Many mammalian species have developedkeratinizedpenile spines along theglans or shaft, which may be involved insexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two or three points per spine (strepsirrhines).[1] Penile spine morphology may be related tomating system.[2][3]
Felines, especially domestic cats, are well known for having penile spines. Upon withdrawal of a cat'spenis, the spines rake the walls of the female'svagina, which mayserve as a trigger for ovulation.[4][5] Many otherfelid species have penile spines, but they are relatively small injaguars andpumas, and do not occur inmargays.[6]
Penile spines are often found in primate species that formcopulatory plugs after mating.[20] Ingalagos, penile spines may form a "genital lock" during copulation.[21]
In contrast to chimpanzees, a common morphological variant found in humans calledhirsuties 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.[22][23] These are sometimes described as vestigial remnants of penile spines.[7] However, the relationship between the structures is still uncertain.[24]
When thehominin lineage split into the generaHomo andPan, a regulatory DNA sequence associated with the formation of small keratinized penile spines was lost in theHomo lineage. This simplification of penis anatomy may be associated with the sexual habits of humans.[25] In some species which retain full expression, penile spines contribute to increased sexual sensation and quicker orgasms.[26] AnhCONDEL (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.[25]
^Dixson, A. F. (1987). "Observations on the evolution of the genitalia and copulatory behaviour in male primates".Journal of Zoology.213 (3):423–443.doi:10.1111/j.1469-7998.1987.tb03718.x.