We’re not missing the penis bone, we just lost it

** Hey y’all – it has come to my attention that the article this post is criticizing might have been more of a tongue-in-cheek textual criticism than a literal hypothesis (like I treated it). Instead of it being “this is what we think is true” opinion, I think it’s more of a “this interpretation of the Bible is more justified by the natural world”. Read at your own risk and sorry for my confusion. – S.Hird **

During his Society of Systematic Biologists presidential address at this year’s Evolution meeting, Jack Sullivan mentioned a rather…unusual…article. (Well, letter, technically.) Congenital Human Baculum Deficiency, by Scott Gilbert and Ziony Zevit was published in the American Journal of Medical Genetics in 2001; it describes their hypothesis that Genesis 2:21-23 doesn’t mean Eve came from one of Adam’s ribs, she came from his baculum.

Walruses have bacula almost 2 feet long – it is required that a picture of a walrus accompany any discussion of bacula.

What’s that, you say? Baculum is the technical term for the penis bone. Many mammals have one – presumably to aid in sexual intercourse. For mammals that mate infrequently, prolonged intercourse ups the chances that a particular male sires some babies. For mammals that must mate quickly, the baculum provides immediate rigidity. And for all mammals, keeping the urethra straight while copulating is imperative, so maybe it’s there to prevent a kink in the works, so to speak. The truth is, there are a lot of hypotheses about what bacula do but – as you might imagine – they’re kind of difficult to test. Regardless, our nearest evolutionary neighbors, the great apes, all have bacula, as do most other primates. Gilbert and Zevit cite this– the fact that our baculum is missing – as evidence for their argument. Which goes like this:

  1. A rib seems like an unlikely origin for Eve because male and female humans have the same number of ribs.
  2. Ribs also lack “intrinsic generative capacity”, which penises have “in practice, in mythology, and in the popular imagination”.
  3. Most mammals – and especially primates – have bacula, humans do not.
  4. It is therefore “probable” that Adam’s baculum was removed to make Eve, and not a rib.

The authors then continue to support their argument with alternate translations of the Hebrew word for “rib” (which they say could mean “support beam”) and claim the raphe of the human male scrotum is what Genesis 2:21 is referring to when it says “The Lord God closed up the flesh.”** I’m almost convinced!

Almost. Lots of evolutionary innovation occurs through gaining functions, but losing functions (or appendages) also happens. Humans are different from the other great apes in a lot of ways – did you know we’re the only ones with chins? Just because we’re related but lack an otherwise common trait doesn’t mean God took it from us. It’s also interesting to note that some species – like the walrus – have gigantic bacula (like 22 inches gigantic and the largest fossilized baculum from an extinct walrus species comes in at 4 feet). Great apes have much, much smaller bacula – and the closer they are to us, the smaller it is (Figure 1).

Figure 1: (A) Real phylogeny and real bacular data on great apes. (B) Perhaps slightly misleading representation of the relationship between great apes and bacula

Figure 1: (left) Real phylogeny and real bacular data on great apes. (right) Perhaps slightly misleading representation of the relationship between great apes and bacula

Why do humans lack a baculum? Well, there are several theories. Richard Dawkins has hypothesized that sexual selection is responsible, as erectile function may be an honest signal of a potential mate’s health***. Perhaps our mating system – which allows for more and shorter copulations instead of infrequent and longer copulations – made them costly and useless enough to be selected against. Or maybe the bacula serve no purpose – they’re vestigial in great apes. There is a lot of speculation about the “missing” human baculum on the internet and scientific literature – I’m almost embarrassed to be adding to the load – but the point here is that this argument is an odd mix of science and creationism and the end result is a story that makes less sense than if the authors had stuck to one or the other. They invoke phylogenetic concepts to justify their religious opinion – basically, they’re saying “Our nearest evolutionary relatives have bacula (as do most members of our clade Mammalia), so if we don’t have one, God must have taken it – to produce female human beings.”

That last clause there – the part where it creates the second gender, is the part I get least when I consider the distribution of bacula across the animal kingdom. I know humans are special but still – why do some animals have bacula at all? I’m trying to not be disrespectful and snarky – but seriously, this argument is inconsistent with the natural world. Bacula ossify by a different mechanism than, say, your femur – it’s not part of the main skeletal system. This may allow it to be more easily lost and/or gained through time and could help explain why we (and spider monkeys and whales and hyenas and ungulates) aren’t really “missing” it, we just lost it.

* (from figure) data obtained from: http://www.primateportal.org/normative-values/baculum-length-glans-penis-length-and-length-erect-penis-adult-male-primates

** For what it’s worth, women also have a perineal raphe.

*** Something about this Dawkin’s quote – regarding humans and bacula – is too good not to include here: “It is not implausible that, with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male’s health, and robustness of his ability to cope with stress, from the tone and bearing of his penis.” The Selfish Gene, 30th Anniversary Edition

(No, no I would not classify myself as mature for my age.)

Twippy the Clown  (No, no I’m not very mature for my age.)

Gilbert and Zevit. 2001. Congenital human baculum deficiency: The generative bone of Genesis 2:21-23. American Journal of Medical Genetics, 101(3):284-285.

The above is a link to the journal article (which is behind a pay-wall) – the full text of the article is available here.

13 comments on “We’re not missing the penis bone, we just lost it

  1. Chris Smith says:

    I am appalled, Sarah Hird.

