Evolution of descended testes in mammals information
Mammals are the only animals in which the testes descend from their point of origin into a scrotum. Concurrently, mammals are the only class of vertebrates to evolve a prostate gland starting with prostate evolution in monotreme mammals.
Testicular descent occurs to a variable degree in various mammals, ranging from virtually no change of position from the abdominal cavity (monotremes, elephants, and hyraxes); through migration to the caudal end of the abdominal cavity (armadillos, whales, and dolphins); migration just through the abdominal wall (hedgehogs, moles, seals); formation of a sub-anal swelling (pigs, rodents); to the development of pronounced scrota (primates, dogs, ruminants) in mammals.[1]
Since the descent of the testes into a scrotal pouch subjects the animal to enhanced risk of accidental damage and/or vulnerability from predators and rivals, presumably there must be some evolutionary adaptive advantage to testicular descent. It has been proposed that the scrotum may act as a form of sexual decoration.[2] A scrotal location also exposes the testes to a reduced temperature below that of the body,[3] which has been suggested to reduce the spontaneous rate of germ cell mutations.[4]
^Setchell B.P. (1978). The Mammalian Testis. Cornell University Press, Ithaca, New York.
^Portman, A. (1952). Animal Forms and Patterns, Faber & Faber, London.
^Moore C.R. (1923). On the relationship of the germinal epithelium to the position of the testis. Anatomical Record 34: 337-358.
^Ehrenberg L., von Ehrenstein G., Hedgram A. (1957). Gonad temperature and spontaneous mutation-rate in man. Nature 180: 1433-1434.
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