Penile spines

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Penile spines of a domestic cat

Throughout many mammal species, males have developed keratinized penile spines along the glans and/or shaft of their penis that 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 (prosimians).[1] Penile spine morphology may be related to mating strategy.

Non-human mammals

Felines, especially domestic cats, are well known for having penile spines. As with other cats' penises, the male lion's penis has spines which point backwards. Upon withdrawal of the penis, the spines rake the walls of the female's vagina, which may cause ovulation.[2]

Penile spines in chimpanzees and mice are small surface projections made by the piling up of keratinized cell layers in the outermost skin surface.[3][4]

Humans

In contrast to chimpanzees and mice, the common structures found in humans 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.[5][6] Thus, the relationship between the structures is still uncertain.[7]

In the primate line from which humans have evolved, a regulatory DNA sequence associated with the formation of small keratinized penile spines was lost. This simplification of penis anatomy may be associated with the monogamous mating habits of humans.[8] In species which retain the full expression of penile spines, penile spines contribute to sexual pleasure and quicker orgasms.[9]

Hirsuties coronae glandis, found in humans, are sometimes described as vestigial remnants of penile spines.[3]

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.[10]

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See also

  • Lion#Reproduction and life cycle
  • Cat#Reproduction

References

  1. ↑ Alan F. Dixson (26 January 2012). Primate Sexuality: Comparative Studies of the Prosimians, Monkeys, Apes, and Humans. Oxford University Press. ISBN 978-0-19-954464-6. Retrieved 27 September 2013. 
  2. ↑ Virginia Douglass Hayssen; Ari Van Tienhoven (1993). Asdell's Patterns of Mammalian Reproduction: A Compendium of Species-specific Data. Cornell University Press. ISBN 978-0-8014-1753-5. Retrieved 27 September 2013. 
  3. ↑ 3.0 3.1 Hill, W.C.O. Note on the male external genitalia of the chimpanzee. Proc.Zool.Soc. Lond. 116, 129–132 (1946)
  4. ↑ Murakami, R. A histological study of the development of the penis of wild-type and androgen-insensitive mice. J. Anat. 153, 223–231 (1987)
  5. ↑ Glicksman, JM and Freeman, RG. Pearly penile papules. A statistical study of incidence. Arch. Dermatol. 93:56-59 (1966)
  6. ↑ Agrawal, SK et al. Pearly penile papules: a review. Int. J. Dermatology 43:199-201 (2004)
  7. ↑ Penile spines versus pearly penile papules in humans
  8. ↑ Genetic losses contribute to human features
  9. ↑ Paleoanthropology, Genetics, and Evolution
  10. ↑ Gotea, V.; Visel, A.; Westlund, J. M.; Nobrega, M. A.; Pennacchio, L. A.; Ovcharenko, I. (2010). "Homotypic clusters of transcription factor binding sites are a key component of human promoters and enhancers". Genome Research 20 (5): 565–577. doi:10.1101/gr.104471.109. PMC 2860159. PMID 20363979. 
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