Judith Rich Harris (2009) defines the nurture assumption as "the assumption that what influences children's development, apart from their genes, is the way their parents bring them up" (p. 2). Socialization researchers have purportedly shown that "there are good child-rearing styles and bad child-rearing styles" and that "parents who use a good child-rearing style" have "better children than those who use a bad child-rearing style" (p. 16). Although it's true that there are strong correlations between parenting styles and behavior in children, correlation should not be confused with causation. Harris points out that almost every parent-child dyad in these studies are biological relatives and that these studies do not separate the effects of heredity and environment (p. 20). Consequently, it's not clear whether these children turn out as they do because of environmental or genetic factors.
To answer this question, behavioral geneticists have studied the psychological traits and cognitive abilities of identical twins and unrelated adoptive siblings. Research has found the following:
- Identical twins separated early in life have striking similarities.[1]
- Identical twins raised in the same home are not much more similar than those raised in different homes.
- Unrelated adoptive siblings "are no more similar to each other than any two unrelated children chosen at random from a population" (Workman & Reader, 2014, location 4144).[2]
Genes, it turns out, "account for 50 percent of the variation among people and the shared environment between 0 and 10 percent." It therefore follows that the non-shared environment must account for about 40 percent of the variation found among people (Workman & Reader, 2014, locations 4144-4161).[3] Harris claims that the influence of other children primarily accounts for this 40 percent of variation. She refers to this theory as group socialization theory.
Group Socialization Theory: Preliminary Evidence
Four Observations
Harris writes that three observations led her to group socialization theory. (1) Immigrant children. Though adults who emigrate remain very foreign -- e.g., in terms of language, accent, culture, etc. -- their children tend to quickly assimilate. They speak the new language without an accent and in virtually every way seem little different than native born children. (2) Upper-class British males. The sons in such families spend little time with their parents: until the age of eight they're primarily with the nanny, and then they go off to boarding school and only spend the holidays at home. And yet these boys grow up to sound and act like their upper-class fathers, not their nannies or teachers. (3) Children. The nurture assumption states that children become socialized by imitating their parents, but in fact socialization consists of learning that you're not supposed to act like your parents, as parents do all sorts of things that children would get in trouble for imitating.
She later discusses a fourth observation which seems to lend support to group socialization theory: (4) Deaf-hearing dyads. Hearing children born to deaf parents become "fluent speakers of English" (p. 66). Conversely, deaf children born to hearing parents learn sign language from their peers, even when their parents don't know it, even when they don't learn it in school, even when they are in fact beaten from using it (pp. 180-185).
More Evidence: Different Settings, Groupishness
To set up her argument, Harris discusses two well-established human phenomena.
First, people behave differently in different social settings. Douglas Detterman writes that "there is no convincing evidence that people spontaneously transfer what they learned in one situation to a new situation, unless the new situation closely resembles the old one" (p. 54).[7] The evidence for this is as follows.
(1) "Developmentalist Carolyn Rovee-Collier and her colleagues have done a series of experiments on the learning ability of young babies. The babies lie in a crib, looking up at a mobile hanging above them. A ribbon is tied to one of their ankles in such a way that when they kick that foot, the mobile jiggles. Six-month-old babies catch on to this very quickly: they are delighted to discover that they can control the mobile’s movements by kicking their foot. Moreover, they will still remember the trick two weeks later. But if any detail of the experimental setup is changed—if a couple of the doodads hanging from the mobile are replaced with slightly different doodads, or if the liner surrounding the crib is changed to one of a slightly different pattern, or if the crib itself is placed in a different room—the babies will gaze up at the mobile cluelessly, as though they had never seen such a thing in their lives.8 Evidently babies are equipped with a learning mechanism that comes with a warning label: what you learn in one context will not necessarily work in another" (p. 54).
(2) "Researchers have studied how toddlers behave at home (by asking their mothers to fill out questionnaires) and at day-care centers (by observing them there or by asking the caregivers at the center) and found that the two descriptions of the children’s behavior do not agree. 'There exists the possibility that the toddler’s actual behavior differs systematically in the home and day-care settings,' admitted one researcher" (p. 56).
(3) One researcher concluded that "[f]ew significant associations were found between measures of children’s sibling relationships and characteristics of their peer relationships...Children who were observed to be competitive and controlling to their siblings were reported by their mothers to have positive friendships. Children whose mothers reported that they had hostile sibling relationships received higher scores on friendship closeness...Indeed, we should not expect competitive and controlling behaviour toward a younger sibling to be necessarily associated with negative and problematic behaviour with friends" (p. 57).