    Appalled by your (admittedly) misleading of phylogeny to imply an evolutionary trend. Chimpanzees are not more closely related to humans than are Bonobos, but by rotating the taxa in your tree you’ve made it appear that there is a progression towards smaller bacula. Second, in your scatter plot, you’ve represented each of your taxa as independent evolutionary events.


    (And an awesome post)

    • Hird says:

      It’s true! It’s all true! The shame! The horror. Seriously, though, I’m aware of my sins. In my defense, the scatter plot would look basically the same if chimp and bonobo shared a spot on the axis or even if they switched order (so maybe I should have just made it more accurately). Or maybe there is an evolutionary trend? Selection for sociality selects against bacula – something like that? Ok, ok, total lack of evidence but it could be! We should let peer review decide – I’ll be submitting this blog post to Science this afternoon and we’ll see who has the last laugh.

  2. Chris Smith says:

    I was also surprised by the scale on the y-axis. Is the Bonobo baculum seriously less than a centimeter in size? Vestigial indeed.

  3. Tor Bertin says:

    Is the baculum size given in Figure 1 scaled by body size, or are those raw values?

    • Hird says:

      I believe they’re raw measurements but I included the link to the data with the first * up there, so please feel free to correct me if that’s wrong!

  4. The authors Scott F. Gilbert and Ziony Zevitexplicitly say: “One of the creation stories in Genesis may be an explanatory myth wherein the Bible attempts to find a cause for why human males lack this particular bone.”

    Hence, their whole performance is medically and anatomically informed textual criticism – not creationism!

    Creationism is uncritically taking scripture at face value and at the most shallow at that. That is, creationists will stick to the most superficial reading where god literally took a rib from Adam.

    Textual criticism is is concerned with the identification and removal of transcription errors in the texts of manuscripts including scripture. It’s part of language sciences.

    If you are already giving quotes of Dawkins’s The selfish gene, he has an erudite footnote on how Mary may have become a virgin by way of transcription errors (from Aramaic to Greek to Latin), that is, he cites findings of textual criticism. You don’t suppose that he therefore is a creationist – do you?!

    • Hird says:

      Hi Joachim – Thank you for this comment! It is totally reframing how I view this letter. Is it supposed to be tongue-in-cheek? That sentence you quote actually really confused me when I read the article and thinking about it as “The ‘God took a piece of Adam to make Eve’ story in Genesis may be the Bible’s attempt to explain why humans lack a baculum.” makes WAY more sense than what they wrote. I may have totally misread what they’re trying to say (I’m going to put a note at the top of this article saying something to that effect). In my defense, though, they then say “Our opinion is that Adam did not lose a rib in the creation of Eve.”- As if they actually believe Eve was created when God took something from Adam – not just think the myth should be reworded. I wish they had spoken in terms of “Our opinion is that the creation myth of Adam and Eve might be more scientifically sound if Adam did not lose a rib but instead his baculum.” Also – why publish this in the American Journal of Medical Genetics and why frame it as a genetic disease? I wish their commentary had been more explicit (but that may just be my passing the buck when I should have read more critically). Thanks again – any other thoughts most welcome.

  5. Okay, but your taking the authors literally is on the same leel as creationist taking the bible literally.

    The authors, when they say that it makes more sense to read the passage in Genesis as god took the baculum of Adam and formed Eve of it do not mean to say that they literally believe that themselves. They only say that it makes more sense than the English version including the mistranslation that god took a rib of Adam. They do not therefore themselves believe that god did take the baculum of Adam and did form Eve of it. they only claim that their interpretation is closer to the original (that is Hebrew) meaning of that passage of scripture (that is the Hebrew codex that was template for the Greek, and then Latin, and then English versions.

    It’s a historian’s eye view I guess. The idea of a historian is to understand a source in its own terms, time and context, but that understanding does not mean believing.

    By the way, I posted the whole passage where Dawkins is relishing in textual criticism in his The Selfish Gene at my blog: http://historiesofecology.blogspot.de/.

    • Jeremy Yoder says:

      Yeah, making an honest mistake, then using it as a jumping-off point for a factual discussion the factuality of which doesn’t actually hinge on the mistake, then cheerfully admitting and correcting the initial mistake … that’s exactly how creationists operate. They’re sneaky like that.

  6. noahmattoon says:

    Joachim, I think Sarah is agreeing with your first comment. To then imply that her level of sophistication is on par with that of biblical literalists is quite condescending. The letter is very strangely structured, opens with a statement that very strongly implies a poor understanding of evolution (there are genetic “diseases” that affect 100% of the human population?), and the repeated use of language such as this:

    “Our opinion is that Adam did not lose a rib in the creation of Eve… We think it is far more probable that it was Adam’s baculum that was removed in order to make Eve. That would explain why human males, of all the primates and most other mammals, did not have one.”

    very much overshadows the ambiguous phrasing implying that the authors are reading the text at a remove. This certainly led me to initially take the piece as either a creationist work or hilarious satire.

  7. Okay, excuse me. Maybe it is not possible to read such a piece without thinking of the creationists being behind it in the USA. I have to admit, that I fortunately do not have much experience with creationists of the ilk that Yeremy describes. But if they screw up the academic discourse in America to such an extent that you already have to suspect them behind academic journal articles, then that’s really bad. If I know it’s a peer reviewed article, I usually do not suspect creationist agendas. Excuse my sound level.

    • Hird says:

      Haha – yes! Unfortunately Creationists are everywhere over here! Although, you’re right, they’re usually not in peer-reviewed journals (but since this was a letter, I wasn’t sure how stringently it was reviewed).

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