1 Answers
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 ; through migration to the caudal end of the abdominal cavity ; migration just through the abdominal wall ; formation of a sub-anal swelling ; to the development of pronounced scrota in mammals.
Since 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. A scrotal location also exposes the testes to a reduced temperature below that of the body, which has been suggested to reduce the spontaneous rate of germ cell mutations.