title: The Evolutionary Origin of Female Orgasm.
abstract: The evolutionary explanation of female orgasm has been difficult to come by. The orgasm in women does not obviously contribute to the reproductive success, and surprisingly unreliably accompanies heterosexual intercourse. Two types of explanations have been proposed: one insisting on extant adaptive roles in reproduction, another explaining female orgasm as a byproduct of selection on male orgasm, which is crucial for sperm transfer. We emphasize that these explanations tend to focus on evidence from human biology and thus address the modification of a trait rather than its evolutionary origin. To trace the trait through evolution requires identifying its homologue in other species, which may have limited similarity with the human trait. Human female orgasm is associated with an endocrine surge similar to the copulatory surges in species with induced ovulation. We suggest that the homolog of human orgasm is the reflex that, ancestrally, induced ovulation. This reflex became superfluous with the evolution of spontaneous ovulation, potentially freeing female orgasm for other roles. This is supported by phylogenetic evidence showing that induced ovulation is ancestral, while spontaneous ovulation is derived within eutherians. In addition, the comparative anatomy of female reproductive tract shows that evolution of spontaneous ovulation is correlated with increasing distance of clitoris from the copulatory canal. In summary, we suggest that the female orgasm-like trait may have been adaptive, however for a different role, namely for inducing ovulation. With the evolution of spontaneous ovulation, orgasm was freed to gain secondary roles, which may explain its maintenance, but not its origin.
authors.affiliation: Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio. mihaela.pavlicev@cchmc.org.|Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio. mihaela.pavlicev@cchmc.org.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Pavličev
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut.|Yale Systems Biology Institute, Yale University, West Haven, Connecticut.|Department of Obstetrics, Gynecology and Reproductive Sciences, Yale Medical School, New Haven, Connecticut.|Department of Obstetrics and Gynecology, Wayne State University, Detroit, Michigan.
authors.forename: Günter
authors.initials: G
authors.lastname: Wagner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002987:Clitoris / Q000502:physiology; D003075:Coitus / Q000502:physiology; D003307:Copulation / Q000502:physiology; D005260:Female; D005836:Genitalia, Female / Q000033:anatomy & histology; D006801:Humans; D008297:Male; D008322:Mammals; D009948:Orgasm / Q000502:physiology*; D010060:Ovulation / Q000502:physiology*; D010802:Phylogeny