Cross-species evidence suggests that the onset of locomotion and explorations away from the mother early in life is associated with functional maturation of emotion-related neural circuitry and behavioral sensitivity to danger-alerting cues. In human infants, these developmental changes in emotion-processing may occur during the second half of the first year when infants begin to exhibit preferential attention to social signals of fear. My talk will discuss this argument by reviewing i) studies examining the neural bases and nature of infants' attentional bias towards social signals of fear; ii) studies that have begun to link genetic variations in brain function with fear-processing in human infants; and iii) preliminary data suggesting that individual variations in early perceptual biases towards emotional cues may be relevant for predicting typical and atypical emotional traits later in life.