Research has shown that culture and context-specific gender roles have a stronger influence on emotional expression than do biological factors. "Empirical evidence suggests that girls are socialized to be emotional, nonaggressive, nurturing, and obedient, whereas boys are socialized to be unemotional, aggressive, achievement oriented, and self-reliant. Peers continue this process as children develop and mature in effect constraining how, where, why, and with whom certain emotions are expressed".[1] One study suggests that people tend to exhibit more intense negative facial expressions in solitary conditions, and smile more when others are present.