Zoobiquity (10 page)

Experienced horse breeders like Viloria know that even very practiced stallions sometimes can’t perform sexually. As one website counsels, “
Most people think of stallions as being big and tough, but they actually are quite sensitive. Circumstances have to be to their liking for them to feel comfortable with breeding.”

Even when copulating with a live mare instead of producing a semen sample for artificial insemination, stallions can suffer from stage fright, intimidation, distraction, and inexperience. Male horses who are punished for sexual behaviors by rough handlers or mean mares in their youth may develop inhibitions around mounting and copulation as adults.
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Some stallions show sexual interest in mares but will not mount. Some will mount but will not penetrate. Others get through the first
two stages but cannot ejaculate. And there are stallions who will mount mares only when another particular horse is present or watching. Among some social animals, including horses, the highest-ranking males dominate mating. The runners-up are deprived of most sexual opportunities.
Their lower status and forced celibacy put them at risk for what veterinarians call “psychological castration,” the eventual inability to have sex at all.

As Jessica Jahiel, an author and expert in the fields of horses and horsemanship, writes, “
Pain, fear, and confusion can all lead to vastly decreased libido and sometimes an inability to breed.”

Like veterinarians, human physicians also encounter patients in whom fear, pain, and confusion (and many other factors) interfere with the ability to have erections. As medical students we’re taught to ask every patient about their sexual function and satisfaction, and we know we should because sexual performance is a useful measure of cardiovascular fitness. But the truth is that many doctors find it easier to ask Mr. Green whether he can walk up two flights of stairs without symptoms than whether he has chest pain during intercourse. Unless a patient brings up a specific sexual problem during a visit, physicians aren’t likely to inquire about the quality and frequency of a patient’s erections, ejaculations, and orgasms.

Cultural barriers, time constraints, and even prudishness get in the way of in-depth discussions about sex between physicians and patients. So, while a patient’s sex life contains key information about his or her overall health, most physicians will address only those sexual problems that a patient feels need fixing.

Veterinarians, on the other hand, see and deal with sex much more as a normal part of their patients’ lives. The first time I attended morning rounds at the Los Angeles Zoo, I was surprised by the careful attention the vets and keepers paid to the sexual activity of the animals in their care. How much, how often, and with whom—it was all valuable information relating to the physical and mental well-being of their patients. And the discussions proceeded without the uncomfortable silences and flushed faces I’ve seen in human exam rooms.

Spend any time around animals and you’ll notice that
sex comes in many forms. Some species commit to monogamous lifelong partnerships. Others are outrageously promiscuous and spread sexually transmitted diseases (STDs). There are species that engage in heterosexual
behavior at one phase of their life and homosexuality during another. There are animals who rape, animals who trick partners into sex, animals who force themselves on their young. There are also animals who engage in what appears to be lengthy foreplay. Animals who fellate their partners. Animals who secure a form of consent before engaging in intercourse.

Careful scientific scrutiny of the shared biology and behavior of animal sex sheds light on the evolutionary background of human sexuality. A zoobiquitous survey of animal erections, copulations, ejaculations, and even orgasms could advance the treatment of human sexual dysfunction. And it might even uncover ways to enhance our sexual pleasures.

In this chapter we’ll journey through a world of insect foreplay, comparative clitorology, and the shared pleasure of orgasm. But there’s no better place to start this tour of the sex lives of animals, both human and nonhuman, than with the extraordinary feat of biomechanical engineering called the male penile erection.

Not surprisingly, when physicians study penises, we tend to focus on the human variety. But our world is abristle with phalluses and has been for at least half a billion years. Today and every day since at least the early Paleozoic era, in meadows, oceans, streams, and the air, many trillions of erections preceded trillions of copulations, which preceded trillions of ejaculations. Some erections sprouted readily and penetrated easily. Others flickered to life and abruptly terminated. Some were measurable in yards. Others were microscopic. Some were stiffened by blood; others by a similar fluid called hemolymph; others by skeletal supports made of cartilage or bone. Some erections culminated in mere seconds; others lasted hours.

