The very irksome reason the penis is shaped the way it is.

Penises are weird and that is a fact.

If you’ve ever come into contact with a human penis, you’ll have noticed that it’s unnecessarily aggressive and looks more like a mushroom than anyone ever warned you. Testicles are also confronting but that’s a topic for later.

Most of the time we’re fine with penises and their surrounding… environment. Genitals aren’t meant to be beautiful and frankly, the majority of us are far more concerned with what a penis can do than what it looks like. But when you learn why a penis looks the way it does, suddenly nothing is okay. At all.

In his book Why Is The Penis Shaped Like That and Other Reflections on Being Human, psychologist and associate professor Jesse Bering cites the work of evolutionary psychologist Gordon Gallup, who theorised that the human penis really is a ‘tool’ that’s been manufactured over hundreds of thousands of years.

He argues that objectively, there are significant differences between the human penis and the penises of other species. Most notably, the human penis is especially large, and has “a distinctive mushroom-capped glans” that forms a coronal ridge underneath.

Here’s a diagram I made from scratch:

Image via Wikipedia.

After a great deal of research, including magnetic imaging studies of heterosexual men and women having sex (which seems kinda... private, but okay), Gallup and his colleague Rebecca Burch concluded the following:

"A longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity." - Journal of Evolutionary Psychology.

The key words here are 'displacement of semen'.

The semen displacement theory states that since sperm can live for a number of days in a woman's cervical mucus, if she has more than one sexual partner within a short period of time, the sperm of these men are competing to fertilise an egg. Therefore, the male penis has been sculpted with the purpose of 'displacing' the semen of other men from a woman's vagina. The coronal ridge serves as a removal device that 'scoops out' other men's sperm, so that it is the current sexual partner's sperm, and not a competitor's, that reaches the cervix.

Bering describes this as "a well-synchronized effect facilitated by the 'upsuck' of thrusting during intercourse" and I am not even a little bit okay with his use of the term 'upsuck'.


LISTEN: Porn star Madison Missina delves into the different shapes, sizes and curves of penises, and how each one affects sex. Post continues after audio.

This theory might also explain why men become flaccid quickly after sex, such that continuing to engage in sexual activity is actually uncomfortable. "Continued thrusting would be self-defeating," Bering writes, as "the man would essentially be removing his own sperm at that point".

A lot of things are making sense right now and it's all very unsettling.

While evolutionary psychology is necessarily theoretical, several studies have been able to support Gallup's hypothesis. Indeed, it seems the penis really does act as a 'scooping mechanism', whether we like it or not.

Bering ends his reflections on the human penis with a reminder that we should be glad we're not cats. Male cats have penises equipped with over 100 sharp barbs that rake the walls of the female's vagina.


It's thought that this super violent adaptation serves to trigger ovulation, displace the sperm of other male cats, and stop the female cat escaping during sex. Which it just... definitely wants to.

So if you find yourself having sex with a male person any time soon, be aware that he's unconsciously trying to scoop the semen of other sex partners out of your vagina.

Which is rude.