(4) "You would think a picky eater in one setting would be a picky eater in another, wouldn’t you? Yes, it has been studied, and no, that’s not what the researchers found. One-third of the children in a Swedish sample were picky eaters either at home or in school, but only 8 percent were picky in both places" (p. 58).
(5) One study found that children who behave obnoxiously with their parents are much less likely to behave that way with their peers and vice versa. "The correlation between obnoxious behavior in the two settings was only .19, which means that if you saw how a child behaved with her parents you would be unlikely to predict correctly how she would behave with her peers" (p. 59). This conclusion shouldn't be surprising: "A child who acts cute and babyish for her daddy evokes a different reaction from her classmates. Children who get laughs for their clever remarks at home wind up in the principal’s office if they don’t learn to hold their tongue in school. At home the squeaky wheel gets the grease; outside, the nail that sticks up gets hammered down" (p. 54).
(1) In the 1950s some social psychologists took 22 boys who had never before met and divided them into two groups at a summer camp in Robbers' Cave State Park, Oklahoma. Each group initially believed they were the only occupants at the camp but then one day "the two groups heard each other playing in the distance and both immediately wanted to show the others ‘who was boss.'" (Workman & Reader, location 5537). When the psychologists "brought together to play a series of games, competition soon spilled over into aggression and violence. Name-calling quickly progressed into physical fighting and, while between-group hostility was spiralling out of control, individual boys were seen to act in defence of other group members. The only thing that relieved the hostility was the introduction of an imaginary third group," as the psychologists "told the boys that a group of unknown boys from outside the camp had been vandalising the camp water system and that both groups were needed to check the entire water pipeline. This, and a number of other tasks that required the collaboration of the two groups, gradually led to a truce between them. Despite this armistice, the boys remained closer to their group members than to those of the other group" (location 5537).[5]
(2) A 1970s study reviewed how quickly and arbitrarily people divide into groups. In this study, a group of teenage boys was asked to watch as a series of dots were flashed across a screen. Each boy was then individually taken into another room and told whether he was an "underestimator," meaning that he underestimated the number of dots, or an "overestimator," meaning that he overestimated the number of dots. In fact, these labels were randomly assigned. Each boy was then asked how much money should be rewarded to his peers, but his peers were only identified by number and group. "For example, a boy who had just been told that he was an overestimator would be asked to check off...how much money should be given to 'member No. 61 of the overestimator group' and how much to 'member No. 74 of the underestimator group.' Whatever he checked off -- this was clearly stated in the instructions -- it would not affect his own payment" (Harris, p. 119). The boys "gave more money to the member of their own group than to the members of the other. They seemed to be as motivated to underpay the members of the other group as to overpay the members of their own" (p. 119).
Harris make several key points about groups, which can be summarized as follows.
(a) As we've seen, people naturally and easily form groups with others.
(b) People form groups with individuals they perceive as being like themselves. People have a natural tendency to form groups with like individuals. People marry those like themselves, people befriend those like themselves, etc.[6] If salient similarities exist, people will tend to form groups based on those similarities. In the absence of salient similarities, people will identify other, less salient, similarities: e.g., if "you live in the same state, you voted the same way in the last election, you are the same age or sex, you came to camp on the same bus, you are stuck in the same elevator" (p. 131).
(c) People identify most strongly with a particular group when a competing group is salient. For instance, I'm more likely to categorize myself as an adult when children are present and less likely in a roomful of adults; the Rattlers clung to their identity as Rattlers when they learned that other boys were sharing the campground with them (p. 132). "In the absence of a common enemy, or of a common goal that can be achieved only if everyone pulls together, groups tend to fall apart into a collection of individuals or smaller groups" (p. 133).
(d) When a competing group is salient, the the differences between groups increase while the differences within the groups decrease. Harris points out that at Robbers Cave, "the Rattlers liked to think of themselves as tough -- not a bunch of sissies. An Eagle was permitted (by his fellow Eagles) to cry if he twisted an ankle or bloodied a knee, but a Rattler was expected (by his fellow Rattlers) to bear up stoically. Children’s groups use various methods, often quite cruel, to enforce their unspoken rules of behavior. Those who will not or cannot conform to the rules, or who are different in any way, may be excluded, or picked on, or made fun of" (p. 124).
