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. 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. 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. This vacuum pulls any previously deposited semen away from the ovum, thus aiding the sperm about to be sent into action. 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. Homo sapiens : the great ape with the great penis! 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.” So there. Primate sexuality expert Alan Dixson writes, “In primates which live in family groups consisting of an adult pair plus offspring 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. I will quote at length the case Ryan makes regarding the uniqueness of the human penis in Sex at Dawn:ĭespite its lack of curlicues, the human penis is not without interesting design features. The first point is in regard to the suite of features that Ryan argues testify “in support of ancestral promiscuity.” These being: “penis morphology, repeated thrusting movement, frequent non-reproductive sexual behavior, female multiple orgasm, female copulatory vocalization, etc.).” The second one (communal caregiving among foragers), I will save for a later date, to focus narrowly here on the first. Say what you will about animal penises but they’re a perfect example of how fascinating, diverse, and maybe a bit weird, nature truly is.He makes two main points here that I think are worth engaging with further. The more complex penises belong to primates like bushbabies and lemurs, who mate with many partners in their lifetime. Primates with simpler penises tend to be monogamous (only have one partner) or polygynous (mate with only a few partners). We are the only primate without a bone in the penis and have a relatively more simple structure. The size and shape of penises in primates vary too and compared to other animals, the human penis is actually rather dull. In fact, humans have a proportionately large penis size compared to their body size – but length is not everything (am I right?). The largest gorilla will only have a penis that is two and half inches long when erect. However, the penis size of many primates is much compared to the testes. To put that into perspective, a human’s testis is only 50 grams, so chimps have a testis that is 3 times that! This is a third of the size of its brain. To accommodate this increased level of sperm production, the chimpanzee’s testis is relatively large, at a weight of 150 to 170 grams. The more sperm produced, the more likely it is that the female’s offspring will have that chimp’s DNA (which is the main goal in all primates, and indeed many animals). This results in sperm competition whereby each of the males need to produce lots of sperm to outcompete the other males. What’s more, each of these females are only fertile about once or twice every four years! So, a large penis is not exactly necessary.Ĭhimpanzees are pretty promiscuous creatures with several males mating with one female whilst she is fertile. Silverback males own a group of three-four females, known as a harem, who are constantly either pregnant or breastfeeding. Whilst this may seem surprising, gorillas don’t need massive genitals given the sexual dynamics of this species. Did you know that male silverback gorillas weigh around 250 kilograms, but their penis and testes are only 10 grams? That’s equivalent to a vending machine having a testis the weight of 10 paperclips.
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