In The human penis as a semen displacement device, a 2003 paper published in Evolution and Human Behavior, a group of SUNY Albany psych researchers investigated the shape of the human penis to discover whether it could aid in "sperm competition," driving sperm out of the vagina prior to its own deposit -- something already observed in damselflies.
They devised an ingenious experiment.
They produced a cornstarch mixture that approximated human semen in the judgment of "three sexually experienced males," and deposited a single ejaculation's worth of the mixture in a transparent artificial vagina. Then they plunged a penis-shaped dildo -- with a flared glans -- into the vagina and observed that the action of the penis did, in fact, force the "competing" semen behind the glans, which then scooped it out of the vagina. A smooth dildo -- used as a control -- did not scoop the "semen" out of the artificial vagina.
The authors note that their on-campus surveys found that 12 percent of the students polled had had sex with multiple men in a 24 hour period and hypothesized that an evolutionary function of the glans is to force out the semen left by earlier partners prior to ejaculation.
The human penis as a semen displacement device
In the final phase of Experiment 2, we assessed the effect of the coronal ridge on semen
displacement. Using a knife, the coronal ridge was removed from phallus D taking care not to
destroy the glans. Fine sandpaper and an emory board were used to smooth the area that had
been cut away, and the resulting phallus (designated D
) is depicted in Fig. 5. Using the
low-viscosity flour and water semen mixture, five displacement trials were conducted with
both the intact and modified phallus.
As was true for cornstarch, the dilute semen lead to comparable displacement effects as a
function of phallus morphology. Phallus B displaced an average of 97.8%, phallus D 86.7%,
and phallus C 28.9% [(
<.0001]. The effects of semen viscosity and phallus
type were examined using a 3
2 factorial design. As shown in Fig. 6, there was a main
effect of Phallus Type [
<.0001], a main effect of Semen Viscosity
<.001], but no Phallus Type
Semen Viscosity interaction.
When Zoe Stavri woke up with a yeast infection, she had a strange and intriguing idea: what about adding some of her vaginal candida to sourdough starter?
Nick Sousanis, who delivered his doctoral dissertation in comic book form, has a new comic in the current Nature magazine, explaining the last 25 years’ worth of climate talks, as a primer in advance of the Paris climate talks next week.
Randall “XKCD” Munroe’s Thing Explainer: Complicated Stuff in Simple Words arrives in stores today: it combines technical diagrams and wordplay in pure display of everything that makes XKCD brilliant and wonderful in every way.
This minimalist multi-tool will see to it that instead of rocking a tool belt, you’ll carry just one. It’s shaped slightly like a key and weighs less than an ounce, so it plays nice with your keychain. The strong surgical-grade stainless steel blade will last, and is handy for everyday tasks like opening boxes and […]
The Code Black is our top-selling drone of all time—and for good reason. This powerful, palm-size drone is not only insanely fun to fly, but can capture some serious video footage from up above. With a flight time of about 10 minutes and an ultra-smooth ride, it’s a great introductory drone for anyone looking to […]
Don’t get handcuffed by Apple’s standard 3-foot Lightning cord (that you’ve most likely already lost), treat yourself to 10 feet of luxurious charging convenience. The Colossal is certified by Apple for its high-end quality, and designed to support full use of your phone while you power up. You can also get it in a 2-pack […]