Zoobiquity (11 page)

When the erection is complete, and stimulation has reached what doctors poetically if vaguely describe as the “
point of no return,” a spinal cord reflex causes a sudden burst of muscle contractions throughout the genital area, starting with the neck of the bladder. In rippling chains of contractions fueled by massive outflow from the sympathetic nervous system, the muscles around the testes and scrotum tense, followed by those of the epididymis, vas deferens, seminal vesicles, prostate gland, urethra, penis, and anal sphincter. The rapid clamping and unclamping of these muscles, at intervals less than a second apart, spurts semen out of the urethra. A few slower spasms may follow that initial explosion of muscle activity. This sequence has been preserved across a wide spectrum of mammalian species.

The comparative study of ejaculation has focused mostly on primates and rodents.
But all male mammals descend from shared ancestral ejaculators. The penises of mammals from narwhals to marmosets to kangaroos propel semen in nearly identical ways.
And the ejaculation of a male human today even shares basic physiology with reptiles, amphibians, and sharks and rays. Ejaculation isn’t new. In fact, the human seminal propulsion system has ancient origins. This makes it not only intriguing but plausible that the human male’s experience of ejaculation may be shared by other animals. With the mechanics being so similar, the question is, do other animals experience the intense pleasure that drives so many men to such good and bad behavior?

The experience of orgasm is not only legendary but also measurable.
Electroencephalograms show brain-wave shifts, including an increase in slow-frequency theta waves, which are associated with deep relaxation.
Many men describe a feeling of euphoria intriguingly similar to what heroin users describe experiencing when they plunge a needle into
a blood vessel and discharge the drug into their system. The brains of ejaculating male rats are known to release powerful chemicals, including heroin-related opioids, oxytocin, and vasopressin. Taken together, the muscle contractions, brain changes, chemical rewards, and relaxed feelings add up to create the male orgasm.

After ejaculation and orgasm, a process called detumescence, or deflating, begins. Neurohormonally, this sequence is essentially simply the reverse of erection. The smooth muscle of the penis shaft contracts. So do the penile arteries. Blood flow to the penis decreases. With less pressure pushing them shut, the veins open up and normal drainage resumes. Chemicals associated with the sympathetic nervous system begin to take over. And before you know it, the penis is back in its resting state of slight contraction.

Clearly, a lot has to happen for this amazing structure to build on cue. But with that many dependent steps, a lot can go wrong. To complicate matters, human erections can be achieved in essentially two ways: through thought or through touch.

As most men can attest, the penis is perfectly capable of achieving an erection purely from direct stimulation. It’s called a reflexogenic erection and is regulated by nerves in the lower spine. Reflexogenic erections are well known to prepubescent boys, men in deep states of REM sleep, and men with spinal cord injuries (in whom the nerves connecting brain to penis have been severed). Reflexogenic erections are as unconsciously controlled as digesting and breathing; they can spring up when a man least suspects or wants them.
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Reflexogenic, early-model proto-erections, in species such as barnacles and mollusks, evolved long before reptilian or mammalian penile stiffening. While effective at penetration and sperm delivery, these erection 1.0s lacked what more evolved erections offer: opportunistic engorgement and strategic deflation.

An important advancement in the evolution of erection was the addition of input from the brain. This allowed the brain to send signals to the
penis through the spinal cord. From an evolutionary perspective, these psychogenic or “cerebrally elicited” erections are a savvy improvement on the reflexogenic type. Involving the brain in a process as intricate and crucial as an erection expands the animal’s reproductive opportunities and physical safety. It allows him to judge and respond to his environment before firing up or shutting down an erection. It enables sensory inputs like seeing, smelling, touching, or even thinking (fantasizing) about someone or something sexy to trigger the erection cascade. And it facilitates nearly instantaneous shutdown when a predator—or, more likely, a competitor—reveals himself.

And this is true whether the male is a moose, a mole, or a man.

