Which hormone is primarily responsible for male characteristics and is produced by the testes?

Testosterone is the hormone primarily responsible for the development of male characteristics. It is produced in the testes and plays a crucial role in the development of male physical traits such as facial hair, deep voice, and muscle mass. Additionally, testosterone influences various physiological processes, including sperm production and libido. Its secretion begins significantly during puberty, leading to the maturation of male reproductive structures and the expression of secondary sexual characteristics.

In contrast, estrogen and progesterone are primarily associated with female reproductive functions, while oxytocin is linked to social bonding and reproductive behaviors, such as childbirth and lactation. Therefore, testosterone's specific role in male development and its production in the testes make it the correct answer to the question.