While the male orgasm’s role in facilitating reproduction has long been clear, the role of the female orgasm has remained more of a mystery. But emerging evidence from a recent Yale study suggests that the female orgasm may have helped induce ovulation in our evolutionary ancestors, thus functioning as an aid to conception.

The study, conducted by scientists at Yale and the Cincinnati Children’s Hospital, began as an inquiry into the ovulatory cycles of various mammals. Study co-authors Mihaela Pavličev from the University of Cincinnati College of Medicine and Günter Wagner from Yale’s Department of Ecology and Evolutionary Biology discovered that many female mammals release oxytocin and prolactin during sex — the same hormones released by women during orgasms. In certain mammals, such as rabbits and cats, the release of these hormones triggers the release of eggs from the female’s ovaries. The study by Gunter and Pavlicev was published in the Journal of Evolutionary Zoology: Part B, Molecular and Developmental Evolution on Aug. 1.

“In mammals such as rabbits and cats, copulation is necessary in order for ovulation to occur,” Wagner said.  He added that the study implicates that the origins of the female orgasm can be in part understood by looking at the evolutionary benefits of the female orgasm in other mammalian relatives.

Although numerous mammals, including human women, experience spontaneous ovulation on a monthly basis, Wagner and Pavličev found that male-induced ovulation predated spontaneous evolution. Spontaneous evolution, according to the study authors, arose with the formation of social groups that gave females access to regular sex with males. Prior to this, male-induced ovulation allowed females to take full advantage of rare encounters with biologically compatible males. Based on this, the study authors argued that the human female orgasm could have its roots in a mechanism for the release of eggs during sex. According to the researchers, as women developed the ability to release eggs in a regular cycle, the ancestral ovulatory system became redundant and the female orgasm was relegated to a secondary position.

The study is one of the first of its kind to explore the evolutionary origins of the female orgasm. Elisabeth Lloyd, philosopher at Indiana University and author of the book “The Case of the Female Orgasm,” said the study presented a “very interesting hypothesis” but also found some problems with the hypothesis in terms of the evidence. Lloyd also took issue with the fact that the study focused explicitly on the hormonal aspect of the female orgasm, when she considers orgasms to be a “muscular spasm and neurological reflex.”

“The accompanying hormonal surges that go along with it are also very significant, but they are not defining of orgasm,” Lloyd said.

David Puts, an evolutionary anthropologist at Pennsylvania State University, echoed Lloyd’s argument, stating that the research addressed one particular aspect of orgasms. He added that it would be more accurate to describe the paper as exploring the origins of one important component of orgasm, rather than the phenomenon as a whole. However, Puts also voiced his support for the paper, stating that he was “relatively convinced” that the hormonal changes studied by the researchers, albeit later co-opted, were ancestrally a part of induced ovulation.

According to Puts, in exploring the ancestral state of the orgasm, the study provided important new evidence about why the orgasm evolved for its present function. However, Puts added that plenty more work needs to be done to build on existing evidence. Puts pointed out, for instance, that researchers have previously treated women with oxytocin, the hormone released during orgasm, and found that their reproductive tracts moved sperm towards the egg. However, Puts added that such research need to be replicated and further developed before it can provide conclusive results.

The female orgasm has long eluded many, and, according to Puts, relatively sparse evidence together with the subject’s inherent sensitivity come together to make the possible evolutionary functionality of the female orgasm one of the most contentious topics in the study of human sexuality.