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. c
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 thepenis 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
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. c
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 thepenis 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
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