Human behavior genetics

Genetic and Environmental In‘uences on Personality in Adult Russian Twins

The present study explored genetic and environmental contributions to personality in a sample of twins participating in the Adult Russian Twin Study (ARTS). Subjects included 79 monozygotic (MZ) and 51 dizygotic (DZ) twin-pairs residing in the metropolitan Moscow area, Russia (mean age 42.2 years). Twins completed self-report questionnaires assessing the personality dimensions of neuroticism, extraversion, monotony avoidance, and impulsivity. For all four dimensions, model-”tting analyses yielded estimates of heritability consistent with previous behavioural genetic findings ( h2 ranging from .49 to .59). Also consistent with previous research is the finding that shared environmental variance is negligible for each dimension. These results suggest that the factors that influence individual differences in personality in the Russian culture do not substantially differ from those that influence personality in more Western cultures.

Genetic and environmental contributions to individual differences: the three major dimensions of personality

This article deals with the contribution of genetic and environmental factors to individual differences in the three major dimensions of personality (Psychoticism, Extraversion, and Neuroticism). Twin studies indicate, and family studies confirm within limits, the strong genetic determination of these and many other personality factors, additive genetic variance accounting for roughly half the total phenotypic variance. On the environmental side, shared family environment plays little or no part, all environmental effects being within-family. Assortative mating, important in the formation of social attitudes, has little impact on personality. Dominance may be important for Extraversion. Epistasis (emergenesis) may account for the comparative low values of dizygotic (DZ) twins' correlations. Evidence for differential heritability of traits is present, but not very strong. It is concluded that behavioral genetics forms a vital part of the psychological understanding of the causes of individual differences in personality.

Is adolescent bullying an evolutionary adaptation?

Bullying appears to be ubiquitous across cultures, involving hundreds of millions of adolescents worldwide, and has potentially serious negative consequences for its participants (particularly victims). We challenge the traditionally held belief that bullying results from maladaptive development by reviewing evidence that bullying may be, in part, an evolved, facultative, adaptive strategy that offers some benefits to its practitioners. In support of this view, we draw from research that suggests bullying serves to promote adolescent bullies' evolutionarily-relevant somatic, sexual, and dominance goals, has a genetic basis, and is widespread among nonhuman animals. We identify and explain differences in the bullying behavior of the two sexes, as well as when and why bullying is adaptive and when it may not be. We offer commentary on both the failures and successes of current anti-bullying interventions from an evolutionary perspective and suggest future directions for both research and anti-bullying interventions.

Happy families: a twin study of humour

The objective of this study was to estimate how much of an individual's appreciation of humour is influenced by genetic factors, the shared environment or the individual's unique environment. A population-based classical twin study of 127 pairs of female twins (71 monozygous (MZ) and 56 dizygous (DZ) pairs) aged 20–75 from the St Thomas' UK Adult Twin Registry elicited responses to five ‘Far Side’ Larson cartoons on a scale of 0–10. Within both MZ and DZ twin pairs, the tetrachoric correlations of responses to all five cartoons were significantly greater than zero. Furthermore, the correlations for MZ and DZ twins were of similar magnitude and in some cases the DZ correlation was greater than that of the MZ twins. This pattern of correlations suggests that shared environment rather then genetic effects contributes to cartoon appreciation. Multivariate model-fitting confirmed that these data were best explained by a model that allowed for the contribution of the shared environment and random environmental factors, but not genetic effects. However, there did not appear to be a general humour factor underlying responses to all five cartoons and no effect of age was seen. The shared environment, rather than genetic factors, explains the familial aggregation of humour appreciation as assessed by the specific ‘off the wall’ cognitive type of cartoons used in this study. Twin Research (2000) 3, 17–22.

Adolescent religiousness and its influence on substance use: preliminary findings from the Mid-Atlantic School Age Twin Study

Research has consistently shown that religiousness is associated with lower levels of alcohol and drug use, but little is known about the nature of adolescent religiousness or the mechanisms through which it influences problem behavior in this age group. This paper presents preliminary results from the Mid-Atlantic School Age Twin Study, a prospective, population-based study of 6–18-year-old twins and their mothers. Factor analysis of a scale developed to characterize adolescent religiousness, the Religious Attitudes and Practices Inventory (RAPI), revealed three factors: theism, religious/spiritual practices, and peer religiousness. Twin correlations and univariate behavior-genetic models for these factors and a measure of belief that drug use is sinful reveal in 357 twin pairs that common environmental factors significantly influence these traits, but a minor influence of genetic factors could not be discounted. Correlations between the multiple factors of adolescent religiousness and substance use, comorbid problem behavior, mood disorders, and selected risk factors for substance involvement are also presented. Structural equation modeling illustrates that specific religious beliefs about the sinfulness of drugs and level of peer religiousness mediate the relationship between theistic beliefs and religious/spiritual practices on substance use. Limitations and future analyses are discussed.

