Lliving organisms have been colonizing the planet for nearly four billion years. They have taken countless forms through various evolutionary and adaptive mechanisms to survive in an environment where conditions are extremely specific and constantly changing. One of the most striking features of animals that reproduce by internal fertilization is the morphological diversity of the genitals. It is noteworthy that in species with slight differences in overall morphology, there are significant differences between the genitals of males (which researchers paid more attention to than in females).
There seem to be several reasons for this impressive evolutionary development, and the unanswered questions are encouraging. What is the purpose of the penis? Why is it that members of one race have no penis at all while another has two? Why are they so different in shape and size? And where does the vagina or clit fit in all of this? What about the joy? Does such a thing exist in the animal kingdom at all? If so, what forms does it take?
The mechanisms involved are complex. To have any chance of understanding them, we need to look at how these organs evolved. This means going back more than 400 million years, long before dinosaurs traveled the earth. Up to this point, fertilization was essentially external: females ejected their eggs into the water and males with their semen. But when certain sea creatures emerged from the water, their bodies had to adapt to the new environment. Including the genitals: external fertilization does not work if males – and females – release their gametes into the air or the ground; the biological material does not live too long. Reproduction required a real innovation in anatomy so that life could flourish in the terra firm. This is where internal fertilization comes in: the female keeps the eggs in her body and the male adds his sperm.
There is fierce competition for the transmission of genes, both between individuals of the same sex and between males and females. As a result, different species have developed different reproductive strategies, from new organs to open war between the sexes, culminating in male self-sacrifice. The fauna holds countless surprises. Such strategies are rooted in striking differences in genital forms and functions.
The following are just a few of the most unlikely examples, at least by human standards, of how animals’ bodies, behaviors, and especially their genitals have adapted to meet their own reproductive needs in their own small slots.
THE WATERCRAFT (Micronecta scholtzi)
The water boat is a two-millimeter insect that is common in freshwater lakes across Europe. Unpretentious in every way – except one. Males of this species are attracted to females by singing. All right, you could say they’re not the only ones doing that. True, but these gentlemen do it with their penis. A sounding penis? Yes really. Males rub their organs against the rough spine of their bellies to produce a strong chirp that attracts females. This is sometimes called a “singing penis”. Quite charming. But let’s not rush to draw conclusions about the origin of the song in the male sexual apparatus.
Attracting females to water is a serious problem: the wavelength of sound in this element is long. In order for a potential partner to hear anything, pair calls need to reach a high volume to increase the range of the signal transmission. However, the body size of these insects is limited and there is a risk of attracting predators. This is why male crickets and boaters use resonance structures that produce songs specific to each species at a volume appropriate to their physical size that predators cannot pick up.
Despite their small stature, these tiny insects can really surround you. Their “singing penis” may be only 50 microns long, but they keep the record in terms of the volume emitted by insects. This is the loudest penis in the world! The beep sound can reach 99 decibels. If you don’t know what to do with this figure, it’s as loud as if you’re listening to a band from the front row. As a reference, when an elephant plays its trumpet, it’s just over 110 decibels – but an elephant is more than 2,500 times as big. Obviously, our little bug is the most efficient noise generator in terms of acoustic energy relative to size in the entire wild realm.
Even more compelling is why such a powerful song was created, it’s still a mystery, and the exact mechanism of action remains unclear. We need to do more research in the aquatic environment, especially on how the acoustic behavior and anatomy of these creatures have adapted to that environment. The intensity of their singing is considered a secondary sex characteristic that appears at the beginning of puberty – for example, the antlers of deer, the singing of some birds, or the color of any number of animals change. In light of this, we can assume that the boatman’s song responds to strong mating pressure among males: competition prevails during courtship. The most winning voice seduces one or more partners. We need to do more work to find out how females value the relative attractiveness of a singing penis. Does size matter – that is, volume?
