Secondary sexual characteristics come about during puberty. These include body hair growth, especially pubic and underarm hair, and genital development. Under the effects of different levels of gonadal steroids, different traits develop. For instance, higher levels of androgens affect the Adam’s apple and deepen the voice, while higher levels of estrogen cause breast development (Bjorklund & Blasi, 2011).
Bjorklund, D. F., & Blasi, C. H. (2011). Child and Adolescent Development: An Integrated Approach. Cengage Learning.