Secrets of the penis: Shape and size

In ”Secrets of the Phallus: Why Is the Penis Shaped Like That?” Jesse Bering at Scientific American, confesses that he has spent his life wondering why the human penis is "such a peculiarly shaped device." Here are his observations:

1. “The erect human penis is especially large compared to that of other primates, measuring on average between five and six inches in length and averaging about five inches in circumference.” Our closest living relative, the chimp, is nowhere near as large, even at its most excited phase.

2. Only the human phallus has such a distinctive mushroom cap-type head/glans. “Chimpanzees, gorillas and orangutans have a much less extravagant phallic design, more or less all shaft.” Another unique attribute?

3. During sex, the penis swells inside the vagina and “occupies the vaginal tract, and with full penetration can even reach the woman’s cervix and lift her uterus.” So maybe size does matter after all.

4. Even though humans are relatively monogamous, especially when compared to other species, we weren’t always so loyal, which is why the human penis adapted to deal with competing sperm from other mates. The “semen displacement theory” suggests that the human penis is meant to deposit sperm as deep in the vagina as possible, outshooting sperm from other sexual partners, biology’s way of ensuring paternity.

5. Another way the human penis outsmarts the competition? By getting rid of the competition’s sperm. Human male “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.” Basically, the frenetic thrusting not only encourages the penis to ejaculate, but it also flushes out the sperm left behind by prior partners.

6.Men also thrust deeper and faster after being reunited with partners they haven’t seen in awhile, which leads scientists to conclude that men want to make sure their partners aren’t impregnated by the competition while they’re away.