(e) People feel compelled to conform to group norms. This point was illustrated by a series of experiments conducted in the 1950s by Solomon Ash. "A typical experiment began with eight young men showing up at the laboratory, supposedly to take part in a study of perceptual judgments. Only one of the eight was actually a subject, however—the others were confederates of the researcher, trained to perform a role. Their role was to sit around a big table with the gull—er, the subject—and give incorrect perceptual judgments out loud, with a straight face. They were to show no sign of amusement or surprise when the subject’s judgments disagreed with what they had been told to say. Not all subjects gave in to their desire to conform; in fact, the majority continued to give correct responses even when all seven of the others were aligned against them. The point of these experiments was not to show that people will cave in under the threat of public humiliation: it was to show that a person will question the evidence of his own eyes before he will question the unanimous opinion of his peers. The subject didn’t accuse the others of lying or of conspiring against him (though in fact they were). He didn’t think there was anything wrong with the other guys—he thought there was something wrong with him. 'I began to doubt that my vision was right' was a typical comment" (pp. 124-125).
More Evidence: Peer Pressure
Harris proceeds to provide evidence that peer pressure is extraordinarily powerful.
(1) "Developmentalist Thomas Kindermann studied some cliques in a fifth-grade classroom and found that children who belonged to the same cliques had similar attitudes toward schoolwork. Well, that’s not too surprising: the kids probably belonged to the same cliques because they had similar attitudes. But in fifth grade, cliques haven’t solidified yet -- children can still move into them or out of them. This gave Kindermann the opportunity to study what happens when a kid moves into or out of a clique of academic achievers. What he found was that children’s attitudes toward schoolwork change if they switch from one group to another over the course of a school year. If a child moves into a clique of academic achievers, her attitude toward schoolwork is likely to improve; if she moves out of it, her attitude gets worse. Kindermann’s findings demonstrate that children’s attitudes toward achievement are influenced by their group affiliations. The changes he measured could not have been due to changes in the children’s intelligence or in their parents’ attitudes, since neither is likely to reverse direction over the course of a single school year" (p. 170).
(2) "British studies have shown that when delinquent London boys move out of the city their delinquency rates decline -- even if they move with their families. By living in one neighborhood rather than another, parents can raise or lower the chances that their children will commit crimes, drop out of school, use drugs, or get pregnant" (pp. 198-199).
(3) One study found: "When African American youths and white youths were compared without regard to neighborhood context, African American youths were more frequently and more seriously delinquent than white youths. When African American youths did not live in underclass neighborhoods, their delinquent behavior was similar to that of the white youths" (p. 199).
(4) "A developmentalist named Leann Birch noticed that children of preschool age—an age notorious for its picky eaters—cannot be cajoled by their parents into eating foods they dislike, or think they dislike. Parental propaganda and persuasion don’t work; the child remains intransigent. There is only one way to get a preschooler to learn to like a disliked food: seat her at a table with a group of children who do like it and serve it to all of them" (p. 154).
Clarification
Criticism
Workman & Reader (2014) write that Harris' claim "that parents have little or no long-lasting effect is only partially borne out by the data." They write:
The data seem to show that growing up in the same parental environment does not seem to make children any more similar to one another (e.g. Plomin and Daniels, 1987) but this does not show that parents have no effect. In fact, although parents seem to think that they tend to treat all of their children the same, this is neither the view of their children, nor is it the view of independent observers who have rated parental behaviour to different offspring (Reiss et al., 2000). Put simply, parents treat different children differently so parental behaviour would contribute to the non-shared rather than the shared environment (Plomin, 2011). So parents might have an effect, they just don’t have the effect of making siblings more like each other.
