Wikipedia

Baculum

(Redirected fromPenile bone)
Not to be confused withPenile spines.

Thebaculum(pl.:bacula), also known as thepenis bone,penile bone,os penis,os genitale,[1]oros priapi,[2]is abonein thepenisof manyplacental mammals.It is absent from thehuman penis,but present in the penises of someprimates,such as thegorillaand thechimpanzee.[3][4]The baculum arises from primordial cells in soft tissues of the penis, and its formation is largely influenced byandrogens.[5]The bone lies above theurethra,[6]and it aidssexual reproductionby maintaining stiffness duringsexual penetration.Thehomologueto the baculum infemale mammalsis the baubellum (os clitoridis), a bone in theclitoris.[7][8][9]

Baculum of adog's penis;the arrow shows the urethral sulcus, which is the groove in which the urethra lies.
Fossilbaculumof abear (Indarctos)from theMiocene

Etymology

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The wordbaculummeans "stick" or "staff" inLatinand originates fromGreek:βάκλον,baklon"stick".[10]

Function

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The baculum is used for copulation and varies in size and shape byspecies.Its evolution may be influenced bysexual selection,and its characteristics are sometimes used to differentiate between similar species.[11]A bone in the penis allows a male to mate for a long time with a female,[12][13][14]which can be a distinct advantage in somemating strategies.[15][16]The length of the baculum may be related to the duration ofcopulationin some species.[17][18]In carnivorans[19]and primates, the length of the baculum appears to be influenced bypostcopulatory sexual selection.[20]In somebatspecies, the baculum can also protect theurethrafrom compression.[21]

Presence in mammals

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A raccoon baculum

Mammals having a penile bone include variouseutherians:

It is absent in humans,ungulates(hoofed mammals),[33]elephants,monotremes(platypus,echidna),[34]marsupials,[35]lagomorphs,[25]hyenas,[36]binturongs,[26]sirenians,[6]andcetaceans(whales, dolphins, and porpoises),[6]among others.

Evidence suggests that the baculum was independently evolved 9 times and lost in 10 separate lineages.[26]The baculum is an exclusive characteristic of placentals and closely related eutherians, being absent in other mammal clades, and it has been speculated to be derived from theepipubic bonesmore widely spread across mammals, but notoriously absent in placentals.[35]

Among the primates,marmosets,[clarification needed]weighing around 500 grams (18 oz), have a baculum measuring around 2 millimetres (0.079 in), while the tiny 63 g (2.2 oz)galagohas one around 13 millimetres (0.51 in) long. The great apes, despite their size, tend to have very small penis bones, and humans are the only ones to have lost them altogether.[16]

In some mammalian species, such as badgers[37][38]and raccoons (Procyon lotor), the baculum can be used to determine relative age. If a raccoon's baculum tip is made up of uncalcified cartilage, has a porous base, is less than 1.2 g (0.042 oz) in mass, and measures less than 90 mm (3.5 in) long, then the baculum belongs to a juvenile.[28]

Absence in humans

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Unlike most primates, humans lack an os penis,[39][40]but the bone is present, although much reduced, among othergreat apes.In many ape species, it is a relatively insignificant 10–20 mm (0.39–0.79 in) structure. Cases ofhuman penisossification following trauma have been reported,[41]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.[42]Clellan S. FordandFrank A. BeachinPatterns 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 theerectionis provided entirely through blood pressure in thecorpora cavernosa.An "artificial baculum" orpenile implantis sometimes used to treat erectile dysfunction in humans.[43]

InThe Selfish Gene,Richard Dawkins[44]proposed honest advertising as the evolutionary explanation for the loss of the baculum. The hypothesis states that if erection failure is a sensitive early warning of ill health (physical or mental), females could have gauged the health of a potential mate based on his ability to achieve erection without the support of a baculum.

The tactile stimulation hypothesis proposes that the loss of the baculum in humans is linked to the female choice for tactilestimulation:a boneless penis would be more flexible, facilitating a larger range of copulatory positions and whole body movement, giving females greater general physical stimulation.[45]

The mating system shift hypothesis proposes that the shift towards monogamy as the dominant reproductive strategy may have reduced the intensity of copulatory and post-copulatory sexual selection, and made the baculum obsolete.[46][47]

Humans "evolved amating systemin which the male tended to accompany a particular female all the time to try to ensure paternity of her children "[16][better source 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 ofcopulationthat the baculum makes possible, thereby maximizing their chances of fathering the female's offspring. Human females exhibitconcealed ovulation,also known as hidden estrus, meaning it is almost impossible to tell when the female is fertile (unless the cervical mucus is examined),[48]so frequent matings would be necessary to ensure paternity.[16][49][50]

