03 Oct How Did the Female Orgasm Evolve?
MedicalResearch.com Interview with:
Günter P. Wagner PhD
Department of Obstetrics, Gynecology and Reproductive Sciences
Yale Medical School
Department of Ecology and Evolutionary Biology
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: It has been known for a long time is that female orgasm is not necessary for pregnancy or any other aspect of human reproduction, and so people have asked themselves for a long time, why is there female orgasm, when there is not obvious biological role for it? It is important to note that there is also no evidence for indirect effects on fertility, meaning that more “orgasmic” women, on average, do NOT have more kids as less orgasmic woman. So how could this have evolved, given that orgasm is a fairly complex physiological process that is unlikely to originated just by accident.
- Our study aimed at testing the idea that female orgasm is a holdover from a time in evolution, where ovulation required genital stimulation to happen. For instance rabbits do not ovulate unless the female rabbit copulates with a male rabbit. In contrast women and other primates ovulate once a month regardless of whether there is a male around or not. In fact, in a previous study we showed that so-called Copulation Induced Ovulation (CIO) is evolutionarily older than spontaneous ovulation, which means that “we” evolved from an ancestor that had CIO.
- In order to further test this model, which we call the “Ovulatory Homologue Model,” we, that is Professor Pavličev and I, thought to see whether a pharmaceutical agent that inhibits orgasm in women also inhibits ovulation in an animal that needs copulation to ovulate. We used the chemical called Fluoxetine, which in humans causes difficulty reaching orgasm.
- We treated female rabbits with Fluoxetine for two weeks and then measured the number of eggs produced after copulation and compared that number to a control group without Fluoxetine. We found that in fact Fluoxetine decreases the number of eggs released after copulation.
- We take this result to support the idea that the brain regions that are engaged in female orgasm are the same as those that mediate CIO. This also supports the idea that one (FO) evolved from the other (CIO).
MedicalResearch.com: What should readers take away from your report?
Response: The main conclusion is that female orgasm is a physiological process that originated for a reproductive role, namely to trigger the release of egg cells from the ovary, but has lost this function in the primate [including human] lineage. This probably happened about 50 million years ago.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: The main question for future research is that we do not need anymore to explain why female orgasm has originated, but why it is still there. If it has no biological function at all, then one would expect that it should have degenerated and has been lost. May be female orgasm plays another role that we have overlooked so far? Is there a biological function that is NOT relate to reproduction? Or are there some constraints that make it difficult to lose this biological trait, maybe because of some side effects of mutations that affect FO?
MedicalResearch.com: Is there anything else you would like to add?
Response: Understanding the natural history of female sexuality has many implications for how people think about female sexuality, and their attitudes towards female sexuality. The, still incomplete, picture emerging from the research that Professor Pavličev and I are doing is one where female sexuality does not seem to be limited to its role in reproduction, but is much more complex and multidimensional.
An experimental test of the ovulatory homolog model of female orgasm
Mihaela Pavlicev, Andreja Moset Zupan, Amanda Barry, Savannah Walters, Kristin M. Milano, Harvey J. Kliman, and Günter P. Wagner
PNAS first published September 30, 2019 https://doi.org/10.1073/pnas.1910295116
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