Other researchers have proposed that because the results show no effect of the shared environment; there must be an interaction between parental behaviour and children’s personalities (Vandell, 2000). Interaction is used here in the statistical sense which means that the effect of a particular variable (in this case parental behaviour) is dependent upon another variable (in this case the child’s genetic make-up). A particular parental behaviour would therefore have an effect on each individual child but because each child responds in a different way the effect cancels out when summed across many children. For instance, permissive parenting might cause some children to become irresponsible because there are no constraints on their behaviour, and others to become ultra-responsible because they have to assume control over their own lives. Each form of behaviour is having an effect, but when you add the individual effects together they cancel each other out so it looks like there is no effect of the shared environment (see Pinker, 2002). Such an effect is unlikely but by no means impossible and might still rescue the notion that parents have a long-lasting effect on children. So far, however, there is little evidence to support the claim that parental effects are truly interactive. (locations 4211-4225)
Workman & Reader that Harris' claim that one's development is largely influenced by one's peers might be true but has yet to be proven. They write:
There is evidence that attitudes, values and other culturally specific behaviours such as accent are strongly influenced by the peer group rather than parents, but the mechanisms by which peer groups can influence variation in personality is harder to explain. One way that Harris suggests this could happen is that siblings might join different peer groups, with perhaps one child joining a group of children who are responsible and hard working and the other joining a group of anti-establishment slackers. In order for this to work, however, the motivation to join each group must not be on the basis of genetic propensities; if it were, the effects of the peer group would show up as effects on the genes. To see why, remember that heritability estimates do not differentiate between the direct effect of the genes (e.g. genes that ‘code’ for assertiveness) and the indirect effects of the genes (genes that ‘code’ for attractiveness that leads to assertiveness because of the way people treat them). If group membership were just an indirect effect of the genes it would therefore show up as an effect of genes, rather than an effect of the unique environment, which is what we are trying to explain. So we are looking for an effect that would essentially drive identical twins apart on a variety of personality traits. Harris’s other suggestion is that the roles within a particular peer group – whether you are a leader, joker, peacemaker or the butt of everyone’s jokes – might have this effect. This might work because there may be competition for particular roles which might mean, in the case of identical twins, that one twin might be the leader, with the other forced into some other role (because there can be only one leader). Harris acknowledges that there is little evidence to support this particular mechanism but it seems that the environmental influence on children might be more capricious and dependent on chance than might at first be thought. Pinker (2002) proposes that chance events throughout life – being in the right place at the right time, or vice versa; catching an illness; minor differences in the uterine environment or subtle variations in brain chemistry when the brain is being wired up – might ultimately explain why identical twins are different, and thereby account for the effect of the unique environment on us all (see chapter 13).
Ultimately Harris’s theory may be proved wrong or too extreme, perhaps the null effect of shared environment might be genuinely due to interactions between parental behaviour and children’s personalities. Whatever is the case we must ensure that the effects of the genes are taken into account when studying socialisation and development and that the effects of nurture are no longer merely assumed, but tested directly. (locations 4209-4247)
What Parents Can Do
"Parents have some power to impart any aspect of their culture that involves things done in the home; cooking is a good example. Anything learned in the home and kept at home -- not scrutinized by the peer group -- may be passed on from parents to their kids" (p. 311). Kids will retain knowledge, skills, or opinions acquired at home if they are in an area "that the peer group regards as optional -- an area where conformity is not enforced, where differences may even be appreciated." "Most children's peer groups permit their members to vary in their talents, hobbies, political preferences, and future career plans." What kids don't learn at home "is how to behave in public and what sort of people they are. These are things they learn in the peer group" (p. 311).
Parents can determine a child's peers -- by moving to a certain neighborhood, picking a different school. Put your kid in a school with "smart, hardworking kids. A school where no one makes fun of the one who reads books and makes A's." E.g., Midwood High in Brooklyn. (Read NY Times story.) Kids at Midwood don't divide into two competing groups, pro-school and anti-school. You also might want to move if your kid is getting bullied, as kids get bullied partly because they get the reputation as someone who is bullied.
The problem w/ giving your child high self-esteem -- it doesn't carry over, as kids with high self-esteem at home don't have high self-esteem in general (p. 320). "Self-esteem in general -- the kind that travels well -- is a function of one's status in one's group. School-age children are aware of how they compare with their classmates and how they are regarded by them. Low status in the peer group, if it continues for long, leaves permanent marks on the personality" (p. 320). Parents can help their children's status in their peer group by such means as the following: "make them look as normal and attractive as possible, b/c looks do count. 'Normal' means dressing the child in the same kind of clothing the other kids are wearing. 'Attractive' means things like dermatologists for the kid with bad skin and orthodontists for the one whose teeth come in crooked...Even giving a kid a weird or silly name can put him at a disadvantage" (p. 321).
