What hormone is primarily responsible for the development of female secondary sexual characteristics?

Estrogen is the primary hormone responsible for the development of female secondary sexual characteristics. These characteristics include breast development, the distribution of body fat, and the development of a wider pelvis. Estrogen plays a crucial role in regulating various functions associated with the female reproductive system and is essential for the onset of puberty and the maintenance of female reproductive health.

In the context of hormone functions, estrogen is pivotal because it not only aids in the development of secondary sexual traits but also influences the menstrual cycle and reproductive function. This hormone is produced mainly by the ovaries, and during puberty, increased levels of estrogen lead to the physical changes observed in females, which help distinguish them from males.

The other hormones listed have different primary functions in the body. Testosterone, while also critical for sexual development, is primarily associated with male characteristics and muscle mass. Progesterone primarily plays a role in regulating the menstrual cycle and maintaining pregnancy rather than in developing secondary sexual characteristics. Oxytocin, though important in childbirth and lactation, is not involved in the sexual differentiation noted with estrogen. Thus, estrogen's specific role in developing female secondary sexual characteristics makes it the correct answer to the question.