A woman’s body is like a violin and all and that it takes a terrific musician to play it right.
-JD Salinger

Human female orgasm is a mystery. To all of us earthlings, we do not know what reliably triggers the female orgasm. To the scientific community, including Aristotle (Leroi, 2014), the female orgasm is a conundrum because the orgasm in women is not needed for reproductive purposes. Plus, the female orgasm does not usually accompany during the penile- vaginal intercourse; the orgasm is more common during female masturbation or homosexual “entanglement” than heterosexual intercourse (Garcia et al., 2014).

On the other hand, male orgasm is not a mystery. Male orgasm is always required for ejaculation and sperm transfer. What is the function of female orgasm? Why do females have it?

There are various, but 2 leaning evolutionary explanations for why do females have the orgasm. The first explanation argues that the female orgasm still plays an adaptive role in reproduction. The second explanation argues that the female orgasm is a by-product, the shared developmental feature as the basis of clitoris and penis (Symons, 1979). In men, orgasm is a necessity; therefore, the female orgasm is the upshot of male orgasm.

I will describe further evolutionary explanations and evidences associated with them. Before I do that, let me quickly summarize recent scientific reports on the female orgasm. The paper that recently came out last month by Pavlićev and Wagner (2016) shed lights on the origin of female orgasm (i.e. what is the beginning of female orgasm in our evolutionary history?).

Most evolutionary explanations I will soon be discussing obtained their evidence from contemporary men and women.  Pavlićev and Wagner (2016) argued that doing this does not necessarily point out the evolutionary origin. They traced the origin of the female orgasm by doing comparative analysis. Their main conclusion is that the contemporary female orgasm is the result of the ancient induced ovulation system.

Contemporary human females have ovulatory cycle regulation that is spontaneous i.e. autonomous hormone cyclicity, followed by ovulation and pregnancy, if fertilized. There are other types of ovulatory cycle regulations: ovulation induced by environments, ovulation induced by the presence of males and ovulation induced by copulation. Although they are not clearly distinct from each other, phylogenetic evidence from comparative analysis shows that these other forms of ovulation are more ancestral and predates spontaneous ovulation in human females.

Secondly hormonal surge, such as PRL that accompanies during female orgasm, but not during copulation. Further detailed similarities between hormonal changes during female orgasm and hormonal signals that cause ovulation, particularly in copulation-induced ovulation, led the authors to conclude that the female orgasm is a homologue to the physical changes that cause ovulation in other species, possibly going back to the most recent common ancestors of therian mammals, which are the ancestors of marsupials and placental mammals.

Thirdly, the authors showed that in later arising species like us and other primates, clitoris (often key to female orgasm) is located away from the vagina. In other types of ovulatory regulation, the stimulation of clitoris attached or closer to vagina during copulation leads to the ovulation and consequently fertilization. The modern female clitoris, now free from copulation-induced ovulation, possibly has evolved as the new orgasmic functions that could serve as secondary adaptations.

Female orgasm affects sperm intake and retention

One hypothesis is that female orgasm increases the chances of successful reproduction. Evidences have shown that female orgasm facilitates the sperm uptake and transport the sperms up to the cervix, closer to the egg. The orgasm also decreases the sperm loss from flow back by facilitating the interaction between sperm and oviductal epithelium (When woman stands up or move after intercourse, the sperms could flow back away from the egg). Baker and Bellis (1993) found that female orgasm within 1 minute before and 45 mintues after male ejaculation was associated with higher sperm retention in the reproductive tract, compared to no orgasm or orgasm at different times.

Female orgasm activates sperm ejaculation and increases the future make-out sessions

Prolactin secretion during orgasm may make sperm more capable of fertilizing an egg (Puts and Dawood, 2006), and contractions during orgasms may excite male ejaculation (Meston et al., 2004). Also, the increased pleasurable sensations may induce females to have sex again with males with whom they achieved orgasms (Puts and Dawood, 2006).

Good-genes hypothesis

The idea is that if the female orgasm affects sperm retention and/or facilitates sperm intake, therefore affecting fertilization, female deferentially would have orgasm with males who have good genes. Bodily symmetry is a marker of genetic quality and Thornhill et al. (1995) predicted that higher orgasm rates in females would occur from having sex with more symmetrical males. The evidence is that male partner’s bilateral symmetry is positively correlated with female orgasm rate from intercourse, but not from oral sex or masturbation. Women are also more likely to have orgasm with men who are considered more physically attractive (Shackelford et al., 2000).

Pair-bonding hypothesis

Oxytocin, so called pair-bonding hormones, rise during sex and particularly during orgasm (Carmichael et al., 1987). Pair-bonding consequences have effects on relationship outcomes, paternity and paternal investment.

Conclusion

There are lots of great articles I failed to cite here. Plus, there are counterarguments and limitations within articles cited here. But, my goal here is just to summarize and inform you some evolutionary arguments proposed and evidenced.

Some original by-product explanations posit that female orgasm is the by-product of male orgasm, which is necessary for sperm transfer and ejaculation. On the other hand, recent evidence by (Pavlicˇev & Wagner, 2016) suggests that female orgasm is the by-product of ancient adaptation, namely for ovulation during the presence of males or copulation.

My opinion is that female orgasm is the by-product and is currently serving secondary adaptive roles in reproduction. But my views possibly could change. Next, I am going to order and read The Case of the Female Orgasm: Bias in the Science of Evolution by Elisabeth Lloyd (2005) who questioned and argued that female orgasm, serving secondary adaptive roles in contemporary society, is a very false notion.

References

Baker, R. R. & Bellis, M. A. (1993). Human sperm competition: Ejaculate manipulation by females and a function for the female orgasm. Animal Behaviour, 46, 887-909.

Carmichael, M. S., Humbert, R., Dixen, J., Palmisano, G., Greenleaf, W., & Davidson, J. M. (1987). Plasma oxytocin increases in the human sexual response. Journal of Clinical Endocrinology and Metabolism, 64(1), 27-31.

Garcia, J. R, Lloyd, E. A., Wallen, K., & Fisher, H. E. (2014). Variation in orgasm occurrence by sexual orientation in a sample of U.S. singles. The Journal of Sexual Medicine. 11, 2645–2652.

Leroi, A. M. (2014). The lagoon: How Aristotle invented science. New York: Viking.

Lloyd, E. A. (2005a). The case of female orgasm: Bias in the science of evolution. Cambridge, Massachussettes: Harvard University Press.

Meston, C. M., Levin, R. J., Sipski, M. L., Hull, E. M., & Heiman, J. R. (2004). Women’s orgasm. Annual Review of Sex Research, 15, 173–257.

Pavlićev, M., & Wagner, W. (2016). The Evolutionary Origin of Female Orgasm. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution.

Puts, D. A., & Dawood, K. (2006). The Evolution of Female Orgasm: Adaptation or Byproduct?. Twin Research and Human Genetics, 9(3), 467-472. doi:10.1375/twin.9.3.467

Shackelford, T. K., Weekes-Shackelford, V. A., LeBlanc, G. J., Bleske, A. L., Euler, H. A., & Hoier, S. (2000). Female coital orgasm and male attractiveness. Human Nature, 11(3), 299-306.

Symons, D. (1979). The evolution of human sexuality. New York, NY: Oxford University Press.

Thornhill, R., Gangestad, S. W., & Comer, R. (1995). Human female orgasm and mate fluctuating asymmetry. Animal Behaviour, 50, 1601-1615.

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