Kathryn Asbury

Why are children in the same family so different? Nonshared environment a decade later.

Objective: To review recent developments in the study of nonshared environment; that is, the environmental influences that make children growing up in the same family different, rather than similar. Method: We review several recent influential books and papers on the subject of nonshared environment from the decade following the 1987 paper that highlighted its importance in psychological development. Results: Modest progress has been made toward identifying the specific aspects of the environment responsible for nonshared environment. Although parents treat their multiple children differently, such differential treatment accounts for only a small amount of nonshared environmental influence, once genetic factors are controlled. It has been suggested that some degree of nonshared environment may be due to the fact that siblings react differently to ostensibly shared environmental influences. Peer influence and other experiences outside the family may be more important sources of systematic nonshared environment. Conclusions: Despite the difficulties encountered in identifying specific sources of nonshared environment, the fact remains that most environmental variance affecting the development of psychological dimensions and psychiatric disorders is not shared by children growing up in the same family. More research and theory are needed to explain why such siblings are so different. Chance, in the sense of idiosyncratic experiences, also needs to be considered.

Nonshared Environmental Influences on Individual Differences in Early Behavioral Development: A Monozygotic Twin Differences Study

The monozygotic (MZ) twin differences method was used to investigate nonshared environmental (NSE) influences independent of genetics. Four-year-old MZ twin pairs (N = 2,353) were assessed by their parents on 2 parenting measures (harsh parental discipline and negative parental feelings) and 4 behavioral measures (anxiety, prosocial behavior, hyperactivity, and conduct problems). Within-pair differences in parenting correlated significantly with MZ differences in behavior, with an average effect size of 3%. For the extreme 10% of the parenting-discordant and behavior-discordant distributions, the average NSE effect size was substantially greater (11%), suggesting a stronger NSE relationship for more discordant twins. NSE relationships were also stronger in higher risk environments, that is, families with lower socioeconomic status, greater family chaos, or greater maternal depression.

The high heritability of educational achievement reflects many genetically influenced traits, not just intelligence

Significance Differences among children in educational achievement are highly heritable from the early school years until the end of compulsory education at age 16, when UK students are assessed nationwide with standard achievement tests [General Certificate of Secondary Education (GCSE)]. Genetic research has shown that intelligence makes a major contribution to the heritability of educational achievement. However, we show that other broad domains of behavior such as personality and psychopathology also account for genetic influence on GCSE scores beyond that predicted by intelligence. Together with intelligence, these domains account for 75% of the heritability of GCSE scores. These results underline the importance of genetics in educational achievement and its correlates. The results also support the trend in education toward personalized learning. Because educational achievement at the end of compulsory schooling represents a major tipping point in life, understanding its causes and correlates is important for individual children, their families, and society. Here we identify the general ingredients of educational achievement using a multivariate design that goes beyond intelligence to consider a wide range of predictors, such as self-efficacy, personality, and behavior problems, to assess their independent and joint contributions to educational achievement. We use a genetically sensitive design to address the question of why educational achievement is so highly heritable. We focus on the results of a United Kingdom-wide examination, the General Certificate of Secondary Education (GCSE), which is administered at the end of compulsory education at age 16. GCSE scores were obtained for 13,306 twins at age 16, whom we also assessed contemporaneously on 83 scales that were condensed to nine broad psychological domains, including intelligence, self-efficacy, personality, well-being, and behavior problems. The mean of GCSE core subjects (English, mathematics, science) is more heritable (62%) than the nine predictor domains (35–58%). Each of the domains correlates significantly with GCSE results, and these correlations are largely mediated genetically. The main finding is that, although intelligence accounts for more of the heritability of GCSE than any other single domain, the other domains collectively account for about as much GCSE heritability as intelligence. Together with intelligence, these domains account for 75% of the heritability of GCSE. We conclude that the high heritability of educational achievement reflects many genetically influenced traits, not just intelligence.

Nature and Nurture: Genetic and Environmental Influences on Behavior

The appropriate conjunction between the words nature and nurture is not versus but and. There is increasing acceptance of the evidence for substantial genetic influence on many behavioral traits, but the same research also provides the best available evidence for the importance of environmental influence and important clues about how the environment works. Because much developmental action is at the interface between genes and environment, genetic research needs to incorporate measures of the environment, and environmental research will be enhanced by collecting DNA.

X inactivation as a source of behavioural differences in monozygotic female twins

Although members of monozygotic twin pairs are identical in genome sequence, they may differ in patterns of gene expression. One early and irreversible process affecting gene expression, which can create differences within pairs of female monozygotic twins, is X inactivation - one twin can express mainly paternally-received genes on the X chromosome while the other twin expresses mainly maternally-received genes. It follows that non-identical X chromosome expression may cause female monozygotic twins to correlate less strongly than male monozygotic twins on complex behavioural traits affected by X-linked loci. We tested this hypothesis using data from around 4000 same-sex twin pairs on 9 social, behavioural and cognitive measures at ages 2, 3 and 4. Consistent with our hypothesis, monozygotic males were generally more similar than monozygotic females. Three of four significant differences were in traits showing higher correlations in males than females, and these traits - prosocial behaviour, peer problems, and verbal ability - have all been proposed previously in the literature as being influenced by genes on the X chromosome. Interestingly, dizygotic twins showed the reverse pattern of correlations for similar variables, which is also consistent with the X inactivation hypothesis; taken together, then, our monozygotic and dizygotic results suggest the presence of quantitative trait loci on the X chromosome.

