Experts aren't entirely sure why humans evolved orgasms

Orgasms may be a uniquely human trait. Sex researchers debate why we evolved this fantastic ability

By Troy Farah

Science & Health Editor

Published February 14, 2023 6:55PM (EST)

Couple in bed holding hands passionately (Getty Images/Sadeugra)
Couple in bed holding hands passionately (Getty Images/Sadeugra)

"Did you get there?" may be one of the most commonly asked questions in the bedroom. When an individual climaxes, they experience one of the truly blissful elements of being human. Why, then, is defining an orgasm not an easy task?

Modified, the old adage often applied to censoring pornography would go, "I know it when I feel it." This speaks to the fact that only an individual can ever really know what an orgasm means to them. It's a highly subjective experience.

Sex researchers are still figuring out what an orgasm is exactly. While the answer is more complex than it may seem, one of the fundamental questions about the orgasm is why humans evolved this trait in the first place, especially in women. Moreover, it's not clear that other animals experience orgasms. Humans may be special in that regard.

It may seem obvious why humans gained this ability. An orgasm feels good, so a little reward during or after sexual reproduction would presumably encourage mating, increasing the chances of passing down one's genes. This is the basis of evolution in a nutshell: advantageous traits that help us survive and keep our DNA-based game of telephone going are more likely to stick around in our genome.

But orgasm phenomena — not to mention evolution — are a lot more complex than an oversimplified model of gene flow. Orgasms may have evolved as a means of encouraging mating, but this alone isn't enough to guarantee their persistence in our genetic histories. However, they have clearly impacted us in a profound way, considering the orgasm's elevated place in our culture and our health. Where, then, did this feature even come from?

Experts aren't entirely sure, but attempts to understand begin by defining the orgasm, which can be thought of as the penultimate intersection between the body and the mind. On one level, the orgasm is like a reflex not unlike a sneeze: a complex, automatic response to certain stimuli, especially (or exclusively) something sexually arousing.

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A good orgasm can be an intensely pleasurable experience followed by a release of sexual tension. It can involve a suite of involuntary pelvic contractions in the bony structure near the base of the spine, while also flushing the body with hormones and neurotransmitters like serotonin and dopamine, which help cells send signals to one another.

Orgasms are really good for human beings. Their role in pain and stress relief, promoting sleep and social bonding is beneficial to human health. Yet, despite these basic facts, researchers continue to debate what, precisely, an orgasm is. Humans seem to be unique in the animal kingdom when it comes to this capacity for bliss.

Clearly, many male animals ejaculate — that is, if the creature has a penis, it can spew its sperm in a way that launches it great distances, increasing the chances of successful reproduction. The term "ejaculate" comes from the Latin verb "ejaculari," which means "dart out," combined with "jaculari," which is related to the word "javelin," or "to throw." 

(Just a quick note on sex and gender: Animals don't have gender, so referring to them as male or female refers to sex and simply means what kind of genitalia and chromosomes it has.)

Just because an animal ejaculates does not mean it orgasms.

Some animals do more shooting than others. A species of spiny anteater called short-beaked echidnas (Tachyglossus acelatus) has a penis with two heads that resembles a bivalve showerhead. Ejaculation alternates between each one, giving the echidna maximum "sperm motility," which is the ability for its swimmers to move through the female reproductive tract.

But just because an animal ejaculates does not mean it orgasms. Both are related but distinct physiological processes, and as many people already know from experience, there's a big difference. For example, one 2009 study in the International Journal of Impotence Research gave a handful of healthy male volunteers a drug called silodosin, which made it so they couldn't ejaculate but still orgasm. Plenty of people also orgasm or ejaculate without one being connected to the other.

It's much harder to study subjective experiences in animals. While some experts theorize that certain animals like rabbits may orgasm, it hasn't been definitively proven. And yet, we don't know how to reliably set them off in humans either.

"I always joke, if I knew how [an orgasm] was triggered, I wouldn't be here. I'd just be rich somewhere with my device I sold to trigger that anytime you felt like it," Dr. Nicole Prause, a neuroscientist and sexual psychophysiologist who founded Liberos, a sexual biotech company in Los Angeles, told Salon. "We still don't know how orgasms are triggered. We can trigger them with some reliability with spinal cord stimulation. But these are implants — this isn't something you can do from the outside reliably."

"I always joke, if I knew how [an orgasm] was triggered, I wouldn't be here. I'd just be rich somewhere with my device I sold to trigger that anytime you felt like it."

Given rampant sexism in science and medicine, it isn't surprising that the male orgasm is better studied than the female orgasm. The question of why it evolved in women is especially perplexing to some researchers. It was originally thought the contractions that occur during orgasms could help siphon semen into the uterus. This is known as uterine upsuck theory.

"The uterine upsuck theory was the idea that when women had an orgasm, the cervix would dip into the seminal pool that was in the vagina, and therefore, suck the semen up. That would catapult it towards the egg," Prause said. "And people actually tested this — they put tracers in the pool in the vagina and found it does not upsuck."

Now, a common theory is that orgasms in women or people with vaginas are just a byproduct of our evolution like wisdom teeth. It's a vestigial leftover, something not useful for reproduction or survival, such as wings on flightless birds.

"The byproduct theory is women were never meant to have climaxes," Prause said. "It's just that our clitori are similar enough to the penis that we can manage it sometimes, depending on what the particular anatomy or physiology is of different women."

In the end, these are all only theories. More evidence is needed to answer the many outstanding questions surrounding orgasms. Because of Western culture's puritanical roots and a lack of robust sex education, orgasms are often depicted as gross or shameful.

Regardless of one's strong opinions about these euphoric incidents, they're a normal part of human health. For better or worse, most people wouldn't be here without an orgasm, and we could stand to give them a little more credit.

Orgasms aren't simply something that feels good to make us reproduce. They relate to so much more about human health and identity.

By Troy Farah

Troy Farah is a science and public health journalist whose reporting has appeared in Scientific American, STAT News, Undark, VICE, and others. He co-hosts the drug policy and science podcast Narcotica. His website is and can be found on Twitter at @filth_filler

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Biology Deep Dive Ejaculation Human Sexuality Orgasm Science Sex