The evolutionary trait leading to the female orgasm began as a way to stimulate ovulation in early mammals, scientists from Yale University and the Cincinnati Children’s Hospital reported in new research published online Monday.
Writing in the Journal of Experimental Zoology Part B Molecular and Developmental Evolution, Gunter Wagner, a professor of ecology and evolutionary biology at Yale as well as a member of the university’s Systems Biology Institute, and his colleagues set out to investigate what role the female organism played in biology, as it appeared to be unrelated to human reproduction.
“Prior studies have tended to focus on evidence from human biology and the modification of a trait rather than its evolutionary origin,” Wagner said in a statement. Instead, his team focused on a particular physiological trait known to accompany human female orgasms: the neuro-endocrine discharge of prolactin and oxytocin. They found that in many other mammal species, this release is associated with ovulation, suggesting that there is some link between the two.
In short, they concluded that the female organism may have originally been an adaptation which was directly involved in reproduction by inducing ovulation. Over time, however, the importance of its function was diminished, resulting in it becoming relegated to a secondary role in people.
Development of cyclical ovulation linked to relocation of the clitoris
The research could help solve a mystery that has dated back to the era of the Greek philosophers, as past research in the area had found no known link between female orgasms and the number of offspring or the reproductive success rate of humans, the authors explained in a statement.
Biologically speaking, reproduction is extremely diverse among different types of mammals, the researchers said. However, there are same characteristics that can be traced through the history of mammalian sexual activity. For example, the ovarian cycles of human females are not influenced directly by males, but the cycle is dependent upon males in some other mammalian species.
Wagner and his colleagues concluded that shows male-induced ovulation evolved first and that spontaneous or cyclical ovulation evolved later. Furthermore, by comparing female genitalia of different types of mammals, they found that the development of cyclical ovulation was linked to the relocation of the clitoris from within the copulatory canal, reducing the chances that it would receive enough stimulation during sex to produce the neuro-endocrine reflex known as orgasm.
“Homologous traits in different species are often difficult to identify, as they can change substantially in the course of evolution,” said co-author Mihaela Pavličev from the Center for Prevention of Preterm Birth at Cincinnati Children’s Hospital. “We think the hormonal surge characterizes a trait that we know as female orgasm in humans. This insight enabled us to trace the evolution of the trait across species.”
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