Magnetic imaging studies of heterosexual couples having sex reveal that during coitus, the typical penis completely expands and occupies the vaginal tract and with full penetration can even reach the woman’s cervix and lift her uterus. This, combined with the fact that human ejaculate is expelled with great force and over considerable distance (up to two feet if not contained), suggests that men are designed to release sperm into the uppermost portion of the vagina possible.
In an article published in the journal Evolutionary Psychology, Gallup and Rebecca Burch argue that “a longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity.”
This “semen displacement theory” is the most intriguing part of Gallup’s story. Since sperm cells can survive in a woman’s cervical mucus for up to several days, if she has more than one male sexual partner over this period of time, say within forty-eight hours, then the sperm of these two men are competing for reproductive access to her ovum.
So how did nature equip men to solve the adaptive problem of other men impregnating their sexual partners? The answer, according to Gallup, is that their penises were sculpted in such a way that the organ would effectively displace the semen of competitors from their partner’s vagina, a well-synchronized effect facilitated by the “upsuck” of thrusting during intercourse.
Specifically, the coronal ridge offers a special removal service by expunging foreign sperm. According to this analysis, the effect of thrusting would be to draw other men’s sperm away from the cervix and back around the glans, thus scooping out the semen deposited by a sexual rival.
Η επιστημη μιλησε. Ο πικερισμος στηριζεται αυστηρα στην επιστημη.
