Undescended testicles (UT), which is used synonymously with the term cryptorchidism, is characterized as the failure of either one or both testes and their associated structures to descend during ...

Seeking an answer, a useful first step is to trace the evolution of descended testes. Testes remain high up in the abdomen in egg-laying mammals (monotremes), but descend in all marsupials, ...

For example, testes never descend in birds, yet their average body temperature is even higher than in mammals. Furthermore, in some adult mammals, testes remain in the belly cavity, often in their ...