Last spring, the journal Current Biology published a report describing something new under the entomological sun: A genus of tiny cave-dwelling insects, dubbed Neotrogla, in which females, not males, have penises.
Or, rather, the females have a thing that they stick inside the males. Once it’s in there, that thing inflates and latches into the male with tiny barbs, binding the couple together in a copulation lasting two to three days, while the thing collects a packet containing sperm and a whole lot of (potentially) nutritious protein. What to call the females’ thing seems to have puzzled even the scientists who described it. In the text of their paper, they call it a gynosome (literally, a “female body”); but in the title, it’s a “female penis.”
This synonymy went from confusing to controversial the moment it hit the popular science press, which almost uniformly chose to go penis-first. “Female insect uses spiky penis to take charge” read the headline in the prestigious journal Nature. “Meet the female insect with giant PENIS whose steamy sex sessions last 70 HOURS,” said the Daily Mirror, caps-locked emphasis sic. Most of the stories, even the Mirror’s, got around to using the word “gynosome” eventually, and many went into more detail about how the organ in question wasn’t really a penis as we know it. LiveScience noted it was “a complex organ composed of muscles, ducts, membranes and spikes,” before adding that its size, relative to the body of a Neotrogla female, was “the equivalent of a man who is 5 feet 9 inches (1.75 meters) tall having a penis about 9.8 inches (24.9 centimeters) long.”
Annalee Newitz, the editor of the science fiction-and-fact site io9.com, rapidly lost patience with this. “When was the last time you found a penis that grew spines, absorbed nutrients, remained erect for 75 hours, or allowed its owner to get pregnant?” she wrote in a column on the Neotrogla coverage:
When we deprive Neotrogla of her gynosome by calling it a penis, of course Neotrogla doesn’t care. But we fail to advance the scientific project, which is above all things dedicated to expanding people’s understanding of the world. Instead of learning that there are female bugs with sex organs that behave unlike anything in the human world, articles about a “female penis” reassure readers that nothing could ever exist that challenges the penis/vagina sexual system — nor the system of sexual selection that led to it.
On National Geographic’s Phenomena blog, Ed Yong responded to Newitz in a postscript to his own article about Neotrogla: “I absolutely agree with Newitz that cheap dick jokes are doing the topic a disservice,” he wrote. But he differed on the need to avoid calling the gynosome a “penis” at all costs:
In fact, there is a long tradition in anatomy of describing organs with almost metaphorical names. A snail’s foot is not remotely the same as a human’s foot, but they’re both muscular locomotive organs that are kinda on the bottom of the body. We call them both feet. An octopus radula is not a human tongue, but they’re both mobile things inside the mouth that perform feeding functions, so we call them both tongues. “Eye” gets used to refer to all manner of light-detecting organs regardless of huge differences in their anatomy, evolutionary history, physiology, because they all share the common theme of detecting light.
Yong conceded that the “cultural and social baggage” associated with penises — everything done by those of us who possess them to those of us who don’t — should make scientists and science journalists cautious about following the same “almost metaphorical” approach for describing and naming genitalia. Still, he held that it was entirely possible to call the gynosome a penis without erasing its unique place among the endless forms of the animal kingdom.
It could have been even worse. In an article posted at the online journal The Winnower, the authors of the Current Biology report made a far more unfortunate choice, describing Neotrogla as “transgender.” Whether insects have genders, and whether it’s remotely helpful to describe members of an insect species fulfilling the very sexual roles for which their anatomy is adapted using a term we apply to humans whose gender identities don’t match their physical bodies, are much easier questions to answer than what to call Neotrogla’s novel genitals. (It’s “no,” on both counts, by the way.) But the sheer range of pitfalls available in describing the reproductive process of this one insect genus is a nutshell illustration of the fundamental problem with scientific investigations of sex: no matter how hard we try to focus on the anatomical and behavioral diversity of other species, we always seem to end up gazing at our own navels.
These are the choppy waters in which any biologist must swim, if she wants to study or write about sex. Can you explain how creatures so unlike us that they don’t even have backbones come together to reproduce without making them sound like little slime-covered people in the process? Can you describe how the anatomy and behaviors of actual birds and bees differ from ours without reinforcing narrow ideas about what constitutes “normal” for human beings?
In Nature’s Nether Regions, Menno Schilthuizen doesn’t so much walk this line as tap-dance up and down it. The book’s subtitle What the Sex Lives of Bugs, Birds, and Beasts Tell us About Evolution, Biodiversity, and Ourselves, might be a bit ominous to a reader familiar with the many hazards of evolutionary hypothesizing about human behavior, but Schlithuizen’s chatty tour of animals’ sexual anatomy dodges them all. He does this, in large part, by devoting far more time and attention to the “evolution” and “biodiversity” than to “ourselves,” putting the rather pedestrian reproductive arrangements of Homo sapiens in their place amidst the baroque diversity of appendages, receptacles, secretions, and behaviors other animals employ to multiply their kinds.
As an appetizer: in the species of squid most commonly eaten as calamari, the male’s genitalia isn’t, strictly speaking, his penis. That term is more appropriate the specialized arm he uses to transfer packets of sperm onto the females’ body, where, given the right stimulus — associated with laying her eggs — the packets explosively propel sperm in the direction it needs to go. This has caused actual medical issues for humans eating the wrong arm of an under-cooked squid.
Much of Nature’s Nether Regions is given over to this kind of natural history, told with a mix of awe and glee. Schilthuizen has apparently never met a sex-related pun he didn’t like, and he deploys them in the midst of elegant explanations for some astoundingly convoluted alternatives to insert tab A into slot B. Many vignettes are illustrated with lovely line drawings of organisms and their naughty bits, which recall classic natural history texts — except that the illustrator has often added cheeky annotations, such as a top-down view of a firing cannon alongside the diagram of the squid’s explosive sperm packets.
