Baculum

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Baculum of a dog's penis; the arrow shows the urethral sulcus, which is the groove in which the urethra lies. Armand de Montlezun Baculum Pyrenees.jpg
Baculum of a dog's penis; the arrow shows the urethral sulcus, which is the groove in which the urethra lies.
Fossil baculum of a bear (Indarctos) from the Miocene

The baculum (pl.: bacula), also known as the penis bone, penile bone, os penis, os genitale, [1] or os priapi, [2] is a bone in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the gorilla and the chimpanzee. [3] [4] The baculum arises from primordial cells in soft tissues of the penis, and its formation is largely influenced by androgens. [5] The bone lies above the urethra, [6] and it aids sexual reproduction by maintaining stiffness during sexual penetration. The homologue to the baculum in female mammals is the baubellum ( os clitoridis ), a bone in the clitoris. [7] [8] [9]

Contents

Etymology

The word baculum means "stick" or "staff" in Latin and originates from Greek : βάκλον, baklon "stick". [10]

Function

The baculum is used for copulation and varies in size and shape by species. Its evolution may be influenced by sexual 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] which can be a distinct advantage in some mating strategies. [14] [15] The length of the baculum may be related to the duration of copulation in some species. [16] [17] In carnivorans [18] and primates, the length of the baculum appears to be influenced by postcopulatory sexual selection. [19] In some bat species, the baculum can also protect the urethra from compression. [20]

Presence in mammals

A raccoon baculum Raccoonpenisbone.jpg
A raccoon baculum

Mammals having a penile bone include various eutherians:

It is absent in humans, ungulates (hoofed mammals), [32] elephants, monotremes (platypus, echidna), [33] marsupials, [34] lagomorphs, [24] hyenas, [35] binturongs, [25] sirenians, [6] and cetaceans (whales, dolphins, and porpoises), [6] among others.

Evidence suggests that the baculum was independently evolved 9 times and lost in 10 separate lineages. [25] 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 the epipubic bones more widely spread across mammals, but notoriously absent in placentals. [34]

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) galago has 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. [15]

In some mammalian species, such as badgers [36] [37] 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. [27]

Absence in humans

Unlike most primates, humans lack an os penis, [38] [39] but the bone is present, although much reduced, among other great apes. In many ape species, it is a relatively insignificant 10–20 mm (0.39–0.79 in) structure. Cases of human penis ossification following trauma have been reported, [40] 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. [41] 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. [42]

In The Selfish Gene , Richard Dawkins [43] 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 tactile stimulation: a boneless penis would be more flexible, facilitating a larger range of copulatory positions and whole body movement, giving females greater general physical stimulation. [44]

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. [45] [46]

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] [ 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 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 (unless the cervical mucus is examined), [47] so frequent matings would be necessary to ensure paternity. [15] [48] [49]

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. [50]

An alternative view is that its loss in humans is an example of neoteny during human evolution; late-stage fetal chimpanzees lack a baculum. [51]

Cultural significance

Walrus baculum, around 22 inches (56 cm) long Armand de Montlezun (1841-1914) Bacalum Morse.jpg
Walrus baculum, around 22 inches (56 cm) long

It has been argued that the "rib" (Hebrew צֵלׇע ṣēlāʿ, also translated "flank" or "side") in the story of Adam and Eve is actually a mistranslation of a Biblical Hebrew euphemism for baculum, and that its removal from Adam in the Book of Genesis is a creation story to explain this absence (as well as the presence of the perineal raphe – as a resultant "scar") in humans. [52]

In Hoodoo, the folk magic of the American South, the raccoon baculum is sometimes worn as an amulet for love or luck. [53]

Oosik

Oosik (Iñupiaq: usuk or uzuk) is a term used in Alaska Native cultures to describe the bacula of walruses, seals, sea lions and polar bears. Sometimes as long as 60 cm (24 in), 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 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. [54]

United States Congressman for Alaska, Don Young, was known for possessing an 18-inch walrus oosik, and once brandished it like a sword during a congressional hearing. [55]

See also

Related Research Articles

<span class="mw-page-title-main">Mammal</span> Class of animals with milk-producing glands

A mammal is a vertebrate animal of the class Mammalia. Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 29 orders.

<span class="mw-page-title-main">Primate</span> Order of mammals

Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers; and the simians, which include monkeys and apes. Primates arose 85–55 million years ago first from small terrestrial mammals, which adapted for life in tropical forests: many primate characteristics represent adaptations to the challenging environment among tree tops, including large brain sizes, binocular vision, color vision, vocalizations, shoulder girdles allowing a large degree of movement in the upper limbs, and opposable thumbs that enable better grasping and dexterity. Primates range in size from Madame Berthe's mouse lemur, which weighs 30 g (1 oz), to the eastern gorilla, weighing over 200 kg (440 lb). There are 376–524 species of living primates, depending on which classification is used. New primate species continue to be discovered: over 25 species were described in the 2000s, 36 in the 2010s, and six in the 2020s.

