Harris wrote a book called The Nurture Assumption, and more recently No Two Alike, that both took a similar line, suggesting that the influence of the home environment is relatively small in shaping a child’s personality.
She bases this on research suggesting that children can and do adapt their behaviour according to whether they’re with their parents, with others, in the home, or otherwise.
Harris suggests that child behaviours that remain the same across various environments are more likely to be influenced by genetics.
In other words, she argues that the idea we relate to others in specific ways because we’ve learnt certain core relationship styles with our parents is mistaken, and in fact, we develop context and person specific relationship patterns that can be seen even from an early age.
She gives the example of the classic distinction made between the personalities of first and last born children:
Firstborns and laterborns do behave in characteristic ways when they’re in the presence of their parents and siblings, but they drop these behaviours when they’re away from their family. Like James in [TV programme] Child of our Time, they adapt their behaviour to their setting. The firstborn who dominates his younger siblings at home doesn’t automatically assume that he will also be able to dominate his classmates. After all, even though he’s the largest child at home, he may turn out to be the smallest one in the playground. Research confirms that firstborn children are, on average, no more dominant in the playground than are laterborns. Nor do laterborns go through life permanently cowed. A laterborn who is pushed around by his older brother at home is fully capable of stepping into a dominant role with his peers.