It wasn’t always this way.
The earliest single-celled organisms on Earth simply cloned themselves. Some of their descendants still do. But as complex multicelled organisms evolved and eventually “discovered” the ability to mix their gametes, they gained a giant genetic advantage. (For more on this, see
Chapter 10
, “The Koala and the Clap.”) Since these ancient creatures lived in the sea, the earliest sex was a straightforward process of spraying sperm and eggs into the water. The lucky few connected.

In that massive free-for-all, the fittest sperm reached the eggs and were rewarded with the prize of bringing their DNA into natural selection’s next round. Sometimes the fittest sperm were the strongest swimmers. Sometimes they were the ones deposited nearest the eggs. Others developed ways to follow molecular scent pathways to find the eggs. Or they bundled together in teams to improve their timing and accuracy. As sperm perfected ingenious rudders, tails, chemical markers, and swimming strategies, the genital hardware that ejected them was evolving, too.

One innovation was internal fertilization, which allowed males to place their sperm not only near females but right inside them, next to the eggs. This allowed both males and females a measure of control over their offspring’s DNA. Females could audition males before allowing them to mate. Sperm was less likely to be spilled on barren ground. And one invention that effectively accomplished this combination of choice and precision was the penis.
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The oldest penis on record goes back 425 million years. It belonged to a crustacean found preserved under ancient volcanic ash at the bottom of a sea that used to cover Herefordshire, in England. The paleontologists who found the shrimplike creature named it
Colymbosathon ecplecticos
, from the Greek for “astounding swimmer with a large penis.”
Before it was found, the oldest known phallus was 400 million years old. It belonged to a fossilized daddy longlegs from Scotland.

When dinosaurs roamed the ur-continent of Pangaea about 200 million years later, their penises roamed with them.
Paleontologists have speculated about dinosaurs’ mating apparatuses and behaviors, using what they know of crocodilians and birds, today’s relatives of those prehistoric creatures. The erect penis of a male titanosaur, for example, may have been twelve feet in length. Experts speculate that the male sauropod, with a body the length of a school bus, approached the massive, receptive female from behind. Like his crocodilian and avian descendants,
he likely inserted his penis from this dorsal position and, at climax, ejaculated sperm through a vessel running along the outside of his organ.

Nowadays, Earth’s penises exist in multivaried splendor.
Spiny anteaters sport four-headed varieties that rotate between copulations. Although most birds don’t have penises,
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the phalluses of Argentine lake ducks are nearly eight inches long (almost as long as an ostrich’s), corkscrew-shaped, and festooned with dense, brushy spines that sharpen to hard spikes at the base.
Despite a thirty-three-inch member and a penis-to-body ratio of seven to one,
Limax redii
, a Swiss slug, doesn’t have the most impressive proportions in nature.
That title goes to
Balanus glandula
, which wows the tide pool with its prodigious barnacle penis.
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Permanently cemented to a tidal rock, the barnacle sports a penis forty times the size of its body. Barnacle penises, as long as they are, vary in their girth. Barnacles living in rougher waters sport thicker, stronger, and sturdier members. But those in calmer surroundings extend their longer filamentous penises in search of distant barnacle “vaginas.”

Fleas and some worms also have hugely proportioned penises. And some animals have more than one.
Several species of marine flatworms have dozens of penises.
Some snakes and lizards are doubly endowed; switching between their two hemipenes during multiple copulations increases their sperm count by a factor of five.
As for insects, so exuberantly inventive are their male genitalia that entomologists scrutinize them to classify entire species.

If you haven’t thought much about the procreative thrustings of other animals, especially those you can’t see, you’re not alone. Many animals are nocturnal, extremely small, shy, or just very careful to mate where other animals (including curious biologists) can’t see them. Inaccessibility to these covert proceedings has been a barrier to the comparative study of sexuality.
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But the challenges of achieving up-close analyses of
these animals in flagrante delicto have meant gaps in knowledge and frank misinformation.