Added Value Measures in Education Show Genetic as Well as Environmental Influence

Does achievement independent of ability or previous attainment provide a purer measure of the added value of school? In a study of 4000 pairs of 12-year-old twins in the UK, we measured achievement with year-long teacher assessments as well as tests. Raw achievement shows moderate heritability (about 50%) and modest shared environmental influences (25%). Unexpectedly, we show that for indices of the added value of school, genetic influences remain moderate (around 50%), and the shared (school) environment is less important (about 12%). The pervasiveness of genetic influence in how and how much children learn is compatible with an active view of learning in which children create their own educational experiences in part on the basis of their genetic propensities.

Externalizing problems in childhood and adolescence predict subsequent educational achievement but for different genetic and environmental reasons

Background Childhood behavior problems predict subsequent educational achievement; however, little research has examined the etiology of these links using a longitudinal twin design. Moreover, it is unknown whether genetic and environmental innovations provide incremental prediction for educational achievement from childhood to adolescence. Methods We examined genetic and environmental influences on parental ratings of behavior problems across childhood (age 4) and adolescence (ages 12 and 16) as predictors of educational achievement at age 16 using a longitudinal classical twin design. Results Shared‐environmental influences on anxiety, conduct problems, and peer problems at age 4 predicted educational achievement at age 16. Genetic influences on the externalizing behaviors of conduct problems and hyperactivity at age 4 predicted educational achievement at age 16. Moreover, novel genetic and (to a lesser extent) nonshared‐environmental influences acting on conduct problems and hyperactivity emerged at ages 12 and 16, adding to the genetic prediction from age 4. Conclusions These findings demonstrate that genetic and shared‐environmental factors underpinning behavior problems in early childhood predict educational achievement in midadolescence. These findings are consistent with the notion that early‐childhood behavior problems reflect the initiation of a life‐course persistent trajectory with concomitant implications for social attainment. However, we also find evidence that genetic and nonshared‐environment innovations acting on behavior problems have implications for subsequent educational achievement, consistent with recent work arguing that adolescence represents a sensitive period for socioaffective development.

Differences in exam performance between pupils attending selective and non-selective schools mirror the genetic differences between them

On average, students attending selective schools outperform their non-selective counterparts in national exams. These differences are often attributed to value added by the school, as well as factors schools use to select pupils, including ability, achievement and, in cases where schools charge tuition fees or are located in affluent areas, socioeconomic status. However, the possible role of DNA differences between students of different schools types has not yet been considered. We used a UK-representative sample of 4814 genotyped students to investigate exam performance at age 16 and genetic differences between students in three school types: state-funded, non-selective schools (‘non-selective’), state-funded, selective schools (‘grammar’) and private schools, which are selective (‘private’). We created a genome-wide polygenic score (GPS) derived from a genome-wide association study of years of education (EduYears). We found substantial mean genetic differences between students of different school types: students in non-selective schools had lower EduYears GPS compared to those in grammar (d = 0.41) and private schools (d = 0.37). Three times as many students in the top EduYears GPS decile went to a selective school compared to the bottom decile. These results were mirrored in the exam differences between school types. However, once we controlled for factors involved in pupil selection, there were no significant genetic differences between school types, and the variance in exam scores at age 16 explained by school type dropped from 7% to <1%. These results show that genetic and exam differences between school types are primarily due to the heritable characteristics involved in pupil admission.Genetic differences between selective and non-selective schoolsStudents attending selective schools have, on average, more genetic variants associated with educational attainment compared to students attending non-selective schools. A team led by Professor Robert Plomin at King’s College London found that these genetic differences between school types were also mirrored in examination differences. Students attending selective schools were performing a grade higher than their non-selective schooled peers. However, once the researchers statistically accounted for student-level factors, including family socioeconomic status, prior ability and prior achievement, there were no significant genetic differences between students in selective and non-selective schools, and only small examination score differences. This research shows that genetic and exam score differences between selective and non-selective schools are primarily due to the genetically influenced characteristics involved in student admission.

National differences in mindset among students who plan to be teachers

A growth mindset has been found beneficial to students, particularly when they encounter academic setbacks (Dweck, 2000). Evidence suggests that teachers’ own mindsets may influence those of their students. We assessed mindset among student teachers from different places of origin (UK and East Asia) in a UK university (N = 255). Although both groups were relatively growth-minded, those brought up in the UK were significantly more so than those brought up in East Asia (F(4, 228) = 26.52, p < .001, Wilks λ = .68, = .32). Furthermore, UK student teachers reported higher levels of growth mindset than East Asian student teachers in relation to pupils’ academic potential, behavior, dyslexia, and ADHD. Implications for education are discussed.

Nature and Nurture in the Family

SUMMARY Behavioral genetic research provides the best evidence we have for the importance of the environment. Heritabilities rarely exceed 50%, which means that, on average, half of the variance for behavioral dimensions and disorders is not genetic in origin. However, no one needed to be convinced that environmental factors contribute importantly to behavior. The two findings that stand out as the most important from behavioral genetics both involve nurture rather than nature. This volume reviews these findings and lays out the agenda for future research in this area. Some of the ideas described in these papers may be unfamiliar to marriage and family researchers, in part because they are so novel and revolutionary. Nonetheless this volume will reward careful reading as it represents an exciting glimpse of the future of research in this area.