<span class="mw-page-title-main">Glans penis</span> End of the penis

In male human anatomy, the glans penis or penile glans, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and primary anatomical source of sexual pleasure. The glans penis is present in the male reproductive organs of humans and most other mammals where it may appear smooth, spiny, elongated or divided. It is externally lined with mucosal tissue, which creates a smooth texture and glossy appearance. In humans, the glans is located over the distal ends of the corpora cavernosa and is a continuation of the corpus spongiosum of the penis. At the summit appears the urinary meatus and at the base forms the corona glandis. An elastic band of tissue, known as the frenulum, runs on its ventral surface. In men who are not circumcised, it is completely or partially covered by a fold of skin called the foreskin. In adults, the foreskin can generally be retracted over and past the glans manually or sometimes automatically during an erection.

<span class="mw-page-title-main">Animal sexual behaviour</span> Sexual behavior of non-human animals

Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproductively motivated or non-reproductively motivated.

Canine reproduction is the process of sexual reproduction in domestic dogs, wolves, coyotes and other canine species.

A pseudo-penis is any structure found on an animal that, while superficially appearing to be a penis, is derived from a different developmental path.

<span class="mw-page-title-main">Human penis</span> Human male external reproductive organ

In human anatomy, the penis is an external male sex organ that additionally serves as the urinary duct. The main parts are the root, body, the epithelium of the penis including the shaft skin, and the foreskin covering the glans. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis. The urethra goes across the corpus spongiosum and ends at the tip of the glans as the opening, the urinary meatus. It is a passage both for excretion of urine and the ejaculation of semen.

<span class="mw-page-title-main">Body of penis</span> Part of the penis located outside of the pelvic cavity

The body or shaft of the penis is the free portion of the human penis that is located outside of the pelvic cavity. It is the continuation of the internal root, which is embedded in the pelvis and extends to the glans. It is made up of the two corpora cavernosa and the corpus spongiosum on the underside. The corpora cavernosa are intimately bound to one another with a dorsally fenestrated septum, which becomes a complete one before the penile crura. The body of the penis is homologous to the female clitoral body.

<span class="mw-page-title-main">Penis</span> Primary sexual organ of male animals

In many animals, a penis is the main male sexual organ used to inseminate females during copulation. Such organs occur in both vertebrates and invertebrates, but males do not bear a penis in every animal species.

<span class="mw-page-title-main">Erection</span> Physiological phenomenon involving the hardening and enlargement of the penis

An erection is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal, sexual attraction or libido, although erections can also be spontaneous. The shape, angle, and direction of an erection vary considerably between humans.

<span class="mw-page-title-main">Human penis size</span> Measurement of the human penis

Human penises vary in size on a number of measures, including length and circumference when flaccid and erect. Besides the natural variability of human penises in general, there are factors that lead to minor variations in a particular male, such as the level of arousal, time of day, ambient temperature, anxiety level, physical activity, and frequency of sexual activity. Compared to other primates, including large examples such as the gorilla, the human penis is thickest, both in absolute terms and relative to the rest of the body. Most human penis growth occurs in two stages: the first between infancy and the age of five; and then between about one year after the onset of puberty and, at the latest, approximately 17 years of age.

An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs externally, although there are exceptions. For many species in the animal kingdom, the male intromittent organ is a hallmark characteristic of internal fertilization.

<span class="mw-page-title-main">Foreskin</span> Retractable fold of skin which covers and protects the glans of the penis

In male human anatomy, the foreskin, also known as the prepuce, is the double-layered fold of skin, mucosal and muscular tissue at the distal end of the human penis that covers the glans and the urinary meatus. The foreskin is attached to the glans by an elastic band of tissue, known as the frenulum. The outer skin of the foreskin meets with the inner preputial mucosa at the area of the mucocutaneous junction. The foreskin is mobile, fairly stretchable and sustains the glans in a moist environment. Except for humans, a similar structure known as a penile sheath appears in the male sexual organs of all primates and the vast majority of mammals.

<span class="mw-page-title-main">Penile spines</span> Pointed structures on the penile glans and/or shaft

Many mammalian species have developed keratinized penile spines along the glans and/or shaft, which may be involved in sexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two or three points per spine (strepsirrhines). Penile spine morphology may be related to mating system.

<span class="mw-page-title-main">Mammalian reproduction</span> Most mammals are viviparous, giving birth to live young

Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.