Insensitivity of the analysis of variance to heredity-environment interaction

It makes sense to attribute a definite percentage of variation in some measure of behavior to variation in heredity only if the effects of heredity and environment are truly additive. Additivity is often tested by examining the interaction effect in a two-way analysis of variance (ANOVA) or its equivalent multiple regression model. If this effect is not statistically significant at the α = 0.05 level, it is common practice in certain fields (e.g., human behavior genetics) to conclude that the two factors really are additive and then to use linear models, which assume additivity. Comparing several simple models of nonadditive, interactive relationships between heredity and environment, however, reveals that ANOVA often fails to detect nonadditivity because it has much less power in tests of interaction than in tests of main effects. Likewise, the sample sizes needed to detect real interactions are substantially greater than those needed to detect main effects. Data transformations that reduce interaction effects also change drastically the properties ofthe causal model and may conceal theoretically interesting and practically useful relationships. If the goal ofpartitioning variance among mutually exclusive causes and calculating “heritability” coefficients is abandoned, interactive relationships can be examined more seriously and can enhance our understanding of the ways living things develop.

The nature of nurture: Genetic influence on “environmental” measures

Evidence for genetic influence on environmental measures will emerge in quantitative genetic analyses if genetically influenced characteristics of individuals are assessed by these environmental measures. Recent twin and adoption studies indicate substantial genetic influence when measures of the environment are treated as phenotypes in genetic analyses. Genetic influence has been documented for measures as diverse as videotaped observations of parental behavior toward their children, ratings by parents and children of their family environment, and ratings of peer groups, social support, and life events. Evidence for genetic influence on environmental measures includes some of the most widely used measures of environment – the Home Observation for Measurement of the Environment, the Family Environment Scales, and the Social Readjustment Rating Scale of life events, for example. The goal of this article is to document and discuss these findings and to elicit commentary that might help to shape the course of research on this topic, which has far-reaching implications for the behavioral and brain sciences.

Why are children in the same family so different from one another?

One of the most important findings that has emerged from human behavioral genetics involves the environment rather than heredity, providing the best available evidence for the importance of environmental influences on personality, psychopathology, and cognition. The research also converges on the remarkable conclusion that these environmental influences make two children in the same family as different from one another as are pairs of children selected randomly from the population.

The theme of the target article is that environmental differences between children in the same family (called “nonshared environment”) represent the major source of environmental variance for personality, psychopathology, and cognitive abilities. One example of the evidence that supports this conclusion involves correlations for pairs of adopted children reared in the same family from early in life. Because these children share family environment but not heredity, their correlation directly estimates the importance of shared family environment. For most psychological characteristics, correlations for adoptive “siblings” hover near zero, which implies that the relevant environmental influences are not shared by children in the same family. Although it has been thought that cognitive abilities represent an exception to this rule, recent data suggest that environmental variance that affects IQ is also of the nonshared variety after adolescence.

The article has three goals: (1) To describe quantitative genetic methods and research that lead to the conclusion that nonshared environment is responsible for most environmental variation relevant to psychological development, (2) to discuss specific nonshared environmental influences that have been studied to date, and (3) to consider relationships between nonshared environmental influences and behavioral differences between children in the same family. The reason for presenting this article in BBS is to draw attention to the far-reaching implications of finding that psychologically relevant environmental influences make children in a family different from, not similar to, one another.

Social versus reproductive success: The central theoretical problem of human sociobiology

The fundamental postulate of sociobiology is that individuals exploit favorable environments to increase their genetic representation in the next generation. The data on fertility differentials among contemporary humans are not cotvietent with this postulate. Given the importance ofHomo sapiensas an animal species in the natural world today, these data constitute particularly challenging and interesting problem for both human sociobiology and sociobiology as a whole.

The first part of this paper reviews the evidence showing an inverse relationship between reproductive fitness and “endowment” (i.e. wealth, success, and measured aptitudes) in contemporary, urbanized societies. It is shown that a positive relationship is observed only for those cohorts who bore their children during a unique period of rising fertility, 1935–1960, and that these cohorts are most often cited by sociobiologists as supporting the central postulate of sociobiology. Cohorts preceding and following these show the characteristic inverse relationship between endowment and fertility. The second section reviews the existing so-ciobiological models of this inverse relationship, namely, those of Barkow, Burley, and Irons, as well as more informal responses among sociobiologists to the persistent violation of sociobiology's central postulate, such as those of Alexander and Dawkins. The third section asks whether the goals of sociobiology, given the violation of its fundamental postulate by contemporary human societies, might not be better thought of as applied rather than descriptive, with respect to these societies. A proper answer to this question begins with the measurement of the pace and direction of natural selection within modern human populations, as compared to other sources of change. The vast preponderance of the shifts in human trait distributions, including the IQ distribution, appears to be due to environmental rather than genetic change. However, there remains the question of just how elastic these distributions are in the absence of reinforcing genetic change.