As Schilthuizen notes, though, a book full of descriptions of quirky and alien mating systems would be a stamp collection — fun to peruse, but ultimately not very useful. The broader project of the book is to explain how the curiosities on display in its pages have come to be, and the answer to that question is, often, sexual selection. In a nutshell, the idea is that males invest less in any individual offspring, while females provision eggs and raise the kids — so, over time, male traits that maximize the number of opportunities to mate should become more common, and female traits that maximize the ability to select just the right sperm donor should also become more common.
In a study Schilthuizen identifies as a forerunner of modern research on genital evolution, Jonathan Waage demonstrated that hairs on the pensises of the jewelwing damselfly, Calopteryx maculata, scoop sperm out of a female’s reproductive tract. In fact, Waage found, a substantial portion of damselfly copulation is devoted to this clearing-out process. The damselfly penis is shaped not only by the need to deliver sperm, but by the need to remove the sperm of other males, maximizing the number of a females’ eggs that are fertilized by her most recent partner. In other damselfly species, there are counter-adaptations, female anatomy that circumvents sperm-scooping to maintain choice over paternity.
This sexual co-evolution is where popular and scholarly accounts of sexual selection can often run aground on the idea that a fundamental feature of male-ness is the subversion of females’ will. In fact, it isn’t. Many animal species mate and raise offspring in ways that don’t fit the roles assumed by sexual selection, and attempts to apply the coercive flavor of sexual selection theory to the male and female roles of plants have had mixed results at best. Schilthuizen’s view through the lens of sexual selection is, however, refreshingly clear-eyed. He explicitly disavows combative metaphors in the back-and-forth of male and female interaction — because, as he notes, they get in the way of scientific understanding:
Tempting and illustrative as it may be to speak of the “battle of the sexes,” “evolutionary arms races,” or “tug-of-war,” I will try to avoid this as much as possible. Not only because it taints the sex acts of these innocent animals with the uglier kinds of human aggression, but also because the comparison is faulty. In warring factions, the two groups that are in conflict with each other will always remain separate and every point score by a group member will benefit his clan only. Males and females are not to be confused with separate clans, for the simple reason that they spawn their own enemies: males also get daughters and females also get sons.
Elsewhere, Schilthuizen describes the use of chemical signals delivered in semen, which prompt the female reproductive tract to release eggs, or decrease females’ sex drive, or otherwise improve the odds that the sperm they accompany will have paternal priority. Other authors have often characterized these as manipulative adaptations in a kind of sexual “chemical warefare”, but as Schilthuizen points out, they may equally well be “chemical communication” between male and female. There is not (necessarily) any need to invoke male coercion to explain why a female fruit fly responds to seminal “sex peptides” by taking a break from mating for a while.
As an evolutionary biologist with a particular fondness for plants, I can resist the temptation to ding Nature’s Nether Regions for its focus on animals, which really reflects a broader division in evolutionary biology. And: under the definition used by Schilthuizen, what count as a flowering plant’s genitals? The stamen and pistil, or the hummingbird that carries pollen between them, or the nectaries that attract the hummingbird? Or all of the above?
I do, however, sometimes feel the absence of a broader ecological perspective — as much as their function may be expressed in the mating act, the evolutionary forces acting on genitals extend well beyond what happens between foreplay and afterglow. The long, prehensile penises of barnacles make an appearance early in the book, but there is no mention of the fact that barnacles in particularly wave-swept habitats grow shorter, more robust penises, the better to cope with tidal turbulence. For the rest of the animal kingdom, as for humans, when and where mating occurs can be as important as what parts are employed in the act.
Still, this sort of intersection between natural and sexual selection — which applies to an appendage that must fight the environment before it fulfills its procreative purpose? — is perhaps beyond the scope of the book. Certainly there is a logical arc to Nature’s Nether Regions as it is, which culminates in the truly alien practices of species which have no separate sexes, but which may yet have substantial interests in trading sperm, and in negotiating the priority that sperm receives. These include hermaphroditic slugs, who intertwine themselves while suspended on threads of mucus to exchange packets of sperm with elaborate appendages that emerge near their heads.
This very sight recently captivated Washington Post columnist John Kelly, who compared the experience of spotting slugs in copula on a retaining wall beside his driveway to watching grizzly bears or manta rays in the wild — with tongue only partially in cheek. Schilthuizen frankly acknowledges this human fascination with all things sexual, particularly those that suggest practices beyond our social mores, right at the start of Nature’s Nether Regions. But even as he exploits it, he upends the prurient appeal of a book about non-human genitals by showing how many, many more things there are on the face of the Earth than are dreamt of in your father’s old Playboy collection.
Schilthuizen, M. 2014. Nature’s Nether Regions. New York: Penguin. Google Books.
Liu, H., and E. Kubli. 2003. Sex-peptide is the molecular basis of the sperm effect in Drosophila melanogaster. Proc. Nat. Acad. Sci, 100(17): 9929-9933. doi: 10.1073/pnas.1631700100.
Neufeld, C.J., and A.R. Palmer. 2008. Precisely proportioned: intertidal barnacles alter penis form to suit coastal wave action. Proc. Royal Soc. B, 275(1638): 1081-1087. doi: 10.1098/rspb.2007.1760.
Waage, J.K. 1979. Dual function of the damselfly penis: sperm removal and transfer. Science, 203(4383): 916-918. doi: 10.1126/science.203.4383.916.
Yoshizawa, K., R.L. Ferreira, Y. Kamimura, and C. Lienhard. 2014. Female penis, male vagina, and their correlated evolution in a cave insect. Current Biology 24(9):1006–1010. doi: 10.1016/j.cub.2014.03.022.