquitofish's Genitals

Female mosquitofish give birth to tiny babies, like the guppies you may remember from your third-grade aquarium. That means male mosquitofish don’t spawn: if they’re going to be dads, they need to use a modified fin (called a gonopodium) to inseminate their mate. And sex with a long, stiff fin demands a daunting level… » 8/25/15 8:00am Tuesday 8:00am

How That Butt-to-Butt Stage of Dog Mating Happens

If you’ve ever watched a pair of dogs have sex, you’ve probably noticed something odd happen partway through the act. At first, the male grips the female’s back and humps away–nothing unusual about it. But then he dismounts and turns to face away from his mate, with his penis still stuck inside her. » 8/11/15 11:31am 8/11/15 11:31am

Women Really Don't Notice Details About Your Penis

We’ve seen it in study after study: men worry about what their penis looks like. Is it too short? Too long? Too thin? Is the glans too fat? Will that birthmark be a deal breaker? Relax. A study published in the Journal of Sexual Medicine last month suggests that women don’t really notice those details.
» 8/06/15 8:33am 8/06/15 8:33am

Here's an Anatomical Structure We've Never Seen in the Penis Before

You already know that a penis has arteries to bring blood to its erectile tissues, and veins that take the blood away again when it returns to its normal flaccid state. You may not know that there’s another set of vessels tucked under its skin. We just got our first good look at them. » 7/21/15 10:48am 7/21/15 10:48am

It's True, Scar Tissue Can Bend Your Penis (NSFW)

It’s normal for a penis to curve a little when it’s erect, but Peyronie’s disease pushes that curve to alarming extremes. It doesn’t usually muck with a guy’s ability to get it up, but once the penis is erect, it can deviate 30° or more from its normal line of action. The curvature can be so severe it interferes with… » 6/22/15 11:30am 6/22/15 11:30am