The Nurture Assumption: Why Children Turn Out the Way They Do

In her Introduction to the second edition (2009), Harris reflects on how experts and non-experts received the first edition in 1998. She reports many people were surprised and offended by her assertion that peers, not parents, are the primary influence in child socialization. She laments media coverage of her work, which painted her as believing parents do not matter. Harris claims parents do matter, but still believes they have “no lasting influence on their children’s personalities or on the way they behave outside the home” (xvii). While some viewed this argument as “heretical,” others were intrigued or supportive (xvii).

Harris also addresses questions and clarifies claims made in the first edition of her work. In hindsight, she feels she conflated socialization with personality development: Now, she claims socialization is children’s adaptation to their culture, while personality development comprises differences between individuals. Harris clarifies her term “peer group” does not refer to a specific group of friends, but a “social category” such as “girl.” Her group socialization theory begins with children ages two to three, and accelerates as a child grows and socializes with peers. She believes this theory applies to children everywhere but cannot be fully proven; however, “the nurture assumption” is also unproven.

In recent years, scientists have proven the role of genetics in shaping human development. Harris believes this supports her theory that when children resemble their parents, it is their genes, not parenting, which is responsible for similarities. She reiterates that social scientists have yet to fully prove parental influence, and laments the “anxiety-ridden, labor-intensive style of parenting” that has become the norm (xxii).

Psychologists consider nature and nurture the two forces that impact human development. According to some, parents are wholly responsible for how their children develop because they supply both nature (genes) and nurture (environment). Harris argues using the word “nurture” as a synonym for “environment” obscures other influences on human development. She claims psychologists who conflate nurture, environment, and parenting perpetuate the nurture assumption. She seeks to deconstruct this assumption and provide new ideas about child development.

Harris blames Austrian neurologist Sigmund Freud for the nurture assumption, as he theorized adult psychological issues are rooted in one’s childhood and parents. In the 1940s-1950s, a new school of thought in psychology emerged—“Behaviorism.” In Freudian tradition, Behaviorists focused on how parents condition their children through specific responses and rewards: They argued children are malleable, and that nurture is more important than nature. Harris laments Freudian and Behaviorist framing of parenting as a primary influence, as most psychologists and socialization researchers accept this view and structure research around specific practices. The nurture assumption persists in spite of studies that prove otherwise: For example, in the 1950s, American psychologist Eleanor Maccoby’s study of hundreds of four-year-olds could not establish any link between parenting practices and the children’s personalities.

Harris previously authored textbooks on child development but doubted the quality of contemporary research based on personal observations. For example, her Russian American landlords knew little English, but their children were fluent and exhibited more American mannerisms. Harris refutes the idea that children imitate their parents, particularly parents of the same gender. In fact, much of adult life is barred from children. Parents are important to children as their first caregivers and teachers—however, Harris disagrees with the notion that this early parenting creates later patterns.

Harris contrasts socialization researchers interested in nurture and behavioral geneticists interested in nature. These two groups of researchers generally disagree about child development and rarely read each other’s work. Socialization researchers cannot perform controlled experiments because they cannot raise children in a lab environment. Instead, they gather and analyze data for correlations. Harris argues it is difficult to draw conclusions from correlational data, but researchers and the media often do so. For example, socialization researchers may correlate a stimulating home and a child’s intelligence by counting the books in a child’s home and measuring their IQ: They would then check “if the children who live in homes with lots of books have high IQs and if the children who live in homes with no books have low IQs” (17). The higher a correlation, the more statistically significant it is. As some correlations are due to chance, researchers take findings more seriously when they are repeated in different studies.

