In all primates except modern humans, tarsiers, and some South American monkeys, the penis contains a small bone called the baculum, a typically mammalian character. The testes, with a few exceptions among the lemurs, in which they are withdrawn seasonally, lie permanently in the scrotal sac, to which they migrate from their intra-abdominal position some time before birth (in humans) or after birth (in nonhuman primates). There could be no more effective barrier to mating between different species than incompatibility of the male and female sex organs.Īmong the characteristics of the primate order as listed by the 19th-century zoologist George Mivart, the penis is described as “pendulous” and the testes as “scrotal.” In contrast to most other mammals (bats being the principal exception), the primate penis is not attached to the abdominal wall but hangs free. The functions of the individual organs of reproductive systems are fairly uniform throughout the primates, but, in spite of this physiological homology, there is a remarkable degree of variation in minor detail of organs between groups-particularly in the external genitalia, which, by their variation, provide a morphological basis for the reproductive isolation of the species. Reproductive system Male and female genitalia SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.But there are more interesting hypotheses where that came from. Human penises are the largest of all, for which Curnoe offers a few possible explanations: bipedal motion and upright posture allow men to advertise their penises (great) and attract mates in a way chimps and gorillas can't. Gorillas, on the contrary, are organized hierarchically, with one alpha male getting to mate with as many females as he likes - and so the species' males have comparatively smaller penises and smaller testicles. "Amazingly, the proportions of the male reproductive organs, especially the testicles, are a reflection of the way apes are organized socially along reproductive lines," Curnoe says in his video series, "How Did We Get Here?" "It all comes down to the competition between males and their sperm when they mate with females."Ĭhimpanzees, for instance, have medium-sized penises and large testicles, due to higher rates of competition for more sexually receptive females. It all has to do with evolution, according to evolutionary biologist Darren Curnoe. Human penises - whether they hover around the 5.16-inch-long global average in length or lean closer to the other sides of the bell curve - are generally notably larger than the penises of chimpanzees or gorillas. It's also, weirdly, a possible advantage human males have over other primates.
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