The World's Tiniest Reptile Has Disproportionately Large Genitals

At just under 1 inch in length, Brookesia nana is thought to be the world’s smallest reptile. But this diminutive chameleon probably shouldn’t feel any self-consciousness about its size.

According to science, and relative to its size, the species has an absolutely enormous penis.

The genital dimensions of Brookesia nana were recently disclosed in a paper published in the journal Scientific Reports, which may or may not come wrapped in a brown paper bag. The chameleon, found in Madagascar, has hemipenes measuring 0.09 inches at full potential, or roughly one-tenth its entire body size. In fact, since length is measured by torso, it’s more like one-fifth.

If that weren’t enough, the chameleon’s hemipenes is actually a pair of penises. Why two? “The hemipenes serve exactly the same purpose as the mammalian penis, except that it doesn't have a tube going down it, but instead the sperm travels along a groove on the outside,” Mark Scherz, a co-author of the paper, tells Mental Floss. “Oh, and there are two of them, hence 'hemi,' and they are stored inside the body and one is everted during mating.”

Reptiles appear to have hemipenes owing to a genetic blueprint that takes its cues from hind (twin) legs. Practically speaking, they may alternate one hemipenis with the other, or use whichever one provides the best opportunity, depending on their position in relation to the female. Some reptiles, like snakes, may use their hemipenis to manufacture a mating plug that keeps other males from reproducing with the same female.

Why did nature provide such an endowment? The paper’s lead author, Frank Glaw of Germany’s Zoologische Staatssammlung München, asserts that the males need to make up for their overall size disadvantage with females that typically measure 1.13 inches in length. Scherz says that while Brookesia nana probably evolved into being small in response to the scant island resources available to them, their hemipenes needed to remain robust in order to copulate successfully. The male rides around on a female’s back until mating occurs. Given the physical proximity issues, larger hemipenes makes sense. In layperson’s terms, evolution had to make sure the hot dog still fit the bun.

We asked Scherz the obvious question: How large would a human’s penis be using the same relative size as the magnificently named B. nana? “Funnily enough, I hadn't done this math before, but I just did a back-of-the-envelope calculation and, based just on torso length, because legs are not part of the 'body' length we measure in chameleons … for a 6-foot, 2-inch man, it would be 17 cm, so 6.69 inches. Which, although above average for humans, is not so far above average to be ludicrous.”

B. nana can certainly strut around a locker room without shame. But the real bragging rights go to Brookesia tuberculata, another chameleon species that has hemipenes roughly one-third of its torso. In human terms, that would be positively equine. “The hemipenis of Brookesia tuberculata, on the other hand, would be 29 cm, so roughly 1 foot," Scherz says.