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.
More than 800 American energy and Earth science researchers have signed a letter to Donald Trump outlining six steps they’re urging him to take to address human-caused climate change to protect “America’s economy, national security, and public health and safety.” The letter is accompanied by a public change.org petition to “Tell Trump To #ActOnClimate.” Here […]
James Delingpole is an invective-hurling anti-climate science columnist who has candidly admitted that he doesn’t bother to read scientific papers, calling himself a “an interpreter of interpretations.”
Kratom (previously) is a widely used herb that has been very effective in treating opioid withdrawal and other chronic, hard-to-treat conditions — it also became very controversial this year because the DEA decided, without evidence, to class it as a dangerous drug, and then changed its mind (unprecedented!) after a mass-scale petition that included interventions […]
These days, there’s definitely no shortage of touchscreen gloves available, but the key is finding ones that consistently work well. These iGloves Touchscreen Gloves are super reliable, and are on sale for just $11.99.Super comfortable and functional, these gloves will keep your hands warm and still let you use any touchscreen, from phones to tablets. The iGloves’ […]
The Black Friday Mac Bundle 2.0 is one of the Boing Boing Store’s best-selling Mac bundles yet, and it’s about to come to an end. If you don’t get your copy now, here’s what you’ll be missing:This bundle comes packing 9 top-rated Mac apps in one package, at the hugely discounted price of just $23.99. […]
The Boing Boing Store’s Gift Guide is full of ideas for pretty much anyone in your life like hipster ice cub trays, Xbox controllers, Halo Boards, and even diamond necklaces. As always, all products in the Boing Boing Store come at great discounts, too. Shop by price bucket starting at under $20. Under $20:Bloxx Jumbo Ice Trays […]