Harris's most famous work,
The Nurture Assumption, was first published in 1998, with a revised version published in 2009. In this book, she challenges the idea that the personality of adults is determined chiefly by the way they were raised by their parents. She looks at studies which claim to show the influence of the parental environment and claims that most fail to control for genetic influences. For example, if aggressive parents are more likely to have aggressive children, this is not necessarily evidence of parental example; it may also be that aggressiveness has been passed down through the genes. She also points out that correlations between parent and child personalities may result as easily from child-to-parent effects as the reverse. As part of her presentation, she also argues against Frank Sulloway's theory of the effects of
birth order. The book looks to influences outside the home as the primary socializing agents of children, with peers being particularly important in personality development. Harris argues that children identify with their classmates and playmates rather than their parents and other adults, and that personality is formed both through efforts to fit in with the group or to compete with specific others. ==
No Two Alike==