Many mammalian species have developed
keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. It is the key structural material making up Scale (anatomy), scales, hair, Nail (anatomy), nails, feathers, horn (anatomy), horns, claws, Hoof, hoove ...
ized penile spines along the
glans or shaft, which may be involved in
sexual selection
Sexual selection is a mechanism of evolution in which members of one 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 the opposite sex ...
. 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 Europe (in Gibraltar). Macaques are principally f ...
s) or complex with two or three points per spine (
strepsirrhines).
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
A penis (; : penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation (zoology), copulation, and through which male placental mammals and marsupials also Urination, urinate.
The term ''pen ...
, the spines rake the walls of the female's
vagina
In mammals and other animals, the vagina (: vaginas or vaginae) is the elastic, muscular sex organ, reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The #Vag ...
, which may
serve as a trigger for ovulation.
Many other
felid
Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ).
The 41 extant taxon, extant Felidae species exhibit the gre ...
species have penile spines, but they are relatively small in
jaguar
The jaguar (''Panthera onca'') is a large felidae, cat species and the only extant taxon, living member of the genus ''Panthera'' that is native to the Americas. With a body length of up to and a weight of up to , it is the biggest cat spe ...
s and
pumas, and do not occur in
margays.
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 of the family Vombatidae that are native to Australia. Living species are about in length with small, stubby tails and weigh between . They are adaptable and habitat tolerant, and are ...
s,
koala
The koala (''Phascolarctos cinereus''), sometimes inaccurately called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the Family (biology), family ''Phascolar ...
s,
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,
,
s,
primates,
bats,
and several
rodent
Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
species.
Penile spines are often found in primate species that form
copulatory plugs after mating. In
galagos, 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, 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 (hominins) form a taxonomic tribe of the subfamily Homininae (hominines). They comprise two extant genera: ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos), and in standard usage exclude the genus '' Gorilla'' ( gorillas) ...
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.[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.
See also
* Fordyce spots
* Sexual conflict#Spiky genitals
* Lion#Reproduction and life cycle
References
External links
*{{commons category-inline, Penile spines
Felidae anatomy
Mammal male reproductive system
Mammal penis
Penis