10 Things You Never Knew About The Biology Of Sex

As the single most important act for the survival of our species, you’d think sex would be easier. Most of the time, it’s a simple guessing game of figuring out what goes where, but anything more complicated than that lurks like a hideously promiscuous elephant on a slippery slope of darkness and contrition. The truth is, for something we’ve been doing since the dawn of time, we just don’t know much about sex—but we’re learning. And we’re doing it the only way we know how—in a sterile lab, in front of scientists.

10 Arousal And Disgust

Sex is an innately disgusting thing. Copious body fluids aside, the mere act of sex is something we would never do if pleasure wasn’t involved. That may be one of the reasons arousal actually inhibits feelings of disgust.

“Disgust-induced avoidance” is the scientific term for not wanting to do something gross, like hesitating to drink a glass of water with a large fly floating in it. Normally, you wouldn’t even think about it. When you’re aroused, though, it’s more likely that you won’t care and take a big gulp anyway. In a recent study, 90 women were split into three groups: aroused, unaroused, and neutral. Then they were given 16 different tasks that ranged from “disgusting” to “more disgusting”—wiping their hands with a used tissue, reaching into a bucket of used condoms, and yes, drinking from a glass with a dead bug in it.

In reality, the bug was fake, and the condoms weren’t actually used—but the participants didn’t know that. The aroused women were overwhelmingly more likely to follow through with the tasks than any of the other groups, especially if the “disgusting” task was sexual in nature, like the condom bucket or putting lubrication on a vibrator. This suggests that inhibiting disgust is an important part of making people actually want to have sex.

9 Transient Global Amnesia

Transient global amnesia is a condition in which a person’s memory randomly disappears for a short amount of time. It happens suddenly and usually it goes away after only a few hours—but during that time, you can’t remember anything past a certain point. It also affects your ability to make new memories, so you’re constantly living inside a window of just a few seconds between doing something and forgetting about it. It’s like Memento, but without all the tattoos.

Since it’s so rare—only about three people out of 100,000 get it every year—doctors don’t really know what causes it, but one similarity has been popping up regularly since it was first recorded in 1956. In most cases, the person was having sex right before their memory goes blank.

Beyond the inability to remember anything, there aren’t any other side effects to transient global amnesia, but that doesn’t make it any less frightening. In a case from 1964, a man had an orgasm, then immediately shouted, “Where am I?” In reports where the person wasn’t having sex at the time of the attack, the trigger was usually something similar—strenuous activity of some sort, or a sudden change in body temperature.

8 Hot Women And Health

When you do something dangerous, like skydiving, your body pumps out massively increased levels of a stress hormone called cortisol. Cortisol is the primary hormone in the “fight or flight” response that floods your system with adrenaline and primes your body for survival. Put an attractive woman in a room with a man, however, and that man’s body suddenly can’t tell the difference between a nice set of legs and a rampaging bear.

In fact, just being alone with a beautiful woman for five minutes raises cortisol nearly to heart attack levels. It sounds like something you’d see in an old Tom & Jerry cartoon, but when Spanish researchers tested male hormone levels with a saliva swab after solo contact with an attractive female, their cortisol was actually right around the levels you’d expect to see after skydiving. The more attractive he thought the female was, the higher his cortisol levels rose.

They came to the conclusion that, like fighting off a predator, sexual interest is seen at the hormonal level as a challenge to be overcome. The more dangerous (attractive) the predator (woman), the more prepared he needs to be to survive (get laid). But there’s a catch-22: Women are actually turned off by men with higher stress levels. Sorry, guys. You just can’t win.

7 Orgasmic Exercise

Getting to the gym is hard for a lot of people. It’s a commitment, and one that comes at the expense of other, more enjoyable things—like virtually anything else. But for 5 percent of women, there might be a new reason to start working out: exercise-induced orgasms. It’s exactly what it sounds like—women have reported reaching climax simply from working out. The phenomenon was first mentioned in 1953 during an unrelated sex study by Dr. Alfred Kinsey, who said that a small percentage of the 6,000 women he interviewed voluntarily mentioned that sometimes their workouts came with some extra motivation.

A more recent study found that closer to 15 percent of women have experienced the phenomenon, and twice as many get at least some kind sexual pleasure. Granted, the “study” was an online survey without a whole lot of scientific control, but it does seem to be a fairly widespread issue. There’s even a name for it—“coregasm,” since most of the time, it’s triggered by abdominal exercises. It’s female-exclusive, as far as anybody can tell—sorry again, guys.

6 Zero-Gravity Sex

With several planned Mars missions just around the corner—some of which expect to put the astronauts and their families in zero-G conditions for more than 500 days—someone has to come out and ask the question that’s on everybody’s mind: “Can we do it in space?”

The answer is tricky, and NASA has already tackled it several times. As far as they’re willing to admit, nobody’s ever tried it, but the logistics would be something approaching rocket science. One expert put it in terms anybody could understand: “You have no traction and you keep bumping against the walls.” Or as Newton would have said, every thrust has an equal and opposite counter-thrust. Then there’s the problem of biology—sperm has never been asked to perform outside of normal gravity. In microgravity it would just ricochet around the uterus, bouncing off the walls like the kids in Ender’s Game.

