Thanks to some enterprising scientists out there, we now know a lot of interesting things about the mechanics and evolution of sex. Here are five interesting theories and factoids about why human sexuality developed the way it did.
1. The penis may have evolved to scoop out rival sperm.
If you’ve ever had the opportunity to examine the human penis, you’re probably familiar with its unique shape. Most of us simply accept the “mushroom tip” as a fact of life; a little weird looking but nothing worth talking about. Then again, most of us aren’t evolutionary psychologists.
Gordon Gallup’s “semen displacement theory” suggests the distinctive mushroom-capped glans, and the coronal ridge that forms underneath it, are actually designed to remove rival semen from the vagina.
Back in 2003, Gallup and a team of researchers from the State University of New York-Albany conducted a study using different dildos, artificial vaginas, and yes, a homemade semen recipe to help demonstrate the theory. They found that dildos featuring a coronal ridge (like that of a real penis) displaced 91 percent of semen present in the vaginal canal. Dildos without the ridge only displaced 35 percent.
2. Deep voices don’t equal high sperm quality.
Tall, dark and handsome are three qualities some women look for in an “ideal" man. One feature that tends to accompany those traits is a deep, commanding voice. But as it turns out, that might not be as desirable as it sounds (pun intended).
Evolutionary biologist Leigh Simmons of the University of Western Australia located 54 heterosexual men and 30 heterosexual women to participate in a study. Simmons and her team recorded the voices of the male participants. She later played the recordings for the female volunteers, and asked them to rate the voices in regards to masculinity and attractiveness. The women, unsurprisingly, gravitated toward the deeper voices.
The male volunteers were then ask to collect a semen sample and return it to Simmons for lab analysis. Using a computer-assisted sperm-analysis system, Simmons found that men with “more attractive” voices didn’t have better sperm quality than those with “less desirable” voices. The sperm collected from the deep-voiced men were “perfectly motile” and fertile, "but had fewer sperm cells in the ejaculate," National Geographic reports. The reason? Testosterone can lower voice pitch. But too much of it can interfere with sperm production.
3. Ever get depressed after sex? There’s a name for that.
If you’ve never experienced the post-sex blues, consider yourself lucky. For those who have, you’re not alone. It’s called “postcoital dysphoria” and it’s more common than it sounds.
A 2011 Australian study published in the International Journal of Sexual Health found that one-third of women said they’ve felt depressed, “even after satisfactory sex.” The researchers went on to claim that the condition affects around 10 percent of women regularly.
Debby Herbenick, associate director of the Center for Sexual Health Promotion at Indiana University in Bloomington, Ind. told Everyday Health, “There’s no doubt that many men and women swear that they have these negative feelings after sex, and occasionally after masturbation.” Dr. Michael Krychman described the feeling as “buyer’s remorse.”
Symptoms of postcoital dysphoria include melancholy, tearfulness, anxiety, irritability or feelings of restlessness immediately after intercourse.
4. Being horny makes things seem less gross.
Sex, fun as it is, can be a little gross at times. Bodily fluids in general are a little gross. So it makes sense that our brains would find a way to help us get over it, and get to it. Anything for the sake of procreation, right?
As LiveScience reported, a team of researchers set out to test if sexual arousal can minimize our natural disgust response. To test the theory, they asked 90 heterosexual female volunteers to complete 16 different “revolting” tasks, like drinking juice f a cup with a large plastic insect in it, wiping their hands with a used tissue and sticking their fingers in a bowl of used condoms (relax; the insect was plastic, the tissue was colored with ink and the condoms were new and only covered in lubricant).
The scientists divided the volunteers up into three groups. One was shown female-friendly erotica. Another was shown adrenaline-inducing films about sports, like rafting or skydiving. The last third, the control group, were shown footage of a train ride.
The researchers found that the women exposed to sexually arousing material found the “tasks” far less gross than the other participants. Researcher Charmaine Borg, a psychologist at the University of Groningen in the Netherlands, told LiveScience, “From a clinical angle, these findings give us insight into important problems or sexual arousal and sexual pain disorders… Perhaps women with sexual dysfunctions such as dyspareunia or vaginismus, arousal does not impact on disgust.”
5. We used to have penis spines.
Anyone who has watched videos of lions having sex will agree that penile spines seem like absolute bummers. The spines, as defined by National Geographic, are usually small barbs of keratin (a type of hard tissue) that line the outside of the organ. They make sex painful for the female, but aid in the process of fertilization. Luckily, the human penis has evolved to be smoother and simpler, which likely makes sex much more enjoyable. But that’s a luxury we modern humans have been afforded. Our ancestors may not have been so lucky.
Developmental biologist Gill Bejerano says that six million years back, the common ancestor of chimpanzees and humans was endowed with penile spines. But as National Geographic reports, the "'penile spine enhancer' code disappeared from human genes before our common ancestor split into modern humans and Neanderthals, around 700,000 years ago."
Study co-author David Kingsley suggests that our move toward monogamy may have impacted the genetic shift. Penile spines help eliminate rival sperm. This comes in handy when sperm competition is high. And as Kingsley told National Geographic, males “are not just present during the competitive act of fertilization—they establish long-term relationships with females.”