Perspectives on two temperamental biases.

This paper describes the contribution of two infant temperamental biases to variation in behaviour and biology over the first 18 years in a sample of middle-class Caucasian children. One bias, called high reactive, is defined by frequent display of limb activity and crying in four-month-old infants to unexpected or unfamiliar events. The other, called low reactive, is defined by the opposite pair of behaviours to the same incentives. High reactive infants are likely to display cautious, avoidant responses and signs of an excitable amygdala to unexpected experiences. Low reactives are characterized by a sociable, emotionally spontaneous profile to the same experiences and a minimally excitable amygdala. However, each bias is a better predictor of the future traits that are unlikely to develop than the ones that do. The final pattern of traits is a function of the person's temperaments, life history, and current circumstances.This article is part of the theme issue 'Diverse perspectives on diversity: multi-disciplinary approaches to taxonomies of individual differences'.