THE GRASS (Syntonarcha iriastis)
The water boat is not the only animal to have a male member equipped with a sound system. Take the lawn butterfly, a small insect of Indo-Australian origin. Males sit on trees and bushes, spreading their wings and freeing their genitals. It is clear that this exhibitionist visualization — their reproductive organs include files, scrapers, and resonant zones — among others — employs a mechanism that causes ultrasound frequencies. The researchers used a device originally designed for bats to detect sounds from a distance of twenty meters. Needless to say, one assumes ladies are being called for mating.
But it is possible that these songs have a completely different function. Some of them are very similar to the echolocation outbursts used by insectivorous bats to find prey. Researchers have no doubt that imitating the sounds made by bats is a gimmick. The exact purpose of this is more mysterious. Does it happen that the female, sensing the approach of the predator, freezes and stays there – making it available to the suitors? Not excluded.
Another hypothesis is that the sounds made by the butterfly serve to confuse the sonar of the bats, making it difficult for them to find prey. At one time, I refused to believe that genital noise could be used to send predators the wrong way. But now nothing surprising is happening in the animal kingdom – especially since there is no evidence that females of the species are attracted to these ultrasound transmissions at all.
Finally, scientists have proposed a third hypothesis that has been developed by studying the yellow peach moth (Conogethes punctiferalis). This time, the issue is competition between men. They seem to be able to chase their rivals with a series of short impulses and enchant the females with persistent voices. The staccato release is really similar to the sounds of bats, while the long sounds make interested ladies lift their wings as a sign of greeting. Dulce et utileas classical wisdom would say.
FOSSA (Cryptoprocta ferox)
The 25-pound predator associated with the mango is the largest predator in Fossa Madagascar. Primatologists know the creature as one of the main predators of lemurs. Like lemurs, fossils are threatened by a dramatic decline in biodiversity on the island they inhabit. But that is not why I am mentioning these magnificent animals here; what interests me is their extraordinary sexual adaptation. The fossa is one of the rare mammals in which females, while still immature, go through a passing phase of masculinity. What is this, you ask? For a time, they think of others as men. This trick is very practical for communicating false information and thus ensuring females ’own safety. So how do they do it and from whom – or what – do they protect themselves from?
In this phase, the clitoris grows; then spines develop in the extended organ that look as if the species belongs to an adult male. Girls seem to adorn themselves with this feature to avoid aggression from guys looking to mate; the prickly clitoris is deterrent. In short, transient masculinisation allows young females to avoid sexual harassment and improve their chances of survival. Unwanted attention from males can eventually lead to injury or even death. The fact that adult females are not always nearby and the annual oestrus cycle does not last long causes males to mate quickly and often – hence their aggressive behavior. Young females are particularly vulnerable as they are small and have just left their homes. Camouflage induced by clitoral transformation allows them to avoid detecting males. In addition, such genitals are an obstacle to cooperation. A very radical solution!
At the same time, masculinization serves to protect juvenile cavities from same-sex men. The danger is everywhere. While males appear to be somewhat territorial — data from radio tracing are limited — mature females have areas that they consider completely their own. At an age when they are just beginning to leave their homes, young ladies have yet to find a place in the world and are risking unfortunate encounters with older females. An enlarged clitoris helps avoid confrontation.
Whatever the reason for the morphological and behavioral differences in animal sexuality, they certainly exist. The most widely accepted theory is that different reproductive organs have evolved to prevent the mating of different species; nevertheless, such a precaution seems unnecessary, since the encounter of different animals, if at all, only produces sterile offspring.
In any case, diversity clearly flourishes at all levels: social interaction between men and women (competition, monogamy, multiple partners), ways of seduction (building a pergola, giving gifts, new coats or feathers, tricks), parade techniques (dancing, singing), mating (on the ground, in flight, in various positions), and placement and conditions (outdoors, in the woods, near or away from predators). There is therefore no reason why morphology should not show similar differences. Nothing is set in stone. Human beings have not invented anything new. Humility is appropriate here. “Sex diversity” existed long before we appeared. As always in the animal world, no matter which side it is in, the world of discovery awaits.
This essay is from the book Sexus Animalis: There is nothing unnatural in nature. Copyright © 2022, Emmanuelle Pouydebat, translated by Erik Butler. Used with permission from the publisher, MIT Press.
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