Heritability of personality in children

On the Nature and Nurture of Intelligence and Specific Cognitive Abilities

To further knowledge concerning the nature and nurture of intelligence, we scrutinized how heritability coefficients vary across specific cognitive abilities both theoretically and empirically. Data from 23 twin studies (combined N = 7,852) showed that (a) in adult samples, culture-loaded subtests tend to demonstrate greater heritability coefficients than do culture-reduced subtests; and (b) in samples of both adults and children, a subtest’s proportion of variance shared with general intelligence is a function of its cultural load. These findings require an explanation because they do not follow from mainstream theories of intelligence. The findings are consistent with our hypothesis that heritability coefficients differ across cognitive abilities as a result of differences in the contribution of genotype-environment covariance. The counterintuitive finding that the most heritable abilities are the most culture-dependent abilities sheds a new light on the long-standing nature-nurture debate of intelligence.

Social-emotional development through a behavior genetics lens: infancy through preschool

The field of developmental behavior genetics has added significantly to the collective understanding of what factors influence human behavior and human development. Research in this area has helped to explain not only how genes and environment contribute to individual differences but also how the interplay between genes and environment influences behavior and human development. The current chapter provides a background of the theory and methodology behind behavior genetic research and the field of developmental behavior genetics. It also examines three specific developmental periods as they relate to behavior genetic research: infancy, toddlerhood, and early preschool. The behavior genetic literature is reviewed for key socioemotional developmental behaviors that fit under each of these time periods. Temperament, attachment, frustration, empathy, and aggression are behaviors that develop in early life that were examined here. Thus, the general purpose of this chapter is to provide an overview of how genes and environment, as well as the interplay between them, relate to early socioemotional behaviors.

Human aggression across the lifespan: genetic propensities and environmental moderators

This chapter reviews the recent evidence of genetic and environmental influences on human aggression. Findings from a large selection of the twin and adoption studies that have investigated the genetic and environmental architecture of aggressive behavior are summarized. These studies together show that about half (50%) of the variance in aggressive behavior is explained by genetic influences in both males and females, with the remaining 50% of the variance being explained by environmental factors not shared by family members. Form of aggression (reactive, proactive, direct/physical, indirect/relational), method of assessment (laboratory observation, self-report, ratings by parents and teachers), and age of the subjects-all seem to be significant moderators of the magnitude of genetic and environmental influences on aggressive behavior. Neither study design (twin vs. sibling adoption design) nor sex (male vs. female) seems to impact the magnitude of the genetic and environmental influences on aggression. There is also some evidence of gene-environment interaction (G × E) from both twin/adoption studies and molecular genetic studies. Various measures of family adversity and social disadvantage have been found to moderate genetic influences on aggressive behavior. Findings from these G × E studies suggest that not all individuals will be affected to the same degree by experiences and exposures, and that genetic predispositions may have different effects depending on the environment.

Individual differences in multiple dimensions of aggression: a univariate and multivariate genetic analysis

Previous behaviour genetic studies of aggression have yielded inconsistent results: reported heritabilities for different types of aggressive behaviour ranging from 0 to 0.98. In the present study, 247 adult twin pairs (183 MZ pairs; 64 same-sex DZ pairs) were administered seven self-report questionnaires which yielded 18 measures of aggression. Univariate genetic analyses showed moderate to high heritabilities for 14 of these 18 measures and for a general aggression factor and three correlated aggression factors extracted from the measures. Multivariate genetic analyses showed sizeable genetic correlations between the different dimensions of aggression. Thus, individual differences in many types of aggressive behaviour are attributable to some extent to genetic factors and there is considerable overlap between the genes that operate on different types of aggressive behaviour.

Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies

A meta-analysis of twin, family and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on impulsivity. The best fitting model for 41 key studies (58 independent samples from 14 month old infants to adults; N=27,147) included equal proportions of variance due to genetic (0.50) and non-shared environmental (0.50) influences, with genetic effects being both additive (0.38) and non-additive (0.12). Shared environmental effects were unimportant in explaining individual differences in impulsivity. Age, sex, and study design (twin vs. adoption) were all significant moderators of the magnitude of genetic and environmental influences on impulsivity. The relative contribution of genetic effects (broad sense heritability) and unique environmental effects were also found to be important throughout development from childhood to adulthood. Total genetic effects were found to be important for all ages, but appeared to be strongest in children. Analyses also demonstrated that genetic effects appeared to be stronger in males than in females. Method of assessment (laboratory tasks vs. questionnaires), however, was not a significant moderator of the genetic and environmental influences on impulsivity. These results provide a structured synthesis of existing behavior genetic studies on impulsivity by providing a clearer understanding of the relative genetic and environmental contributions in impulsive traits through various stages of development.

You can get here from there

During one of the several unsuccessful admission interviews I had before finally being admitted to a graduate program, an interviewer asked me what kind of research I would like to do as a psychologist. "I plan to validate the Rorschach" was my reply. "And what will you do if you find the Rorschach isn't valid?" was the interviewer's next question. I don't recall my answer but it was obviously inadequate because such an unlikely possibility hadn't occurred to me, and I wasn't admitted to that program. Looking back, it is very clear how one thing led to another so that instead of validating the Rorschach, I ended up exploring the contribution of genetic factors to stress ulcers in rats and children's personality.

Heritability of irritable impulsiveness: a study of twins reared together and apart

The heritability of self-reported personality traits related to impulsiveness, irritability, and the inhibition of assertive or aggressive behavior was examined in up to 500 healthy monozygotic and dizygotic twin pairs raised together or apart. Two factors related to "(lack of) assertiveness/aggression" (Factor I) and "impulsive irritability" (Factor II) were examined using traditional and model-fitting procedures. Results of model-fitting procedures were consistent with a genetic, but not a shared environmental, influence for both factors. Further analysis suggested a nonadditive genetic influence for Factor II and an additive influence for Factor I. Bivariate model-fitting analyses suggest that self-reported "irritable impulsiveness" and "(lack of) assertiveness/aggressiveness" show substantial, though different, genetic influences.

Genetic correlates and sex differences in Holtzman Inkblot Technique responses of twins

Holtzman Inkblot Technique (HIT) responses of 36 monozygotic (MZ), 18 dizygotic same-sex (DZ-S) and 29 dizygotic opposite-sex (DZ-O) college student twin pairs were analyzed. MZ group twins were significantly more alike across a variety of HIT response dimensions than DZ-S or DZ-O group twins. The following variables indicated a possible significant genetic contribution to response determination: Movement, Abstract Content, Hostility, Pathognomic Verbalization and Popular Responses. DZ-O groups data (representing a high degree of control for environmental influences) indicated significant sex differences on the following variables: M less than F -- Rejection, Form Appropriateness, Anatomical Content, and Balance; F less than M -- Human Content and Popular. The results are discussed in terms of (a) comparable genetic determination studies with Rorschach responses and (b) the necessity for separate male and female norms on several HIT scored response scales.

Blood type gene frequency and mental ability: premature conclusions?

2 attempts to replicate suspected relationships among blood groups and mental ability using multiple regression failed. The problem of statistical inference in stepwise multiple regression is discussed and illustrated with a Monte Carlo example.