Baculum

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"Os penis" redirects here. It is not to be confused with Os Pinos.
Baculum of a dog's penis; the arrow shows the urethral sulcus.
Fossil baculum of a bear from the Miocene.

The baculum (also penis bone, penile bone or os penis) 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.[1] The bone is located above the male urethra,[2] and it aids sexual intercourse by maintaining sufficient stiffness during sexual penetration. The female equivalent is the os clitoridis – a bone in the clitoris.[3][4]

Etymology[edit]

The phallic meaning of the term is unique to English; however, similar words exist in other languages with the same meaning, such as the Slovenian word bakulum. It is derived from a Latin term which meant cudgel, scepter, staff or stick. The phrase argumentum ad baculum exemplifies the Latin meaning.

Purpose[edit]

The baculum is used for copulation and varies in size and shape by species. Its characteristics are sometimes used to differentiate between similar species. A bone in the penis allows a male to mate for a long time with a female,[5] which can be a distinct advantage[clarification needed] in some mating strategies.[6]

The word baculum originally meant "stick" or "staff" in Latin. The homologue to the baculum in female mammals is known as the baubellum or os clitoridis or (though poor Latin) os clitoris.[7]

Presence in mammals[edit]

A raccoon baculum.

Mammals having a penile bone (in males) and a clitoral bone (in females) include various eutherians:

It is absent in humans, ungulates (hoofed mammals), elephants, monotremes (platypus, echidna), marsupials, lagomorphs,[citation needed] hyenas,[14] and cetaceans (whales, dolphins, and porpoises), among others.[citation needed]

Such a wide distribution among placental mammals suggests that the bone evolved early in the history of these mammals, and was subsequently lost in certain groups.

Among the primates the marmoset, weighing around 500g, has a baculum measuring around 2mm, while the tiny 63g galago has one around 13mm 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.[6]

In some mammalian species, such as the raccoon (Procyon lotor), the baculum can be used to determine relative age. If the baculum tip is made up of uncalcified cartilage, has a porous base, masses less than 1.2g, and measures less than 90mm long, then the baculum belongs to a juvenile male.[12]

Absence in humans[edit]

Unlike other primates, humans lack an os penis or os clitoris; however, this bone is much reduced among the great apes: in many ape species it is a relatively insignificant 10–20 mm structure. There are reported cases of human penis ossification following trauma,[15] and one reported case of a congenital os penis surgically removed from a 5 year old boy, who also had other developmental abnormalities, including a cleft scrotum.[16] Clellan S. Ford and Frank A. Beach in Patterns of Sexual Behavior (1953), 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."[1] In humans, the rigidity of the erection is provided entirely through blood pressure in the corpora cavernosa.

It has been speculated that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is 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"[6] 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.[6]

The evolutionary biologist[17] Richard Dawkins speculated in 1989 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 mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function betrays not only physical states such as diabetes and neurological disorders but mental states such as stress and depression.[18]

Cultural significance[edit]

The existence of the baculum is unlikely to escape the notice of pastoralist and hunter-gatherer cultures (see also below).

The raccoon baculum is sometimes worn as a charm for luck or fertility.[citation needed]

Oosik[edit]

Oosik is a term used in Native Alaska cultures to describe the baculum of walruses, seals, sea lions, and polar bears. Sometimes as long as 60 cm (2 ft), fossilized bacula are often polished and used as a handle for knives and other tools. The oosik is a polished and sometimes carved baculum of these large northern carnivores.

Oosiks are also frequently sold as souvenirs to tourists by Alaska Natives. In 2007 a 4.5-foot (1.4 m) long fossilized penis bone from an extinct species of walrus, believed by the seller to be the largest in existence, was sold for $8,000.[19]

Walrus baculum, approximately 22 inches (56 centimetres) long.

