Babies are born with distinctive characteristics that make certain developmental outcomes more likely. Parental behavior is, in part, a reaction to the child’s behavior (See “Parent, child, and reciprocal influences,” and “How people make their own environments“) and physical appearance (”Infant attractiveness predicts maternal behaviors and attitudes“). Every published report of a correlation between parental behavior and child outcome now contains a disclaimer admitting that the direction of effects is uncertain and that the correlation could be due in part to a child-to-parent effect (The Nurture Assumption, p. 27), a type of evocative gene–environment correlation.
Children share 50% of their genes with each of their biological parents, which means that for genetic reasons alone, children born with a predisposition to be timid (Galen’s Prophecy) are more likely to be raised by timid parents, and children born with a predisposition to be aggressive are more likely to be reared by aggressive parents.
Genetic influences can produce change as well as stability. An individual may have blond hair at age 5, brown hair at age 25, and no hair at age 75, and these changes are ordained by the genes. As we get older we become more like our parents because our parents, too, went through these changes. Longitudinal studies using genetically informative designs (”Genetic change and continuity from fourteen to twenty months“) have shown that genetic influences that affect behavior or adjustment at one age are not necessarily the same genetic influences that affect these variables at another age. There are genes that kick in early and genes that bide their time.
The outcome of many years of research on parent-training interventions by Rex Forehand: Parents found the training to be effective in improving their children’s behavior at home but not at school. Similar conclusions have been reached in regard to programs designed to improve the school adjustment and academic performance of children living in poverty: There is little evidence that parenting programs produce the hoped-for linkage between changed parent behaviors and improved child outcomes (”Does research support claims about the benefits of involving parents in early intervention programs?“).
Behavioral genetic studies estimate genetic and environmental influences on developmental outcomes by measuring pairs of siblings. The results of these studies are monotonously consistent, regardless of the outcome measure used and the kinds of sibling pairs who participate — twins or ordinary siblings, reared together or apart, biologically related or not. Genetic effects generally account for 35% to 65% of the variance among the participants, the effects of being reared in the same home account for 0 to 10%, and the balance remains unaccounted for (”Where is the child’s environment?“). With few exceptions, being reared in the same home does not make siblings of any kind more alike.
These results show not only that siblings are different but that the home environment has had little or no net effect on the measured outcomes. If being reared by conscientious parents, for example, tended to make children more conscientious, then 2 children reared by conscientious parents should, on average, both be more conscientious than 2 reared by careless parents. Therefore, 2 children reared in the same home should be significantly more alike in conscientiousness than 2 reared in different homes, which is exactly what the studies do not find (”Genes, environment, and personality“). The same results also rule out the possibility that being reared by conscientious parents makes children less conscientious on average. The bottom-line effect of the shared home environment on conscientiousness is not noticeably different from zero.
For alcoholism (”The behavioral genetics of alcoholism“) and criminal behavior, the evidence strongly suggests that the operative environmental influences are in the neighborhood, not in the home.
A major study was launched in 1987; its results are described in The Relationship Code. David Reiss studied 720 pairs of same-sex adolescent siblings (identical and fraternal twins and full, half and stepsiblings) over a 3-year period, from early to mid-adolescence. The adolescents’ behavior and adjustment, and the behavior of their parents, were judged by observers, the parents, and the adolescents themselves; these multiple sources of information were combined to produce measures of unusual reliability.
Virtually all correlations between parental behaviors and child outcomes were accounted for by genetic factors. The parents treated their children differently but they were reacting to genetic differences among the children, rather than causing the differences. The environment not shared by siblings was by far the largest (in many cases, the sole) nongenetic contributor to the adolescents’ behavior and adjustment, and the study eliminated all of the following as possible sources of nonshared environmental influence: “differential marital conflict about the adolescent versus the sib, differential parenting toward siblings, and asymmetrical relationships the sibs construct with each other.” Ruling out the last factor indicates that differences in age — that is, birth order — cannot account for the differences between siblings.
Developmentalists and behavioral geneticists alike have so far been unable to identify the important environmental influences on development, the sources of the nongenetic variation in personality and behavior.
Birth order effects are real, but they are tied to the context of the family. We ordinarily know the birth order only of people we are close to, and these are the people we are most likely to see with their parents and siblings. Birth order studies in which parents are asked to rate their children’s personalities, or adults are asked to compare themselves with their siblings, generally do yield significant birth order effects; studies that use other methods generally do not (”Context-specific learning, personality, and birth order“). In a study in which pairs of siblings were rated both by parents and by teachers, parents judged the older sibling to be more aggressive than the younger one, but teachers judged them to be about the same (”An adoption study of the etiology of teacher and parent reports of externalizing behavior problems in middle childhood“).