My tour of the U.C. Davis horse barn included a visit to a small white room about the size of a galley kitchen in a New York City apartment. Where a Viking range might have been, a high-tech, semen-spinning machine stood instead. Nearby was a refrigerator-freezer, for storing ejaculate and frozen urine. The urine, as I’d seen in the breeding shed, plays an essential role in the sensory stimulation leading to psychogenic erection.

When a randy stallion walks past a mare who’s in heat, she will often instantly, reflexively let loose a steaming stream of urine. This serves a strategic purpose. Urine contains telltale molecules that indicate a female’s ovulatory status. When women buy a box of plastic ovulation-predictor sticks, they are purchasing fertility-detection technology that a stallion’s nostrils can provide for free.

Male horses (along with many other animals, including camel, deer, rodents, cats, and even elephants) can detect these compounds by sniffing and tasting urine. Their sense of smell is enhanced by a characteristic grimace they make called a “flehmen.” This one-sided lift of the upper lip resembles an animal version of Elvis Presley’s famous sexy sneer. As the animal raises his lip, he inhales, wafting the odor molecules into contact with his vomeronasal organ, a sensitive scent detector located near the roof of the mouth. Humans perform a similar chemoreception when they slurp and swirl wine around the roof of the mouth to bring the aromatic molecules in closer contact with the sensitive receptors in their gums and nostrils. Whether or not we once had a vomeronasal
organ is up for debate. Some biologists believe humans have lost it; others question whether we ever had one.

What we
do
continue to share with animals that possess a vomeronasal organ—and perform the flehmen grimace—is the seventh cranial nerve.
Also called the facial nerve, this brain-body communication line runs between the face and the emotional centers of the brain. This same nerve, originating in essentially the same place in the brainstems of many animals and all humans, transforms anger into a dog’s snarl, surprise into a macaque’s widened eyes, and joy into a child’s smile.
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If you picture a human doing a flehmen, you’ll notice something unmistakable. The single-sided, upturned lip is also an instantly recognizable expression of disgust. If you try it yourself, you might even feel a little ripple of repulsion. Yet a pantheon of sexy male rock stars—from a strutting Mick Jagger to a sneering Billy Idol—has exploited this ancient multitasking neural circuit to flash-flehmen their female audiences, with swoon-inducing effects. Elvis’s ancient lip curl, perhaps more so than his swinging pelvis, sent adolescent girls into shuddering seizures of excitement and ecstasy. Having seen what a stallion’s flehmen indicates to a receptive mare, I can understand why Elvis’s blatant sexuality may have threatened a whole generation of fathers in the 1950s.

That the flehmen signals both lust and disgust is thanks to the intertwining anatomic connections with the brainstem. And it may help explain why so much about our genital and urinary functions both fascinates and repels us. Male urine can communicate chemically to females as well as the other way around.
Male porcupines court females by showering them with urine during precopulatory courtship.
Male goats spray urine on their faces and trademark billy-goat beards as an olfactory indication of their sexual readiness.
Elk bucks similarly wallow in urine during rutting seasons.

Nonmammals communicate using urine, too.
Courting female crayfish release a stream that attracts interested males.
The urine of male swordtail fish is full of pheromones. Males swim upstream and then urinate,
so that the sex-communicating liquid flows downstream, where it can be “read” by available females.
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When Lancelot was led past the fertile mare, he was allowed to look at her but not touch. Surely part of her effect was olfactory. In addition, the sight of her raised tail would have been a visual invitation. Sight cues are another very powerful stimulant of psychogenic erection. Visual cues—we might call them nature’s pornography—excite many animals.

For example, the reddening and swelling of the female genital area (called perineal “elaboration”) shown by many monkeys and apes signal that they are ready to mate. Males of these various species respond to the size of the swellings and are most visually excited by the largest ones.

Blindfolded bulls in a test situation were much less likely to mate with an unfamiliar cow than bulls that could see. Restricted vision impaired the bulls’ performance.

Visual stimulation has an interesting effect on females, too. Male courtship displays are the iconic stock images of nature documentaries, from mighty rams butting heads to gentle bowerbirds presenting their paramours with nests intricately inlaid with flowers, shells, stones, and berries. The reason for all this visual excitement is to entice a female into copulation—by communicating not just sexual readiness but superior genetic fitness. However, these displays might also have an invisible effect that extends beyond the act of copulation and actually improves survival of any offspring.