<span class="mw-page-title-main">Non-reproductive sexual behavior in animals</span> Non-reproductive behavior in non-human animals

Animal non-reproductive sexual behavior encompasses sexual activities that non-human animals participate in which do not lead to the reproduction of the species. Although procreation continues to be the primary explanation for sexual behavior in animals, recent observations on animal behavior have given alternative reasons for the engagement in sexual activities by animals. Animals have been observed to engage in sex for social interaction bonding, exchange for significant materials, affection, mentorship pairings, sexual enjoyment, or as demonstration of social rank. Observed non-procreative sexual activities include non-copulatory mounting, oral sex, genital stimulation, anal stimulation, interspecies mating, and acts of affection, although it is doubted that they have done this since the beginning of their existence. There have also been observations of sex with cub participants, same-sex sexual interaction, as well as sex with dead animals.

<span class="mw-page-title-main">Evolution of primates</span> Origin and diversification of primates through geologic time

The evolutionary history of the primates can be traced back 57-90 million years. One of the oldest known primate-like mammal species, Plesiadapis, came from North America; another, Archicebus, came from China. Other similar basal primates were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene. Purgatorius is the genus of the four extinct species believed to be the earliest example of a primate or a proto-primate, a primatomorph precursor to the Plesiadapiformes, dating to as old as 66 million years ago.

<span class="mw-page-title-main">Human sperm competition</span> Form of sexual selection

Sperm competition is a form of post-copulatory sexual selection whereby male sperm simultaneously physically compete to fertilize a single ovum. Sperm competition occurs between sperm from two or more rival males when they make an attempt to fertilize a female within a sufficiently short period of time. This results primarily as a consequence of polyandrous mating systems, or due to extra-pair copulations of females, which increases the chance of cuckoldry, in which the male mate raises a child that is not genetically related to him. Sperm competition among males has resulted in numerous physiological and psychological adaptations, including the relative size of testes, the size of the sperm midpiece, prudent sperm allocation, and behaviors relating to sexual coercion, however this is not without consequences: the production of large amounts of sperm is costly and therefore, researchers have predicted that males will produce larger amounts of semen when there is a perceived or known increase in sperm competition risk.

<span class="mw-page-title-main">Copulation (zoology)</span> Animal sexual reproductive act in which a male introduces sperm into the females body

In zoology, copulation is animal sexual behavior in which a male introduces sperm into the female's body, especially directly into her reproductive tract. This is an aspect of mating. Many animals that live in water use external fertilization, whereas internal fertilization may have developed from a need to maintain gametes in a liquid medium in the Late Ordovician epoch. Internal fertilization with many vertebrates occurs via cloacal copulation, known as cloacal kiss, while most mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.

The os clitoridis is a bone inside the clitoris of many placental mammals. It is absent from the human clitoris, but present in the clitoris of some primates, such as ring-tailed lemurs and non-human great apes. However, in the latter case, the bone is greatly reduced in size. It is homologous to the baculum in male mammals.

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  48. ↑ "Scientists have answered one of the biggest questions people have about their penis". The Independent. 14 December 2016. Archived from the original on 19 August 2017. Retrieved 15 December 2016.
  49. ↑ "ABC - Science - Beasts - Evidence - Programme 1 - Godinotia". Australian Broadcasting Corporation . 29 April 2014. Archived from the original on 29 April 2014. Retrieved 23 November 2020.
  50. ↑ Jakovlić, Ivan (2021) “The Missing Human Baculum: A Victim of Conspecific Aggression and Budding Self-Awareness?” Mammal Review. https://doi.org/10.1111/mam.12237
  51. ↑ Bednarik, R. G. (2011). The Human Condition. doi:10.1007/978-1-4419-9353-3. ISBN   978-1-4419-9352-6. (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'"
  52. ↑ 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. PMID   11424148.
  53. ↑ 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. ISBN   978-1-60734-367-7. Archived from the original on 29 December 2015. Retrieved 27 October 2015. In the hoodoo (folk magic) tradition of the American 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 by suitors, and in still other places, the charms are worn by men. Earrings made from cast raccoon penis bones became a fad in 2004, and celebrities such as Sarah Jessica Parker and Vanessa Williams were photographed wearing them. New Orleans gamblers are said to use the bones (also called coon dogs and Texas toothpicks) for luck.
  54. ↑ "Walrus penis sells for $8,000 at Beverly Hills action". AP. Archived from the original on 6 November 2007. Retrieved 30 August 2007.
  55. ↑ "A brief history of Rep. Don Young's incendiary remarks. (All right, it's a long history.)". Washington Post. Archived from the original on 5 December 2020. Retrieved 18 March 2021.

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