This episode is also on Bilibili too.
Where did the human male penis bone go? There’s no bone in a man’s penis; when it really counts, the whole thing relies on the corpus cavernosum to stand at attention. But many mammals do have a bone in the penis—dogs, cats, rats, bears, raccoons, otters, and bats, for example. They don’t need to work so hard to get things standing; they have a baculum and can rise to the occasion anytime. So why are human males so damn unlucky?
Hi everyone, I’m Zhichao Wei. In today’s episode, we’re talking about why men lost the baculum in evolution.
Let’s begin with a curious case from an old myth.
You surely know the story of God creating Adam and Eve. In Genesis, God first created Adam in his own image. Later, worried that Adam was lonely, he took one of Adam’s ribs and made Eve. Hence the old saying that woman is man’s rib.
But here’s the question: Did God really create Eve from Adam’s rib?
If we seriously stop and examine the story, the claim starts to look pretty suspicious:
Men and women plainly have the same number of ribs, with equal numbers on the left and right. If the ‘rib removal’ story were literally true, Adam must have been created with one extra rib in either the left or the right side of his chest.
Adam’s skeleton was originally asymmetrical? That would be aesthetically unacceptable! After all, God made Adam in his own image.
So what God took from Adam should not have been a rib, but a bone appearing on the body’s midline. Only removing a bone from the midline would leave left-right symmetry intact.
A reasonable guess is that the ancient people who came up with the story of God creating humans had noticed that men were missing a bone on the body’s midline—a bone that seemed as if it ought to be there. It may have existed in many male animals, yet was nowhere to be found in men. Naturally, the ancients wondered: where did it go? They used their imaginations and said: God took it out and made woman from it.
And by connecting this missing bone with the two sexes, the ancients were implying that its location probably had something to do with reproduction and fertility.
So the answer is practically shouting at us—
What God took from Adam was the baculum.
As I said at the beginning, men really don’t have a bone in the penis. Among primates, that’s actually highly unusual: gorillas, chimpanzees, and our other close relatives all have bacula. Only two primate species lost the baculum during evolution: spider monkeys and us humans.
If humans did have a baculum, it would sit right on the body’s midline. Add one or subtract one, and it wouldn’t affect bodily symmetry; it would also obviously be closely connected with sex.
So if you ask which bone God used to create Eve from Adam, the baculum is, logically speaking, a much smoother answer than the rib.
That was my logical reconstruction. But this idea isn’t merely logically plausible; there’s textual evidence too.
The idea that ‘God used Adam’s baculum to create Eve’ was first proposed by two American scholars on the basis of evidence in the biblical text.
In 2001, developmental biologist Scott Gilbert of Swarthmore College and biblical scholar Ziony Zevit of UCLA published a paper:
Gilbert, S. F., & Zevit, Z. (2001). Congenital human baculum deficiency: The generative bone of Genesis 2: 21–23.American Journal of Medical Genetics,101(3), 284-285.[i]
They pointed out that the word translated as ‘rib’ in the English Bible is tzela in the older Hebrew Bible. It can indeed mean ‘rib,’ but elsewhere in the Bible it can also mean a ‘ridge,’ or a pillar made of pine or fir, or a support in a building. So the word’s original sense may well have referred to various kinds of—structural support beams.
‘Structural support beam’ is almost absurdly perfect as a description of what the baculum does. Male animals with a baculum rely on this bone to support the penis and support the mechanics of an erection.
The two scholars also found an anatomical clue in the biblical text:
After God took Adam’s ‘rib,’ Genesis immediately says: ‘The Lord God closed up the flesh.’ (The Lord God closed up the flesh).
The complete sentence is: ‘While he slept deeply, he drew out one of his ribs, then closed the flesh back up.’ (Translated by Feng Xiang.)
In the scholars’ view, this detail about ‘closing the flesh back up’ reflects a distinctive anatomical feature of the human male penis and scrotum—the raphe, the crease running from the scrotum all the way to the urethral opening. That crease looks remarkably like a wound that has been stitched closed. (A little ball-crushing to hear, isn’t it~)
A stitched-up wound, with a ‘bone that should have been there’ missing inside—and the whole area connected with reproduction. If you were an ancient person who noticed those features, how would you explain them? If it were me, I’d let my imagination run like this:
Once upon a time there was a God. God created man, then worried that man was lonely, so he took the man’s baculum and created woman.
—Isn’t that just Genesis?
In the legend, God took away the male baculum. But scientifically, how do we explain why human males lost it in evolution?
In The Evolution of Beauty, Yale biologist Richard Prum offers two explanations[ii].
The first is the ‘health signal hypothesis.’
This hypothesis was proposed by Richard Dawkins, author of The Selfish Gene. Dawkins argues that a penis with a baculum never encounters erection difficulties, while getting a baculum-free penis to become and stay erect requires a man to be healthy and physically robust. So whether a baculum-free penis can rise firmly becomes a reliable signal of male health—one that is basically impossible to fake. Women can then use that signal to judge whether the men courting them are healthy enough.
That’s the ‘health signal hypothesis.’ It’s already quite a leap, but the next theory takes the imaginative leap ten times farther.
The second explanation for why human males have no baculum is the aesthetic hypothesis.
This hypothesis was proposed by Richard Prum himself, the author of The Evolution of Beauty. Prum thinks Dawkins’s explanation simply doesn’t hold water: almost 100% of young adult men can get erections after puberty, while erection problems occur almost entirely among middle-aged and older men. In prehistoric times, men probably died long before erection problems showed up, so how could erection ability have signaled good health?
Prum thinks his ‘aesthetic hypothesis’ is more convincing. He argues that losing the baculum satisfied the aesthetic preferences of human females.
First, relative to body size, the human male penis is terrifyingly large—far larger than those of other primates. This may have evolved to satisfy female aesthetic preferences: bigger looks better than smaller.
Second, when male animals with bacula are not erect, the penis is usually tucked away, shrunk up and invisible. A penis without a baculum, by contrast, hangs outside the body.
Put those two points together. Before clothing that hid the lower body—and the corresponding culture of modesty—appeared, a penis that hung below the body because it had lost its baculum, swaying and swinging, and frighteningly large compared with other primates, would have been a spectacular view for prehistoric women to enjoy anytime, anywhere. In deep prehistory, how beautiful this ‘view’ on a man looked could have greatly affected women’s evaluations of him, and therefore the outcome of mate choice.
So a penis without a baculum is not a display of bodily health at all; it is a display of beauty.
That is the ‘aesthetic hypothesis’ for why human males have no baculum.
After reading Professor Prum’s hypothesis, I couldn’t help thinking of a lovely poem by Wang Xiaobo:
Walking through the silence,
Walking through the sky,
while the penis hangs upside down.
References:
[i] Gilbert, S. F., & Zevit, Z. (2001). Congenital human baculum deficiency: The generative bone of Genesis 2: 21–23.American Journal of Medical Genetics,101(3), 284-285.
[ii] Richard O. Prum. (2019). The Evolution of Beauty: Darwins Forgotten Theory of Mate Choice and How It Shapes the Animal World—and Us. CITIC Press.
Leave a Reply