But humans are also selected for creativity – we are highly innovative, imaginative apes. Females have an evolved interest in the size of a man's penis, which has been sexually selected for its size and shape. But a woman is not going to "put the size of a man's cock right out of her mind", because she can't. Women are as aware as men that to build a stable relationship you need trust, shared interests and the ability to keep each other amused. Women with choice are not all "obsessed with the size of a man's cock". Patriarchy, on the other hand, correlates with a lack of openly displayed female choice. Enthusiastic females initiate both hetero- and homosexual activity, particularly when aggression begins to surface, resulting in satisfied, contented and peaceful bonobos. When compared with patriarchal chimps, the matriarchal bonobo is a far more sex-oriented ape. Ancestral females would have experienced a sexual freedom denied in Western cultures today and it has been suggested that our ancestors went through a period of matriarchy and enhanced female choice. But the larger human penis suggests that hominids needed to keep females with choice sexually satisfied. Human testis size indicates that males evolved under conditions in which their sperm competed inside females, but perhaps not to the same extent as chimp sperm. The impressive 200kg (400lb) silverback gorilla does have the smallest penis and testes of all male apes, but his massive canines and biceps and his controlling, jealous temper allow him to intimidate and fight off potential competitors. Female chimps or bonobos in oestrus often mate with several different individuals, so males must reproductively compete in this way and larger testes will therefore confer greater reproductive fitness.īy contrast, female gorillas live in harems and don't often get a chance to exercise a choice between mates, though occasionally a female and a male from outside the group may risk it. The more sperm a male produces and ejaculates inside a female the greater the probability that one of his will fertilise the ovum. 4 In multi-male/multi-female groups, males must compete to reproduce and frequently the competition takes place inside the female reproductive tract. Why?Ĭorrelations can be found between primate mating systems and male genital anatomy. As a proportion of overall body size, chimp and bonobo testes are twice as large as human testes, whereas gorilla testes are half the size. Interestingly, while the human penis is the biggest of all the ape species in length and girth, both in absolute terms and as a proportion of body size, the human testes are not. It has even been theorised that bipedalism evolved in humans to allow the fashionably new, larger, flexible penis to be displayed to discerning females. This unique adaptation is thought to have been selected through female mate choice, and by the time Homo erectus arrived on the scene, the hominid penis was significantly longer, fatter and more bendy than our ape cousins'. 2 The human penis has evolved the unusual system of vasocongestion to achieve erection, making the erect organ far more flexible than that of other primate species. Most primates, including chimpanzees, have a penis bone and achieve erections through muscle contraction. Today, the average erect gorilla penis is 3cm (1.25 inches) long, the average chimp or bonobo penis comes in at around 8cm and the average human penis stands at around 13cm. Through the mechanism of sexual selection, this will have increased penis size and altered structure. 1 Female primates can experience multiple orgasms, and it has been theorised that ancestral hominid females sought out males who would sexually satisfy them. A lot of sex has taken place since then, and a significant proportion has been motivated by female choice between rival males. The origins of the primate sex drive go back more than 60m years to the late Mesozoic era when the first primate evolved.
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