Evolution_of_descended_testes_in_mammals
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]