Scientific reason behind why testes located in the scrotal sac because in testes sperm are produced. Sperm need an optimum temperature to form properly. The testes being located outside the body enable the whole system regulate temperature. Sperm production works best at temperatures slightly lower than body temperature. The scrotum allows for some regulation. When it's cold, the testes are pulled in close to the body. If it is hot, they hang real low.
