Penis spines! (oh, and something about brains too…)

Posted on March 10, 2011


Nature‘s editors and authors tried, they really tried, titling the report published yesterday “Human-specific loss of regulatory DNA and the evolution of human-specific traits”.

But from the earliest news report I can find (yesterday on Science 2.0, titled “Why Your Penis Has no Spine”) through to the raft of articles today, reporters have had their vision firmly focused in one place.

Perhaps since I notably lack the structure in question, I was drawn to comment on the other major finding reported, which has to do with the lifting of a gene inhibiting cell division in the brain– not too important, since all it likely did was help lead to the modern human brain, with its densely packed cortical neurons surpassing those of all other animals.

But now let’s get back to the penis spines! As Science 2.0’s Hank Campbell boiled it down

So why did this non-coding region of DNA get deleted?   They say it is because humans became couples and adapted monogamous reproduction and morphological characteristics followed.   So your penis has no spine because of pairbonding and increased paternal care.  Thanks, wife!

Damned wives.

Of course, as University of Wisconsin anthropologist John Hawks explains, the evidence from living primates doesn’t support this explanation:

penile spines don’t always mean fast sex. Galagos have penises covered in long hook-like spines, which they use in virtual sex marathon sessions lasting two hours or more. Prosimians tend to have much more elaborated spines, in contrast chimpanzees’ spicules are comparatively minor — in a broad comparison across primates, Harcourt and Gardiner rated chimpanzees along with humans as having insignificant penile spinosity.

But never let it be said that science reporters let facts get in the way of a good storyline. I mean– penis spines! How cool would that be?

You can practically hear the heavy breathing in all these stories, but SyFy News wins for most offensive spin, writing that “Sex would be a very different, not to mention painful, proposition had man not evolved to lose spikes that once existed on the male penis.”

Perhaps the author of this report was confusing chimpanzees with domestic cats. It’s understandable: both are furry, both are smart, and both have spines on the penis. But only one of these species has spines that cause damage to the female with whom they mate.

To be fair, some news outlets managed to cover this research and not succumb to this particular sensationalism. CNN, for example, actually managed to report accurately that

speculation abounds about what purpose the spines serve. One theory is that they are used in sperm competition; if the male’s goal is to get his mate pregnant, he will want to take out her previous partner’s sperm if she’s recently had sex. The bumpy penis may be better for removing that sperm from the female, scientists theorize.

(Want a dense scholarly source for those theorizing scientists? Brace yourself and try this one.)

Would it be biased for me to note that CNN’s report is written by a woman– Elizabeth Landau? On Bloomberg News, another female reporter, Elizabeth Lopatto, manages to reconceive of the “spines” as a “ridged penis” that lets chimpanzee males complete copulation more quickly– what we might call the French tickler model.

Not that have a female reporter was a guarantee that coverage would be entirely accurate.

In an otherwise sober and reasonable summary of the research that gave due weight to the brain findings, Megan Scudellari of The Scientist implied the “sex would have been painful” argument by writing about “penile spines, which mice and other primates still have, but humans (thankfully) lack”, and even more by illustrating her story with a closeup of the spiny genitalia of a Callosobruchus analis beetle.

But that is nothing like the degree of emphasis on insects and other inappropriate animal models by Stephanie Pappas at LiveScience. And Jennifer Viegas at DiscoveryNews makes the bald assertion that chimpanzee penis spines “can inflict damage on females during intercourse”, something for which I have found no source.

And to give credit where credit is due, Ed Yong in Discover‘s Not Exactly Rocket Science blog made the key point missed by other outlets:

The spines aren’t there to inflict injuries … They’re hair-like and sensitive. Without them, sex is probably a less stimulating activity for human men than for other male mammals, and it takes relatively longer.

As I wrote in What Makes Us Human, “what we do with our brains seems far less fascinating to reporters than what males of our species no longer do with their genitalia”. But I pulled my punches on the conclusion to that post, thinking maybe Psychology Today was not the place to make my final observation quite so bluntly:

So maybe we haven’t advanced all that far, really, since we still seem to be thinking with our dicks instead of our brains.