9 Surprising Facts About the Scientific Study of Sex

vadimguzhva/iStock via Getty Images
vadimguzhva/iStock via Getty Images

The scientific study of sex is much more exciting than an awkward sex ed class. While writing my book Sex Weird-o-Pedia, these were some of the most interesting facts about science and sex that I came across.

1. Some sex researchers didn't want their findings to get into the wrong hands.

The pioneering sex researcher Richard von Krafft-Ebing didn’t want his knowledge in the hands of ordinary folk. So he wrote Psychopathia Sexualis, the founding document of modern sexology—which was published in Germany in 1886 then translated and published in English in 1939—in Latin to discourage regular Joes (and/or Janes) from reading it.

2. You burn more calories mowing the lawn than you do having sex.

Young woman poses for selfie while mowing the lawn
Alina Rosanova/iStock via Getty Images

Sex might seem strenuous when things get hot and heavy, but it's usually not that great of a workout. You'd have to go at it for nearly 200 minutes to burn as much energy having sex as you do during a 30-minute run. Even mowing the lawn burns about three times more calories than sex. According to the British Heart Foundation, sex burns about the same amount of energy per minute as ironing clothes.

3. A surprising number of mothers claim to be virgins.

In a 2013 study of several thousand pregnant women in the U.S. published by BMJ, about 1 percent of the participants claimed they were virgins when they gave birth. This, of course, calls into question the veracity of studies that rely on self-reported sexual behaviors.

4. Penicillin may have ignited the sexual revolution.

One economist says that penicillin, and not the birth control pill, was the real enabler of the sexual revolution. A study published in the Archives of Sexual Behavior in 2013 shows that penicillin contributed to a 75 percent decline in the number of deaths caused by syphilis from 1947 to 1957. Since the new treatment made sex safer, people started having riskier sex, which resulted in increases in the numbers of children born out of wedlock and teenage pregnancies.

5. Twins can have different dads.

A photo of fraternal twins
Aleksandr Zhurilo/iStock via Getty Images

While it is very rare, it is possible for fraternal twins to have two different fathers. What’s more common is for a rom-com to be based on this scenario.

6. Gender may influence how people handle sexual jealousy.

Research from evolutionary psychologists indicates that people’s gender influences how they react to sexual jealousy. For men, they react more strongly to sexual unfaithfulness than emotional infidelity. For women, it is the reverse. The theory behind these behaviors comes back to evolution: Males who were intolerant toward their wives becoming sexually active with other men were less likely to become an object of derision and more likely to see their own genes pass onto future generations. Women who prevented their husbands from emotionally bonding with other women reduced the chances of the men spending their resources on other women.

7. One of Ivan Pavlov's colleagues created his own (slightly x-rated) conditioning experiment with dogs.

You’re probably aware of Russian researcher Ivan Pavlov and his famous conditioning experiment in which he trained a dog to salivate at the sound of a bell. What you might not know is that one of Pavlov’s American students, W. Horsley Gantt, conditioned dogs to become sexually aroused when they heard specific tones. The experiment, according to Mandy Merck's In Your Face: 9 Sexual Studies, was intended "to study conflicts of the drives between ... experimentally induced anxiety states and sexual excitement."

8. Couples whose first child is a girl are more likely to get divorced.

Parents pay attention to their phones instead of their daughter
grinvalds/iStock via Getty Images

Married couples whose first child is a girl are more likely to get divorced than those whose first child is a boy. Scientists are split as to why this is. One theory is that female embryos are better able to endure maternal stress than male embryos, so pregnant women in unhappy marriages are less likely to have a miscarriage if the child they are bearing is a girl. But once they have a daughter, these couples are more likely to split up since there were already fissures in their relationship prior to the child’s birth.

9. There's a link between pubic hair and STIs.

A downside of pubic grooming is that it might raise STI risk. In a study conducted by a University of Texas scholar, people who regularly shaved their pubic areas contracted STIs about 80 percent more often than those who never shaved down there. One suggestion is that those who regularly shave are more likely to tear their skin, making it easier for viruses to enter the body.

Ross Benes is the author of Sex Weird-o-Pedia: The Ultimate Book of Shocking, Scandalous, and Incredibly Bizarre Sex Facts.

Why Thousands of 'Penis Fish' Washed Up on a California Beach

Kate Montana, iNaturalist // CC BY-NC 4.0
Kate Montana, iNaturalist // CC BY-NC 4.0

Nature works in mysterious ways. The latest example materialized at Drakes Beach near San Francisco, California, in early December, when visitors strolling along the shore stumbled upon what looked to be the discarded inventory of an adult novelty shop. In fact, it was thousands of Urechis caupo, a marine worm that bears more than a passing resemblance to a human penis.