Harris acknowledges two trends in research: The first is that parents with well-managed lives and relationships tend to have children who grow up to have these things, while the inverse is true; the second trend is that children who are parented with respect and affection tend to thrive more than the inverse. With this in mind, most researchers believe parenting is the primary influence in child development. However, Harris posits related studies have not distinguished between parents’ genes and decisions. Behavioral geneticists often study adopted children to investigate the role of genes in human development; specifically, these studies often compare adopted children to adopted or biological siblings. Behavioral geneticists have generally found that of the variations in people’s personalities, 50% can be attributed to genes and 50% to environment. However, this 50-50 split does not apply to every individual case: For example, if a farmer saved seeds from their sweetest corn, the next year’s crop would have the same sweetness due to their inherited genes. However, their sweetness would still vary due to environmental factors such as each plant’s soil, water, and sun exposure. This example illustrates that “it is possible for heredity to account for 100 percent of the resemblance between parent and offspring even though it accounts for only 50 percent of the variation among the offspring” (23).

Harris argues parenting is always a “two-way street” because people parent differently depending on the needs and personality of each of their children, who are born with innate differences. Researchers tend to portray parents as “types,” but in reality, parents generally don’t have a set teaching style. Harris recalls her own mother cautioning her while reassuring her timid son, to illustrate how children’s differences inform how they are parented. She also uses these examples to question the value of researchers’ generalizations. For example, if kind children are hugged more by their parents, this may be because parents show more affection to pleasant children, and not that children are pleasant because they are hugged more.

Direct genetic effects are “straightforward consequences” of one’s genes, such as physical appearance, while indirect genetic effects are the “effects of the effects of the genes” (28). For example, a child’s genes may make him handsome, causing parents and peers to give him more affection. Because study methods can’t distinguish between direct and indirect genetic effects, Harris considers both direct and indirect genetic effects as part of one’s heredity—rather than one’s environment. With that said, she reiterates socialization researchers have done a poor job of proving parenting is the most important factor in human development.

Twin-related studies and anecdotal stories in particular have raised questions about the role of genes in human development. For example, there are many stories about twins separated at birth and reunited as adults who find they share personality traits, preferences, and mannerisms. If parenting does play a significant role in determining personality, then identical twins raised in the same household should be more alike than those raised apart. However, this is not the case: Data reveals being raised in the same household increases differences amongst siblings.

Harris credits socialization researchers Eleanor Maccoby and John Martin with honestly engaging with the data in their field. Maccoby and Martin concluded such data suggests parenting decisions either had little to no impact on children’s characteristics, or that parents varied their parenting from child to child. Harris herself summarizes: “either the home and the parents have no effects, or else the only things that have effects are those that differ for each child in the family. The first alternative would mean that the nurture assumption is wrong” (37). It seems likely that parents create “microenvironments” that differ for each child by treating them differently, but researchers need to prove parents do so for their own reasons and not because of a child’s innate differences. They must also prove different treatment has a lasting effect on a child.

It is commonly believed that parents treat children differently based on birth order. However, Harris cites a 1980 review by Swiss academic Jules Angst and psychiatrist Cecile Ernst that found no connection between birth order and personality. Angst and Ernst then conducted their own study of over 7,000 people and still could not connect personality traits—such as extraversion and introversion—to birth order. Additionally, a 1990 review by British psychologist Judy Dunn and American British psychologist Robert Plomin didn’t identify any personality patterns based on birth order. Harris claims this means that even if parents treat their children differently, variations in parenting don’t have a lasting effect.

In her own work, socialization researcher Diana Baumrind labeled three parenting styles—Authoritarian, Permissive, and Authoritative—claiming authoritative parenting produced more positive results in children. Harris questions these results, noting related data merely indicates a trend in authoritative parents producing well-behaved children. It is unclear if this parenting style produces good children, or if these children are innately cooperative. Thus, Harris accuses these studies of cultural bias, noting Asian and African American parents are more likely to be authoritarian, but their children are not more likely to have problems.

Harris goes on to consider parenting decisions which create concrete differences between families, and how this may affect children. For example, no notable differences have been found between the children of working mothers and those of stay-at-home mothers; going to daycare or staying at home also does not produce notable differences, and neither does being raised by parents of the same sex or different sex, or being an only child. Thus, Harris urges experts to consider alternative explanations.