The sexcapades of krill, for example, have been seriously underestimated. These tiny shrimplike creatures make up the bulk of the diets of important aquatic megafauna, including whales. It had long been assumed that krill reproduce by mixing their eggs and sperm near the surface of the water. In 2011, however, the journal
Plankton Research
reported the surprising discovery that Atlantic krill—all 500 million
tons
of them—mate at depth. In these deep, dark, underwater orgies, krill use internal fertilization techniques that involve penetrative sex.

Since arising more than 200 million years ago, all male mammals have had penises, each achieving erection in one of three ways.
An actual penis bone, called a baculum, offers a stiffening assist to many male bats, rodents, carnivores, and most nonhuman primates.
A rope of thick tissue running down the center of the shaft partially stiffens the fibro-elastic penises of pigs, cattle, and whales. (The popular chew toy sold in pet stores called a bully stick is made by drying out this bull penis structure.)

But humans, along with armadillos and horses (not to mention several nonmammals like turtles, snakes, lizards, and some birds), have what’s called an inflatable penis. These organs thicken and harden using only hydraulics and internal compartments of spongy tissue that fill up with blood or other body fluids.

From a biomechanical perspective, these inflatable kinds of penises are really quite extraordinary.
As Diane A. Kelly, a biologist and penis expert at the University of Massachusetts, Amherst, explained to me, creating a structure adequately stiff for penetration that is also strong enough to withstand intravaginal thrusting is a tricky mechanical challenge. The steps that go into building a hard penis have an elegant flow that would please any professor of engineering.

It starts with the deceptively inert, flaccid penis. A penis in repose,
although it seems floppy and relaxed, is actually in a state of constant, moderate contraction. The tube of smooth muscle that runs down its center is mildly tensed. So are the linings of the thousands of tiny blood vessels that crisscross the organ. Further contraction of this muscle and the arteries is what accounts for shrinkage in cold weather or water. So although a penis in the process of erecting can seem like it’s springing into action, it’s actually submitting to a crucial, and opposite, process. First it must relax.

The command to relax comes from the pudendal nerves. When the smooth muscle lets go, arteries deep in the penis dilate. The channels suddenly open up. Blood rushes in, straightening the vessels and filling millions of tiny pockets in the two tubes of spongy tissue (called corpus cavernosum) that run the length of the penis shaft.

Next comes a key chemical reaction. When arteries dilate anywhere in your body—whether in your cheeks when you blush, your gut when you eat, or your genitals when aroused—they release nitric oxide.
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In the penis, this very special molecule (not to be confused with nitrous oxide, your dentist’s laughing gas, or nitrogen dioxide, the air pollutant) signals the smooth muscles to relax even further. More blood rushes in. By this point, the penis is crowded with liquid, and the increased volume compresses nearby veins, blocking their blood from flowing back out again. The chamber becomes tenser and tenser with trapped liquid, assisted by other structures that tighten and constrict. Pressure soars inside the fleshy tube. Most erections reach an internal pressure of one hundred millimeters of mercury—comparable to that which a boa constrictor might use to suffocate its prey.

To protect the organ from rupturing under this intense force, a complex net of collagen fibers surrounds the outside of the penis, under the skin. As Kelly describes, the collagen strands are arranged in deeply folded, alternating perpendicular layers along the length of the penis. This allows them to pleat open efficiently when the erection is under way. Not only does this collagen “skeleton” strengthen the erection, it gives the structure a resistance to bending that engineers call “flexural stiffness.”
(
Kelly says it’s a trick shared by pufferfish, whose expandable skin also contains highly crimped, alternating strands of collagen.) When the penis is not being used for copulating or mating displays, the erective construction has the added benefit of folding away for neat storage. Being able to stow your penis provides more than simple convenience.
A study on certain fish that cannot retract their reproductive organs—because they’re modified, permanently stiffened anal fins—showed that males with longer ones suffered higher rates of predation than those with organs that were less obviously on display.