Sex at Dawn полностью

For example, some species have seminal fluid that forms a “copulatory plug,” serving to block the entrance of any subsequent sperm into the cervical canal. Species engaging in this type of sperm competition (snakes, rodents, some insects, kangaroos) typically wield penises with elaborate hooks or curlicues on the end that function to pull any previous male’s plug out of the cervical opening. Though at least one team of researchers reports data suggesting men who copulate frequently produce semen that coagulates for a longer time, copulatory plugs don’t appear to be in the human sexual arsenal.

Despite its lack of curlicues, the human penis is not without interesting design features. Primate sexuality expert Alan Dixson writes, “In primates which live in family groups consisting of an adult pair plus offspring [such as gibbons] the male usually has a small and relatively unspecialized penis.” Say what you will about the human penis, but it ain’t small or unspecialized. Reproductive biologist Roger Short (real name) writes, “The great size of the erect human penis, in marked contrast to that of the Great Apes, makes one wonder what particular evolutionary forces have been at work.” Geoffrey Miller just comes out and says it: “Adult male humans have the longest, thickest, and most flexible penises of any living primate.”¹ So there.

Homo sapiens: the great ape with the great penis!

The unusual flared glans of the human penis forming the coronal ridge, combined with the repeated thrusting action characteristic of human intercourse—ranging anywhere from ten to five hundred thrusts per romantic interlude—creates a vacuum in the female’s reproductive tract. This vacuum pulls any previously deposited semen away from the ovum, thus aiding the sperm about to be sent into action. But wouldn’t this vacuum action also draw away a man’s own sperm? No, because upon ejaculation, the head of the penis shrinks in size before any loss of tumescence (stiffness) in the shaft, thus neutralizing the suction that might have pulled his own boys back.² Very clever.

Intrepid researchers have demonstrated this process, known as semen displacement, using artificial semen made of cornstarch (the same recipe used to simulate exaggerated ejaculates in many pornographic films), latex vaginas, and artificial penises in a proper university laboratory setting. Professor Gordon G. Gallup and his team reported that more than 90 percent of the cornstarch mixture was displaced with just a single thrust of their lab penis. “We theorize that as a consequence of competition for paternity, human males evolved uniquely configured penises that function to displace semen from the vagina left by other males,” Gallup told BBC News Online.

It bears repeating that the human penis is the longest and thickest of any primate’s—in both absolute and relative terms. And despite all the bad press they get, men last far longer in the saddle than bonobos (fifteen seconds), chimps (seven seconds), or gorillas (sixty seconds), clocking in between four and seven minutes, on average.

The chimpanzee penis, meanwhile, is a thin, conical appendage without the flared glans of the human member. Nor is sustained thrusting common to chimpanzee or bonobo copulation. (But really, how much sustained anything can you expect in seven seconds?) So while our closest ape cousins may have us beat in the testicles department, they lose to the human penis on size, duration, and cool design features. Furthermore, the average seminal volume in a human ejaculate is about four times that of chimpanzees, bringing the total number of sperm cells per ejaculate within range of the chimp’s.