See also[edit]

References[edit]

Notes[edit]

  1. ^ a b Patterns of Sexual Behavior Clellan S. Ford and Frank A. Beach, published by Harper & Row, New York in 1951. ISBN 0-313-22355-6
  2. ^ a b William F. Perrin; Bernd Wursig; J. G.M. Thewissen (26 February 2009). Encyclopedia of Marine Mammals. Academic Press. pp. 68–. ISBN 978-0-08-091993-5. 
  3. ^ Harold Burrows (1945). Biological Actions of Sex Hormones. Cambridge University Press. p. 264. Retrieved 4 August 2012. 
  4. ^ R. F. Ewer (1973). The Carnivores. Cornell University Press. ISBN 978-0-8014-8493-3. Retrieved 16 December 2012. 
  5. ^ Dixson, A. F. "Baculum length and copulatory behaviour in carnivores and pinnipeds (Grand Order Ferae)." Journal of Zoology 235.1 (1995): 67-76.
  6. ^ a b c d "Godinotia". Walking With Beasts. ABC — BBC. 2002. pp. Question: How do we know how Godinotia (the primate in program 1) mated?. Retrieved 29 June 2010. 
  7. ^ Best; Granai (2 December 1994). "Tamius merriami" (PDF). Mammalian Species (American Society of Mammalogists) 476: 1–9. doi:10.2307/3504203. 
  8. ^ Harkness, John E.; Turner, Patricia V.; VandeWoude, Susan; Wheler, Colette L. (2 April 2013). Harkness and Wagner's Biology and Medicine of Rabbits and Rodents. John Wiley & Sons. ISBN 978-1-118-70907-8. 
  9. ^ a b R. F. Ewer (1973). The Carnivores. Cornell University Press. ISBN 978-0-8014-8493-3. Retrieved 16 December 2012. 
  10. ^ Dyck, Markus G.; Bourgeois, Jackie M.; Miller, Edward H. (2004). "Growth and variation in the bacula of polar bears (Ursus maritimus) in the Canadian Arctic". Journal of Zoology 264 (1): 105–110. doi:10.1017/S0952836904005606. 
  11. ^ Howard E. Evans; Alexander de Lahunta (7 August 2013). Miller's Anatomy of the Dog. Elsevier Health Sciences. ISBN 978-0-323-26623-9. 
  12. ^ a b Nova J. Silvy (7 February 2012). The Wildlife Techniques Manual: Volume 1: Research. Volume 2: Management 2-vol. Set. JHU Press. ISBN 978-1-4214-0159-1. 
  13. ^ Baryshnikov, Gennady F., Olaf RP Bininda-Emonds, and Alexei V. Abramov. "Morphological variability and evolution of the baculum (os penis) in Mustelidae (Carnivora)." Journal of Mammalogy 84.2 (2003): 673-690.
  14. ^ Richard Estes (1991). The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores, Primates. University of California Press. pp. 323–. ISBN 978-0-520-08085-0. Retrieved 12 December 2012. 
  15. ^ Sarma, Deba; Thomas Weilbaecher (1990). "Human os penis". Urology 35 (4): 349–350. doi:10.1016/0090-4295(90)80163-H. PMID 2108520. 
  16. ^ Champion, RH; J Wegrzyn (1964). "Congenital os penis". Journal of Urology 91: 663–4. PMID 14172255. 
  17. ^ Ridley, Mark (2007). Richard Dawkins: How a Scientist Changed the Way We Think : Reflections by Scientists, Writers, and Philosophers. Oxford University Press. p. 228. ISBN 0-19-921466-2. , of page 228
  18. ^ Dawkins, Richard (2006) [1978]. The Selfish Gene (30th anniversary ed.). Endnote to 30th anniversary edition: Oxford University Press. p. 158 endnote. ISBN 0-19-929114-4. "It is not implausible that, with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male’s health, and robustness of his ability to cope with stress, from the tone and bearing of his penis." 
  19. ^ "Walrus penis sells for $8,000 at Beverly Hills action". AP. Archived from the original on 6 November 2007. Retrieved 30 August 2007. 

General references[edit]

  • 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. PMID 11424148. 
  • Clellan S., Frank A. Beach (1951). Patterns of Sexual Behavior. New York: Harper, and Paul B. Hoeber, Inc. Medical Books. ISBN 0-313-22355-6. 

External links[edit]