The engorged pink invertebrate, which is typically 10 inches in length, is native to the Pacific coast and frequently goes by the less salacious name of “fat innkeeper worm.” Burrowing in sand, the worm produces mucus from its front end to ensnare plankton and other snacks, then pumps water to create a vacuum where the food is directed into their tunnel. Since it builds up a small nest of discarded food, other creatures like crabs will stop by to feed, hence the “innkeeper” label.

You can see the worm in "action" here:

Because the worms enjoy a reclusive life in their burrows, it’s unusual to see thousands stranded on the beach. It’s likely that a strong storm broke up the intertidal sand, decimating their homes and leaving them exposed. The event is likely to thrill otters, as they enjoy dining on the worm. So do humans: Penis fish are served both raw and cooked in Korea and China.

[h/t Live Science]

The Horrors of Anglerfish Mating

Masaki Miya et al. "Evolutionary history of anglerfishes (Teleostei: Lophiiformes): a mitogenomic perspective," BMC Evolutionary Biology 10, article number: 58 (2010), Wikimedia Commons // CC BY 2.0
Masaki Miya et al. "Evolutionary history of anglerfishes (Teleostei: Lophiiformes): a mitogenomic perspective," BMC Evolutionary Biology 10, article number: 58 (2010), Wikimedia Commons // CC BY 2.0

When you think of an anglerfish, you probably think of something like the creature above: Big mouth. Gnarly teeth. Lure bobbing from its head. Endless nightmares. 

During the 19th century, when scientists began to discover, describe, and classify anglerfish from a particular branch of the anglerfish family tree—the suborder Ceratioidei—that’s what they thought of, too. The problem was that they were only seeing half the picture. The specimens that they were working with were all female, and they had no idea where the males were or what they looked like. Researchers sometimes found some other fish that seemed to be related based on their body structure, but they lacked the fearsome maw and lure typical of ceratioids and were much smaller—sometimes only as long as 6 or 7 millimeters—and got placed into separate taxonomic groups.

It wasn’t until the 1920s—almost a full century after the first ceratioid was entered into the scientific record—that things started to become a little clearer. In 1922, Icelandic biologist Bjarni Saemundsson discovered a female ceratioid with two of these smaller fish attached to her belly by their snouts. He assumed it was a mother and her babies, but was puzzled by the arrangement.

“I can form no idea of how, or when, the larvae, or young, become attached to the mother. I cannot believe that the male fastens the egg to the female,” he wrote. “This remains a puzzle for some future researchers to solve.”

When Saemundsson kicked the problem down the road, it was Charles Tate Regan, working at the British Museum of Natural History in 1924, who picked it up. Regan also found a smaller fish attached to a female ceratioid. When he dissected it, he realized it wasn’t a different species or the female angler’s child. It was her mate.

The “missing” males had been there all along, just unrecognized and misclassified, and Regan and other scientists, like Norwegian zoologist Albert Eide Parr, soon figured out why the male ceratioids looked so different. They don’t need lures or big mouths and teeth because they don’t hunt, and they don’t hunt because they have the females. The ceratioid male, Regan wrote, is “merely an appendage of the female, and entirely dependent on her for nutrition.” In other words, a parasite.

When ceratioid males go looking for love, they follow a species-specific pheromone to a female, who will often aid their search further by flashing her bioluminescent lure. Once the male finds a suitable mate, he bites into her belly and latches on until his body fuses with hers. Their skin joins together, and so do their blood vessels, which allows the male to take all the nutrients he needs from his host/mate’s blood. The two fish essentially become one.

With his body attached to hers like this, the male doesn't have to trouble himself with things like seeing or swimming or eating like a normal fish. The body parts he doesn’t need anymore—eyes, fins, and some internal organs—atrophy, degenerate, and wither away, until he’s little more than a lump of flesh hanging from the female, taking food from her and providing sperm whenever she’s ready to spawn.

Extreme size differences between the sexes and parasitic mating aren’t found in all anglerfish. Throughout the other suborders, there are males that are free-swimming their whole lives, that can hunt on their own and that only attach to the females temporarily to reproduce before moving along. For deep-sea ceratioids that might only rarely bump into each other in the abyss, though, the weird mating ritual is a necessary adaptation to keep mates close at hand and ensure that there will always be more little anglerfish. And for us, it’s something to both marvel and cringe at, a reminder that the natural world is often as strange as any fiction we can imagine.

Naturalist William Beebe put it nicely in 1938, writing, “But to be driven by impelling odor headlong upon a mate so gigantic, in such immense and forbidding darkness, and willfully eat a hole in her soft side, to feel the gradually increasing transfusion of her blood through one’s veins, to lose everything that marked one as other than a worm, to become a brainless, senseless thing that was a fish—this is sheer fiction, beyond all belief unless we have seen the proof of it.”

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