This chapter examines the emergence of the gender gap in depressive disorders at puberty, and to compare alternative theories as to the factors that underpin gender differentiation in depression at this developmental stage. The gender intensification hypothesis suggests that gender role orientations become more differentiated between the sexes over the adolescent years, as a result of exacerbated gender socialisation pressures during this time. The social-risk hypothesis of depression suggests that depressed mood evolved to facilitate a risk-averse approach to social interaction in situations where individuals perceive their social resources to be at critically low levels. Sexual selection has been used to understand the emergence of sex differences in a variety of areas of human behaviour. Research on sex differences in social cognition has supported the prediction that females are more sensitive to the negative social implications of information.