Researchers in Morocco were desperately trying to improve the reproduction rates of an endangered bird called the houbara bustard. These natives of northern Africa have been hunted into near oblivion for their supposedly aphrodisiac meat. After the artificial breeding program had produced disappointing hatch rates, investigators realized that some of the females they were inseminating by hand had never actually seen a mature male bustard. So they decided to try an experiment. Instead of simply placing a sample of sperm into the females, they first gave them a look at a sexy male bustard—one who was strutting around in the
characteristic houbara pre-mating ritual, with his white head and neck feathers puffed out like a rock star wearing a boa. Females who had been primed with this sight—no matter whose sperm they were eventually fertilized with—were more likely to lay viable eggs. Their chicks were more likely to hatch and were stronger when they did. The reason: primed with the sexy sight, the females added more testosterone to their eggs. This made them grow faster and stronger. It spurred the chicks to create more testosterone on their own, giving them a hormonal head start in life. Of course, this was not a conscious choice the mother birds made; rather, it was a physiological response to a visual cue.
Similarly, pig breeders have found that sows who were “courted” by boars before artificial insemination—or even just exposed to boar odor—had higher conception rates.

In the animal world, females are not just passive vessels receiving sperm but active participants who can influence the outcome of their breedings through sperm selection and egg enhancement. This is a new area of study that could have important implications for improving animal breeding programs around the world. And it could also help women struggling with infertility. Assisted reproduction has come a long way in the past decade, but although the male specimen-collection rooms of fertility clinics are well stocked with racy magazines, women are not regularly advised to be “visually motivated” during monthly egg development. Maybe surfing YouTube for clips of a drenched and brooding Colin Firth, riding crop in hand, would have an enhancing effect on egg recruitment and growth, whether a woman is going through in vitro fertilization (IVF) or trying naturally for conception.

Yet another brain-based erection enhancer enters male brains through the ears. Canoodling horses nicker and whinny; in-the-mood boars “chant.” The biologist Bruce Bagemihl notes that “
female Kob antelope whistle, male Gorillas pant, female Roufous Rat Kangaroos growl, male Blackbuck antelopes bark, female Koalas bellow, male Ocellated Antbirds carol, female Squirrel Monkeys purr and male Lions moan and hum.” Any one of those sounds, produced for a willing recipient, could trigger a neural cascade that would result in or enhance an erection.
One fascinating study revealed that female Barbary macaques timed their “loud and distinctive” copulatory utterances to coincide with—or perhaps influence the likelihood of—their mate’s ejaculation.
Bulls have been found to get erections when played a recording of the sounds of a cow in estrus.

But the brain’s ability to translate sensory inputs into an erection has a deflating flip side. Sometimes, instead of encouraging an erection, the brain squelches it.

A mating animal is vulnerable. It’s necessarily distracted from its environment. It’s momentarily disconnected from other important survival activities, like food gathering and territory defense. A psychogenic component to erection means that if a male’s brain detects danger, threat, competition, or diminishing returns, it can terminate the erection.

But this physiology sets the stage for the number one reason human males visit doctors with sexual complaints: erectile dysfunction, or ED.
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That’s when erections consistently don’t achieve the hardness required for penetration or last as long as they once did. Although not life-threatening, as medical problems go, ED can profoundly affect quality of life and the social well-being of men and their partners.
Worldwide, one in ten men suffers from ED, thirty million of them in the United States alone. Preoccupation with penile stiffness sustains a multibillion-dollar industry that peddles drugs, devices, dietary aids … and not a small amount of snake oil.

According to Arthur L. Burnett, an expert in neurourology at Johns Hopkins University, our understanding of erectile dysfunction has done “an about-face” in the past four decades. Doctors used to think ED developed out of inevitable yet vague factors like aging and hormonal imbalances—or that it was entirely psychological. In the heyday of psychoanalysis, a man’s inability to achieve a firm erection was presumed to be a consequence of his unresolved internal conflicts.