What is the primary function of the testis in male mammals?

The primary function of the testis in male mammals encompasses both the production of sperm and the production of testosterone, making the comprehensive option the most accurate choice.

The testes are responsible for spermatogenesis, the process of sperm production, which takes place in the seminiferous tubules. This is essential for reproduction, as sperm is required for fertilization of the female egg.

Additionally, the testes produce testosterone, the primary male sex hormone, which plays a crucial role in the development of male secondary sexual characteristics, such as increased muscle mass, growth of body hair, and deeper voice. Testosterone is also important for the regulation of sperm production itself and overall male reproductive health.

Although body temperature regulation is important for sperm production—since the testes must be kept at a slightly lower temperature than the body to optimize sperm health—this function is more of a supportive role rather than a primary function. Therefore, the significant roles of sperm production and testosterone synthesis justify the selection of the comprehensive answer.