Baculum

A raccoon baculum.

The baculum (also penis bone, penile bone or os penis) is a bone found in the penis of most mammals. It is absent in humans, equids, marsupials, lagomorphs, hyenas, and cetaceans (whales, dolphins, and porpoises) among others. It is used for copulation and varies in size and shape by species. Its characteristics are sometimes used to differentiate between similar species. The oosik of Native Alaskan cultures is a polished and sometimes carved baculum of various large northern carnivores such as walruses. The raccoon baculum is sometimes worn as a charm for luck or fertility.^[1]

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 os clitoris.

Presence in mammals

Penis bone (Os penis) of a dog, arrow shows the urethral sulcus.

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

• Order Primates, although not in humans.
• Order Rodentia (rodents), though not in the related order Lagomorpha (rabbits, hares etc)
• Order Insectivora (insectivores, including moles, shrews, and hedgehogs)
• Order Carnivora (including members of many well-known Families, such as Ursids (bears), Felids (cats), Canids (dogs), Pinnipeds (Walruses, Seals, Sea Lions), Procyonids (Raccoons etc), Mustelids (Otters, weasels, skunks) and others
• Order Chiroptera (bats)

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.

Absence in humans

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,^[2] 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.^[3] Clellan S. Ford and Frank A. Beach, Patterns of Sexual Behavior, p. 30 says "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." In humans, the rigidity of the erection is provided entirely through blood pressure in the corpus cavernosum.

The evolutionary biologist Richard Dawkins speculated in 2006 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 signs 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.^[4]

In another context, it has been speculated that Adam's "rib" mentioned in the Eden narrative of Creation really refers to the baculum. The Hebrew term translated as "rib" (tsela`) can also mean "side", "chamber", as well as any strut-like supporting structure, e.g. a beam or a tree trunk. The existence of the baculum is unlikely to escape the notice of pastoralist and hunter-gatherer cultures (see also below), but there is no specific term for it – nor for the penis itself – in Biblical Hebrew.^[5]

Oosik

Oosik is a term used in Alaska 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. It is also frequently sold as a souvenir to tourists by Alaska Natives, the only people permitted to hunt the walrus today. 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.^[6]

Walrus baculum, approximately 22 inches (56 centimetres) long

References

Notes

General references

• Gilbert, Scott F. and Ziony Zevit. 2001. Congenital human baculum deficiency: The generative bone of Genesis 2:21–23. American Journal of Medical Genetics 101(3): 284–285.
• Clellan S. And Frank A. Beach 1951 Patterns of Sexual Behavior Publisher: N.Y., Harper, and Paul B. Hoeber, Inc. Medical Books (ISBN 0313223556)

External links

• Beresford WA, Burkart S. The penile bone and anterior process of the rat in scanning electron microscopy. J Anat. 1977 Dec;124(3):589–97.
• The San Diego Zoo's Conservation and research for endangered species projects. 'What is the significance of the baculum in animals?'