If we continue to consider the interrelationship of environment and genetics, the psychology text my foreign exchange student is reading has some interesting points about this dynamic. (This is the eight edition of this text, and has a publication date of 2007.) One particularly interesting segment discusses temperament:

An infant’s temperament is its emotional excitability—whether reactive, intense, and fidgety, or easygoing, quiet and placid. From the first weeks of life, difficult babies are more irritable, intense and unpredictable. Easy babies are cheerful, relaxed and predictable in feeding and sleeping. (Chess and Thomas, 1987)

• The most emotionally reactive newborns tend also to be the most reactive 9-month-olds (Wilson & Matheny, 1986; Worobey & Blajda, 1989).

• Four-month-olds who react to changing scenes with arched back, pumping legs, and crying are usually fearful and inhibited in their second year. Those who react with relaxed smiles are usually fearless and sociable in their second year (Kagan, 1990).

• The most emotionally intense preschoolers tend to be relatively intense as young adults (Larsen & Diener, 1987). In one ongoing study of more than 900 New Zealanders, emotionally reactive and impulsive 3-year-olds have developed into somewhat more impulsive, aggressive and conflict-prone 21-year-olds (Caspi, 2000).


Another line of evidence comes from physiological tests which reveal that anxious, inhibited infants have high and variable heart rates and a reactive nervous system, and that they become more physiologically aroused when facing new or strange situations (Kagan & Snidman, 2004).

While I completely agree that much of personality and temperament is genetic (I wouldn’t have understood this twenty years ago like I understand it now…) I find it interesting to superimpose the results of poor caregiving on top of the above statements. So a difficult baby becomes even more difficult if the caregiver is as irritable, intense and unpredictable as the child. And an easy baby can easily become a difficult one under abusive or neglectful circumstances. Or does the difficult baby become the more difficult child (full of rage, anger, aggression, etc.) and the easy baby become the shut down, flatliner child who just gives up?

Still more coming!

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