The social-developmental hypothesis is one of the major arguments for the impact of nurture on emotional expression. The social-developmental theory explains gender differences in emotion expression through emphasizing "children's active role in their development of gendered behavior" through learning by watching adults or through interactions with their parents and peers (Chaplin & Aldao, 2012).[9] This hypothesis points to the fact that infants are not born with the same differences in emotional expression and gender differences generally grow more pronounced as children age.