Strengths and weaknesses of these hypotheses were revised in a 2021 study, which also proposed an alternative hypothesis: that conspecific aggression, in combination with the development of self-awareness, may have played a role in the loss. If the presence of a baculum exacerbated the prevalence and severity of penile injuries resulting from blunt trauma to a flaccid penis, increasing ability to foresee the consequences of their actions would also enable hominins to realise that these injuries are a useful tool in male-male competition. This behavioural innovation, planned conspecific aggression with the goal of temporary exclusion of competitors from the breeding pool, would create an environment in which a genetic mutation for a penis without a baculum (or with an unossified baculum) would strongly increase the fitness of the mutant phenotype. Along with the hominin propensity for social learning and cultural transmission, this hypothetical scenario may explain why this phenotype became fixed in all human populations.[51]

An alternative view is that its loss in humans is an example ofneotenyduring human evolution; late-stage fetal chimpanzees lack a baculum.[52]

Cultural significance

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Walrus baculum, around 22 inches (56 cm) long

It has been argued that the "rib" (Hebrewצֵלׇעṣēlāʿ,also translated "flank" or "side" ) in the story ofAdam and Eveis actually a mistranslation of aBiblical Hebreweuphemism for baculum, and that its removal from Adam in theBook of Genesisis acreation storyto explain this absence (as well as the presence of theperineal raphe– as a resultant "scar" ) in humans.[53]

InHoodoo,the folk magic of theAmerican South,the raccoon baculum is sometimes worn as an amulet for love or luck.[54]

Oosik

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Oosik(Iñupiaq:usukoruzuk) is a term used inAlaska Native culturesto describe the bacula ofwalruses,seals,sea lionsandpolar bears.Sometimes as long as 60 cm (24 in), fossilized bacula are often polished and used as a handle for knives and other tools. Theoosikis a polished and sometimes carved baculum of these large northern carnivores.

Oosiksare also sold as tourist souvenirs. In 2007, a 4.5 ft-long (1.4 m) fossilized penis bone from an extinct species of walrus, believed by the seller to be the largest in existence, was sold for $8,000.[55]

United States CongressmanforAlaska,Don Young,was known for possessing an 18-inch walrusoosik,and once brandished it like a sword during a congressional hearing.[56]

See also

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References

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  52. ^Bednarik, R. G. (2011).The Human Condition.doi:10.1007/978-1-4419-9353-3.ISBN978-1-4419-9352-6.(page 134), cited by:
    Achrati, Ahmed (November 2014). "Neoteny, female hominin and cognitive evolution".Rock Art Research.31(1): 232–238.
    "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'"
  53. ^Gilbert, S. F.; Zevit, Z. (2001). "Congenital human baculum deficiency: The generative bone of Genesis 2:21-23".American Journal of Medical Genetics.101(3): 284–85.doi:10.1002/ajmg.1387.PMID11424148.
  54. ^Joanne O'Sullivan (1 March 2010).Book of Superstitious Stuff: Weird Happenings, Wacky Rites, Frightening Fears, Mysterious Myths & Other Bizarre Beliefs.Charlesbridge Publishing. p. 87.ISBN978-1-60734-367-7.Archivedfrom the original on 29 December 2015.Retrieved27 October2015.In thehoodoo (folk magic)tradition of theAmerican South,a raccoon penis bone (scientifically known as the baculum) is a lucky charm used to attract love. In some areas, it's boiled to remove any trace of the animal, and then tied to a red ribbon and worn as a necklace. In other areas, the bones were traditionally given to girls and young women bysuitors,and in still other places, the charms are worn by men. Earrings made fromcastraccoon penis bones became a fad in 2004, and celebrities such asSarah Jessica Parkerand Vanessa Williams were photographed wearing them.New Orleansgamblers are said to use the bones (also called coon dogs and Texas toothpicks) for luck.
  55. ^"Walrus penis sells for $8,000 at Beverly Hills action".AP.Archived fromthe originalon 6 November 2007.Retrieved30 August2007.
  56. ^"A brief history of Rep. Don Young's incendiary remarks. (All right, it's a long history.)".Washington Post.Archivedfrom the original on 5 December 2020.Retrieved18 March2021.

Further reading

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  • Gilbert SF, Zevit Z (July 2001). "Congenital human baculum deficiency: the generative bone of Genesis 2:21–23".Am. J. Med. Genet.101(3): 284–5.doi:10.1002/ajmg.1387.PMID11424148.
  • Clellan S., Frank A. Beach (1951).Patterns of Sexual Behavior.New York: Harper, and Paul B. Hoeber, Inc. Medical Books.ISBN978-0-313-22355-6.
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