Why Do We Call Erections "Boners"? Here's What Science Says
Andrew Zaeh for Bustle
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If you were in elementary school any time during the past 40 years, you probably know what the term “boner” means. The word alone conjures giggles and images of elbowing your friend to see if they got it, too. Boner! Ha ha! It means a hard penis! But have you ever stopped to think about why we call it a boner? According to science, the root to the term might lie in the penis bone — but not human ones.

In third grade, you may have thought we used the word boner because hard penises have actual bones in them. Hopefully you’ve long since figured out that’s not the case, but just to clarify, while erect human penises are “hard” (and you can “break” them), that stiffness is from blood filling up the two cylinder-shaped chambers in the shaft. There’s no actual bone inside the human penis.

However, penis bones — the technical term is “baculum” but I’m going to use penis bones instead — are totally a thing. Beth Mole recently reported in Ars Technica about a new study published in Proceedings of the Royal Society and conducted by anthropologists at the University College London that examined the penis bones and mating habits of our closest evolutionary relatives. They found no penis bones in our evolutionary ancestors about 145 million years ago, when placental mammals spit from non-placental mammals. (Placental mammals are mammals that have live young, while non-placental mammals are mammals that carry their young in a pouch in the early stages of life. Think cats versus kangaroos.)

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But as recently as 95 million years ago, when primates and carnivores — our closest evolutionary ancestors — evolved, penis bones appeared. And today, primates such as the gorilla, chimpanzee, and bonobos all have penis bones — but human beings are conspicuously missing the penis bone-enhanced boner. So what gives?

The University College London researchers examined the mating habits of animals with penis bones and those without. They found that longer penis bones were associated with a longer amount of time spent actually having vaginal intercourse. They also found that species with penis bones had more competition for females than those without, suggesting that the longer time spent boning was probably related to keeping the female occupied long enough for sperm to implant before another male could take his turn.

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Similarly, there are theories that human male penises have a “mushroom tip” because it creates suction that pulls out any semen from other men that’s hanging around up there. It’s called “sperm displacement theory” and it could be how human males evolved to have no penis bone.

Ultimately, it seems the reason human males don’t have bones in their penises has to do with the way humans have sex. But theories about the etymology of the word boner are pretty vague — some sources say it comes from a 1940s term “bone-on,” which was itself an evolution of the term “hard-on” from the late 19th Century.

But even though human male penises no longer have bones — and the science of language can’t trace exactly where the word “boner” came from — the connection between the two is kind of irresistible, isn’t it?