Baculum
The baculum (also penis bone, penile bone, or os penis, os genitale[1] or os priapi[2]) is a bone found in the penis of many placental mammals. It is absent in the human penis, but present in the penises of other primates, such as the gorilla and chimpanzee.[3][4] The os penis arises from primordial cells within soft tissues of the penis, and its formation is largely under the influence of androgens.[5] The bone is located above the male urethra,[6] and it aids sexual reproduction by maintaining sufficient stiffness during sexual penetration. The homologue to the baculum in female mammals is known as the baubellum or os clitoridis, a bone in the clitoris.[7][8][9]
Unlike most other primates, humans lack an os penis or os clitoris;[10][11] however, this bone is present but much reduced among the great apes. In many ape species, it is a relatively insignificant Template:Convert structure. Cases of human penis ossification following trauma have been reported,[12] and one case was reported of a congenital os penis surgically removed from a 5-year-old boy, who also had other developmental abnormalities, including a cleft scrotum.[13] Clellan S. Ford and Frank A. Beach in Patterns of Sexual Behavior (1951), p. 30 say, "Both gorillas and chimpanzees possess a penile bone. In the latter species, the os penis is located in the lower part of the organ and measures approximately three-quarters of an inch in length."[4] In humans, the rigidity of the erection is provided entirely through blood pressure in the corpora cavernosa. An "artificial baculum" or penile implant is sometimes used to treat erectile dysfunction in humans.[14]
The loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is thought to be because humans "evolved a mating system in which the male tended to accompany a particular female all the time to try to ensure paternity of her children"[15]Template:Citation needed which allows for frequent matings of short duration. Observation suggests that primates with a baculum only infrequently encounter females, but engage in longer periods of copulation that the baculum makes possible, thereby maximizing their chances of fathering the female's offspring. Human females exhibit concealed ovulation also known as hidden estrus, meaning it is almost impossible to tell when the female is fertile, so frequent matings would be necessary to ensure paternity.[15][16]Template:Clarify
It has been speculated that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is a result of sexual selection by females looking for honest signals of good health in prospective matesTemplate:Citation needed. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variationTemplate:Citation needed. Poor erectile function portrays not only physical states such as age, diabetes, and neurological disorders, but also mental states such as stress and depression.[17]Template:Citation needed
A third view is that its loss in humans is an example of neoteny during human evolution; late-stage fetal chimpanzees lack a baculum.[18]
- ↑ Cite error: Invalid
<ref>tag; no text was provided for refs namedEvansLahunta2013 - ↑ MLA Dolle, P., et al. "HOX-4 genes and the morphogenesis of mammalian genitalia." Genes & Development 5.10 (1991): 1767–1776.
- ↑ Template:Cite book
- ↑ 4.0 4.1 Patterns of Sexual Behavior Clellan S. Ford and Frank A. Beach, published by Harper & Row, New York in 1951. Template:ISBN
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<ref>tag; no text was provided for refs namedPerrinWursig2009 - ↑ Template:Cite journal
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- ↑ Carrion, Hernan, et al. "A history of the penile implant to 1974." Sexual medicine reviews 4.3 (2016): 285–293.
- ↑ 15.0 15.1 Template:Cite web
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"In humans, neoteny is manifested in the resemblance of many physiological features of a human to a late-stage foetal chimpanzee. These foetal characteristics include hair on the head, a globular skull, ear shape, vertical plane face, absence of penal bone (baculum) in foetal male chimpanzees, the vagina pointing forward in foetal ape, the presence of hymen in neonate ape, and the structure of the foot. 'These and many other features', Bednarik says, 'define the anatomical relationship between ape and man as the latter's neoteny'"