Finally, there’s the small matter of what the radiation would do to a fetus if the hurdles of conception were ever overcome. We’re already unsure what the effects of long-term solar radiation would be on an adult, let alone a developing fetus.

5 Boosts Immune System

When you get a cold, your first reaction probably isn’t to kick yourself for not having more sex. From a physical standpoint, sex is healthy for you—after all, it’s just another form of exercise—but it also benefits you at the cellular level by raising levels of igA, an antibody found in your mucus that kills cold germs. In most cases, igA is a good indicator of immune system health—the more igA you have, the stronger your immune system is.

When a research team tested a group of college students in 1999, they found that people who had sex at least twice a week had higher levels of igA in their system. They came to the conclusion that by regularly exposing themselves to all the various germs other people carry, these people were constantly building an immunity to a range of viruses and bacteria, similar to the way children who eat dirt wind up healthier.

On the other hand, the abstinent students who didn’t have that intimate contact had fewer biological defenses because their bodies weren’t getting those tiny bumps of exposure. On a final, freakish third hand, having sex too much (three or more times per week) drops those igA numbers right back down to abstinence levels.

4 Reduces Risk Of Prostate Cancer

Maybe going for the gold in the cosmic sexolympics won’t help your immune system, but it may very well reduce your risk of getting prostate cancer. Prostate cancer normally affects men older than 45, with most diagnoses cropping up around the age of 70. In a massive eight-year study that followed 30,000 men, the National Cancer Institute found that men who popped one off at least 21 times per month were one-third less likely to develop prostate cancer than men who averaged four or five monthly deposits. During the course of the study, 1,500 participants came down with prostate cancer, further clarifying the statistics.

Despite the clear results, the researchers weren’t sure why frequent ejaculations had an effect on prostate cancer. One of the main theories is that it keeps the passages open and prevents buildup. As the good folks at Johns Hopkins put it, all that release sort of “cleans house” up in the prostate, washing away fluids and tissue that could become infected or inflamed.

3 Sexual Genetics

Most people picture the Stone Age as a rampaging sex frenzy peppered with raucous interbreeding between Neanderthals and Homo Everythings, the kind from which you wake up three million years later with a pounding headache and an acute sense of regret. While it’s true that Homo sapiens and Neanderthals had some liaisons between the sheets, it didn’t happen nearly as often as we once thought. Spicy or not, the study of ancient sex is giving us something else: clues to the movements of early humanity.

The genetic similarities between Neanderthals, Denisovans, and a recently discovered African ancestor are giving us a better idea of the migration of early humans. The most prevalent theory has long been the “Out of Africa” theory, which states that all modern humans started in Africa, moved east, then migrated north into the Eurasia region.

But based on the Neanderthal genome that was published in 2010 (along with gene testing from people living in various regions in Africa, Asia, and Europe), it’s beginning to look more complicated than that. Early humans may have migrated out of Africa, mixed with Neanderthals, then gone back to Africa carrying a trace of Neanderthal genetics, which then spread and replaced the native genes. To this day, about 4 percent of our genes were inherited from our Neanderthal ancestors.

2 High-Pitched Voices

If you were asked to form a mental image of masculinity, what would you picture? Muscles? Beards? Deep Mufasa-esque voices echoing through the canyons of your own insecurity? According to research, most women feel the same way about what constitutes manliness, and those are the type of men most women look for in a mate. A deep voice is inextricably linked to higher testosterone levels, which is further associated with genetic strength—big men make better baby daddies.

However, this may be one of the few cases of a woman’s body telling her the wrong thing. As it turns out, men with higher-pitched voices pack a more potent punch. A paper published in 2011 found that although deeper-voiced men were considered more attractive, they invariably had lower concentrations of sperm than their less-attractive falsetto counterparts. The reason could be a simple evolutionary trade-off—masculine men have more chances to reproduce, so each try doesn’t necessarily need to be a winner. Men who don’t get that many chances need to throw everything they’ve got into it, because who knows when they’ll get another shot?

1 Human Penile Spines

Penile spines, as you may know, are spines on the penis. Plenty of animals have them, from the humble field mouse to the proud buffy-tufted marmoset. They’re usually used to rake the inner walls of a female’s vagina after sex to induce ovulation or to prevent the female from mating with anyone else. As it turns out, humans have the genetic coding to create penile spines, too—at some point, we had prickly pickles just like everyone else in nature.

So what happened to them? A team of biologists at the Stanford School of Medicine set out to compare the DNA differences between humans and chimpanzees, one of our closest living relatives, and found a very small but very important deviation. While we still have the genes for penile spines, we lost the switch that activates those genes.

You see, DNA is made up of different types of genomes. Protein-coding genes are like factories—they make proteins that are assigned to different roles. Non-coding DNA strands are like light switches—they’re responsible for turning a protein-coding gene on or off at a specific time. In humans, the penile spine protein factory is still there, waiting to be flipped on, but the switch disappeared.

Why? The best guess is that mammals that mate with a lot of partners tend to have more prominent spines, while mammals that practice pair bonding have recessed spines—for example, chimp spines are more like bumps. At some point, it became more advantageous for humans to pair together for longer, and the spine switch was lost along the way. Love is a beautiful thing.