Family misfortunes have repercussions on children’s lives outside the home. A divorce, for example, often involves moving to a different residence, and moving disrupts the child’s life outside the family. Even when other demographic differences are controlled, children who have experienced frequent residential moves have higher rates of social, behavioral, and academic problems (”Mobility as a mediator of the effects of child maltreatment on academic performance” & “Impact of family relocation on children’s growth, development, school function, and behavior“). McLanahan and Sandefur (Growing up with a Single Parent) found that controlling for 2 factors — number of residential moves and differences in family income — can erase most of the differences in outcome between children reared in single-parent and two-parent families.
Because developed societies require very different behaviors in the home and in public (”Growing up in the post-modern age”), and people everywhere make distinctions between kin and nonkin (How the Mind Works), children behave differently in different contexts (”Studying temperament via construction of the Toddler Behavior Assessment Questionnaire“).
Children bring with them to adulthood the language and accent of their peers, not those of their parents. Evidence comes from studies of hearing children reared by deaf parents and of deaf children reared by hearing parents and from studies of the children of immigrants.
Derek Bickerton interviewed adults whose parents had immigrated to Hawaii around the turn of the last century. Though the parents came from all over the world and spoke a variety of languages, their adult offspring all spoke the same language — a creole, created in their childhood peer groups. No trace of their parents’ language or accent was detectable in their speech; the language of their peers had become their “native language.” The adults in these communities used a pidgin, not the creole, to communicate with each other.
Simon Baron-Cohen (”Do children with autism acquire the phonology of their peers?”) studied the accents of children and young adults with autism. These were the offspring of immigrants; their mothers spoke English with a foreign accent. The nonautistic siblings of these children spoke English without a foreign accent, but 83% of the children and young adults with autism had retained the foreign accent of their mothers. Baron-Cohen attributed this outcome to “a lack of the normal drive to identify with peers.”
Multivariate genetic analysis makes it possible to estimate how much genetic and environmental influences each contribute to the correlations found between behavior in different contexts. For example, children who are shy in one social context are not necessarily shy in others, but some children are shy in every context (”The Consistency and Concomitants of Inhibition“). Multivariate genetic analysis shows that the genetic component of shyness is responsible for the correlation across contexts; differences in shyness from one context to another are due primarily to environmental influences (”Continuity and change in infant shyness from 14 to 20 months“).
Interventions designed to teach parents better ways of dealing with their noncompliant children succeed in reducing the children’s coercive behavior at home but do not produce significant improvements in their behavior in school.
Infants who behave in a somber, subdued fashion in the presence of their depressed mothers behave normally in the presence of nondepressed caregivers; their subdued behavior is “specific to their interactions with their depressed mothers” (”Infants of depressed mothers show less ‘depressed’ behavior with their nursery teachers”). Secure attachments to one caregiver are not good predictors of secure attachments to another (”Prediction of infant-father and infant-mother attachment” & “Quality of infants’ attachments to professional caregivers“). Nor are secure attachments to parents good predictors of successful relationships with peers (”Maternal, teacher, and child care history correlates of children’s relationships with peers“). The quality of sibling relationships does not predict the quality of relationships with peers; sometimes the correlations are negative (”Compensatory patterns of support among children’s peer relationships“).
According to Irenäus Eibl-Eibesfeldt (Human Ethology), once children in hunter–gatherer and tribal societies have been weaned, they spend most of their time in the local play group. “Thus the child’s socialization occurs mainly within the play group.”
When children divide or are divided into two groups, preexisting differences between the groups are widened by contrast effects between groups and assimilation within them.
Thus, putting antisocial youth together for a group intervention is likely to make them more antisocial, a prediction that has recently been confirmed by Thomas J. Dishion (”When interventions harm”).
A boy’s status in his peer group is determined in part by his size. Small, slow-maturing boys generally have lower status (”An ethological study of dominance formation and maintenance in a group of human adolescents“). Studies have shown that children who are small for their age tend to have more than their share of psychological problems (”Academic and emotional difficulties associated with short stature”).
M.C. Jones (”The later careers of boys who were early or late maturing,” 1957) did a longitudinal study comparing males who were slow developers — smaller than most of their peers throughout childhood — with early developers. The two groups ended up almost equal in mean adult height, but there were significant differences in their adult personalities. The early developers were more dominant, relaxed, and poised; the slow developers were more impulsive, attention-seeking, and touchy.
“Socialization, Personality Development, and the Child’s Environments,” by Judith Rich Harris
