Do animals have orgasms?

Be it a salmon swimming upstream or a turtle mounting a shoe, creatures obey the impulse that commands them to reproduce. But do they, at the end of the great energy expenditure, feel anything akin to what humans call an orgasm?

There's no clear list of animals that can orgasm. For one, research on physiological and neurological activity in animals during sexual behavior looks mostly at primates and rodents, David Puts, a professor of anthropology and psychology at Penn State, told Live Science in an email. And because animals can't describe their own experiences, we can't know for sure if they feel what humans feel during climax.

We can, however, compare observed physical and neurological behaviors. "Many female primates exhibit behaviors that are similar to those exhibited during orgasm in women," Puts said. These behaviors include a clutching reaction; changes in bodily tension and facial expressions; changes in respiratory patterns; vocalizations; and contractions of the vagina, anus, pelvic muscles and uterus, he said.

"We can also look at behavior and brain activation patterns, which appear similar across male mammals," Puts said.

The definition of an orgasm has evolved over time to reflect both the physiological process as well as the characteristic experience of intense pleasure. A 2016 paper published in the journal Socioaffective Neuroscience & Psychology defines the physiological process as "a spinal reflex that results in rhythmic muscle contractions of the pelvic floor and anus." In males, this response also typically entails a urethrogenital reflex that coincides with semen emission and ejaculation, while females have contractions of the uterus and cervix.

Related: What were the first animals to have sex?

But even with these observations, it's difficult to conclude with certainty whether these animals are having what humans describe as an orgasm. "We can never know if they feel or interpret it the exact same way," James Pfaus, a professor of neuroscience at Charles University in Prague and director of research at the Czech National Institute of Mental Health's Center for Sexual Health and Intervention, told Live Science in an email. Pfaus is also the first author of the 2016 paper.

However, the term "orgasm-like response" cuts through the uncertainty of how other animals experience what appears to be a sexual climax, Pfaus said. Ultimately, even if we can't assert that other animals have orgasms, they have something that closely resembles an orgasm.

"My feeling is that all mammals probably have [orgasm-like responses]," he said. Our understanding of anatomy across species informs his belief. While clitorises and penises vary in structure across mammals, the distribution of nerves throughout those anatomical features "is virtually the same" in all mammals and across sex. As mammals have evolved, the hormonal and neurochemical mechanisms involved in sex have been largely conserved, Pfaus explained.

That's not to say nonmammals don't feel pleasure or have an orgasm-like response during sex. Rather, because research on orgasms has favored mammals, it leaves the opportunity for other scientists to investigate physiological and neurological responses during sex in reptiles, amphibians, birds and other nonmammals.

Why do orgasms exist in the first place? "The 'why' would take us many days to discuss," Pfaus said. Put simply, however, "Orgasms serve two masters: reproduction and reward," he said.

Thankfully, one doesn't need to understand the purpose of an orgasm to enjoy one.