Coming from an evolutionary approach, Is the only purpose of a scrotum to regulate the temperature of the testes?
Knowing all mammals are warm blooded, shouldn't all mammals have testes in a scrotum?
Having descended testes is a derived characteristic within mammals; monotremes and the Afrotheria (including elephants) all retain the ancestral character state (Kleisner, et al., 2010)2. Among those mammals with descended testes, these can be ascrotal or scrotal. Testicular descent is hypothesized to have only occurred once within Mammalia, with the ascrotal Laurasiatheria. Descended ascrotal testes are found in cetaceans, phocid seals, hippos, tapirs, rhinos, and some bats. Descended scrotal testes are found in horses, pigs, camels, and Carnivora.
Since basal mammals would presumably have to regulate testicular temperature just as much as derived mammals, the temperature regulation hypothesis seems to not hold up. So the real question is: why have a scrotum? One hypothesis has to do with evolution of fast locomotion (e.g., galloping).
According to Frey (1991, 40)4:
Chance (1996)5 suggests that the temperature hypothesis might represent a secondary adaptation: