Which hormone is associated with a deepened voice, muscle development, and increased competitiveness and aggression?

• A. Estrogen
• B. Cortisol
• C. Insulin
• D. Testosterone

Answer: (D)

Testosterone is the hormone most closely tied to the traits described—deepening of the voice, increased muscle mass, and heightened competitiveness and aggression. During puberty, rising testosterone drives the development of male secondary sexual characteristics, including a deeper voice and greater muscle growth. It also influences behavior in ways that can include increased drive for dominance and competitive activity, though the exact expression depends on context and individual differences. Testosterone is produced mainly in the testes, with smaller amounts from the adrenal glands in both sexes, and levels rise during adolescence to shape these physical and behavioral changes. The other hormones don’t fit as well: estrogen governs other aspects of development and female-typical traits, cortisol is about stress responses rather than muscle growth or baseline aggression, and insulin regulates metabolism and energy rather than secondary sexual characteristics.