Many mammalian species have developed

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

ized penile spines along the

glans The glans (, plural "glandes" ; from the Latin word for "acorn") is a vascular structure located at the tip of the penis in male mammals or a homologous genital structure of the clitoris in female mammals. Structure The exterior structure ...

and/or shaft, which may be involved in

sexual selection Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...

. These spines have been described as being simple, single-pointed structures (

macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and (in one instance) Gibraltar. Macaques are principally ...

s) or complex with two or three points per spine (

strepsirrhines Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and southeast Asia. Colle ...

). Penile spine morphology may be related to

mating system A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to animals, the term describes which males and females mating, mate under which circumstances. Reco ...

Non-human mammals

Felines, especially domestic cats, are well known for having penile spines. Upon withdrawal of a cat's penis, the spines rake the walls of the female's

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

, which may serve as a trigger for ovulation. Many other

felid Felidae () is the family of mammals in the order Carnivora colloquially referred to as cats, and constitutes a clade. A member of this family is also called a felid (). The term "cat" refers both to felids in general and specifically to the dom ...

species have penile spines, but they are relatively small in

jaguar The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus '' Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the th ...

s and pumas, and do not occur in

margay The margay (''Leopardus wiedii'') is a small wild cat native to Central and South America. A solitary and nocturnal cat, it lives mainly in primary evergreen and deciduous forest. Until the 1990s, margays were hunted illegally for the wildlif ...

s. Penile spines in chimpanzees and mice are small surface projections made by the piling up of keratinized cell layers in the outermost skin surface.Hill, W.C.O. Note on the male external genitalia of the chimpanzee. ''Proc.Zool.Soc. Lond.'' 116, 129–132 (1946) They occur in

wombat Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about in length with small, stubby tails and weigh between . All three of the extant species are members of the family Vombatidae. They are adap ...

koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the womb ...

spotted hyena The spotted hyena (''Crocuta crocuta''), also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus ''Crocuta'', native to sub-Saharan Africa. It is listed as being of least concern by the IUC ...

s, fossas,

echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae . The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the ...

s, primates, bats, and several

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

species. Penile spines are often found in primate species that form

copulatory plug A mating plug, also known as a copulation plug, sperm plug, vaginal plug, or sphragis (Latin, from Greek σφραγίς ''sphragis'', "a seal"), is gelatinous secretion used in the mating of some species. It is deposited by a male into a female g ...

s after mating. In

galago Galagos , also known as bush babies, or ''nagapies'' (meaning "night monkeys" in Afrikaans), are small nocturnal primates native to continental, sub-Sahara Africa, and make up the family Galagidae (also sometimes called Galagonidae). They ar ...

s, penile spines may form a "genital lock" during copulation.

Humans

In contrast to chimpanzees, a common morphological variant found in humans called

hirsuties coronae glandis Pearly penile papules (PPP) are benign small bumps on the human penis. They vary in size from 1–4 mm, are pearly or flesh-colored, smooth and dome-topped or filiform, and appear in one or several rows around the corona, the ridge of the ...

, or pearly penile papules, are substantially larger, appear to be an outpocketing of both surface and underlying connective tissue layers, and lack the rich innervation seen in other animals.Agrawal, SK et al. Pearly penile papules: a review. ''Int. J. Dermatology'' 43:199-201 (2004) These are sometimes described as vestigial remnants of penile spines. However, the relationship between the structures is still uncertain.Penile spines versus pearly penile papules in humans
/ref> When the

hominin The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos) and in standard usage excludes the genus ''Gorilla'' (gorillas). The t ...

lineage split into the genera ''Homo'' and ''Pan'', a regulatory DNA sequence associated with the formation of small keratinized penile spines was lost in the ''Homo'' lineage. This simplification of penis anatomy may be associated with the sexual habits of humans. In some species which retain full expression, penile spines contribute to increased sexual sensation and quicker orgasms.Paleoanthropology, Genetics, and Evolution
/ref> An hCONDEL (highly conserved region of DNA that contains deletions in humans) located near the locus of the androgen receptor gene may be responsible for the loss of penile spines in humans.

Birds

The penises of some bird species feature spines and brush-like filaments.

References

External links

*{{commons category-inline, Penile spines Felidae anatomy Mammal male reproductive system Mammal penis Penis

Non-human mammals

Humans

Birds

See also

References

External links