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Notes
[1] Harris writes: "Tales of the eerie resemblances between identical twins separated early in life and reared in different homes have made their way into the popular press and the popular imagination. There was the story of the two Jims -- both bit their nails, enjoyed woodworking, drove the same model Chevrolet, smoked Salems, and drank Miller Lite; they named their sons James Alan and James Allan. There was the story in my local newspaper, accompanied by a photo of two men with the same face, both wearing fire helmets -- reunited because both had become volunteer firefighters. There was the story of Jack Yufe and Oskar Stöhr, one reared in Trinidad by his Jewish father, the other in Germany by his Catholic grandmother. When reunited, they were both wearing rectangular wire-frame glasses, short mustaches, and blue two-pocket shirts with epaulets; both were in the habit of reading magazines back to front and flushing toilets before using them; both liked to startle people by sneezing in elevators. And there was the story of Amy and Beth, adopted into different homes -- Amy a rejected child, Beth doted upon -- both girls suffering from the same unusual combination of cognitive and personality deficits" (p. 31)
[2] See Plomin et al., 1994; Plomin and Daniels, 1987; and Turkheimer, 2000. Harris summarizes research showing that the following factors do not seem to effect the way children turn out: birth order (pp. 38-42), parenting style (pp. 42-46), maternal employment (p. 47), daycare attendance (p. 47), unconventional family environment (pp, 47-48), being an only child (p. 48), the nature of sibling relationships (pp. 56-58).
[3] This genetic effect is a mixture of direct genetic effects and indirect genetic effects, indirect genetic effects being "the effects of the effects of the genes" (Harris, p. 28). For instance, "people judged to be attractive are generally more assertive, a finding that is explained by the observation that attractive people are generally treated with more deference than less attractive people. Even if there were no direct genetic influence on assertiveness we can see that there is an indirect one; genes influence attractiveness which leads to individuals being treated differently, which affects their personality" (Workman & Reader, 2014, location 4097; see also location 4124).
[4] This tendency makes perfect sense from an evolutionary perspective: "For many millions of years (long before our own species stepped onto the stage) primates have been living in groups. For all that time—all but the last little bit of it—the individual’s survival depended on the survival of the group, and the members of the group were close relatives. A willingness to die for others who carry your genes makes sense in evolutionary terms. Many animals do things that appear to be self-sacrificing -- the bird squawks to alert its fellows, though its squawk may make it the predator’s target -- because even if they die, their sisters and brothers, their children and parents, might be saved. The individual may be lost but the genes it shares with its kin are preserved and passed on...In a human hunter-gatherer group, everyone was related to everyone else, either by blood or by marriage. Human groups no longer consist solely of people who are related to each other, but the motivator that powers group behavior doesn’t seem to know that. Underneath the embellishments provided by our recently acquired cognitive abilities are deep evolutionary roots. The emotional power of groupness comes from a long evolutionary history in which the group was our only hope of survival and the members of the group were our sisters and brothers, our children and parents, our husbands and wives" (pp. 129-130).
[5] One important lesson of this study is that "if we want to resolve group conflict then one way to do so is by presenting a common enemy" (location 5549).
[6] Married couples tend to resemble one another in numerous ways, including "race, religion, socioeconomic class, IQ, education, attitudes, personality characteristics, height, breadth of nose, and distance between the eyes" (p. 131). Similarities are also found among friends; for instance, "[i]n grade school, children who are good friends are likely to be of the same age, sex, and race, and to have similar interests and values" (p. 131).
[7] Detterman writes that this a tendency that might have evolved because "undergeneralization may be more adaptive than overgeneralization," as it is "safer to assume that a new situation has new rules, and that one must determine what the new rules are, than to blithely forge ahead under the assumption that the old rules are still in effect" (p. 54).
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Harris, J. R. (2009). The nurture assumption: Why children turn out the way they do [Kindle version]. Retrieved from Amazon.com.
Plomin, R., Chipuer, H. M., & Neiderhiser, J. M. (1994). Behavioral genetic evidence for the importance of nonshared environment. In E.M. Hetherington, D. Reiss and R. Plomin (eds). Separate social worlds of siblings: The impact of nonshared environment on development (1-31). Hillsdale, NJ: Lawrence Erlbaum.
Turkheimer, E. (2000). Three laws of behavior genetics and what they mean. Current directions in psychological science, 9(5), 160-164.
Workman, L., & Reader, W. (2014). Evolutionary psychology: An introduction [Kindle version]. Retrieved from Amazon.com.
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