In addition to genetics and environment a child’s behavior may be influenced by their temperament. It is not uncommon that children in the same family who have similar genetic make up and have grown up in the same family environment will exhibit different behavioral responses in the same situation. “Temperament is normally used as a collective term for a set of developing traits that (1) manifest in an organized fashion during early life, (2) are relatively stable during significant periods of life, (3) are relatively consistent across situations, (4) have characteristic neurophysiologic underpinnings, and (5) are partially heritable."4
In 1977, Thomas and Chess proposed three categories of temperament or children; easy temperament, difficult temperament and slow-to-warm-up temperament.