Turner syndrome: a review of genetic and hormonal influences on neuropsychological functioning.

Turner syndrome (TS) is a genetic disorder affecting mainly females that arises from a loss of X chromosome material, most usually one of the two X chromosomes. TS is associated with a number of characteristic physical features such as short stature and absent ovaries as well as a set of common neuropsychological deficits and social and behavioral features. This paper will serve to review the cognitive, social, and psychoeducational abilities of individuals with TS as well as neuroimaging findings. Several putative genetic mechanisms contributing to their particular neurocognitive deficits will also be described including candidate genes. In addition, the available evidence on how hormones affect specific abilities in TS will be reviewed. It will be concluded that the TS neurobehavioral profile arises from an atypical cerebral organization caused by the complex interplay of insufficient expression of certain (unknown) genes on the X chromosome and by abnormal hormonal levels; however, it is still not clear exactly how the specific genes affect broader cognitive abilities. Future research needs to identify the elemental processes that are disturbed in TS and map these both to events in early brain development and subsequent brain function and to specific gene and hormonal contributions.     

Evolution and the hormonal control of sexually-dimorphic spatial abilities in humans

A number of hypotheses have been proposed for the evolution of sex differences in spatial ability. Two of these hypotheses assume a sex-based division of labor in foraging during human evolutionary history, three propose sexual selection for spatial ability, and two suggest that human life history has imposed sex-specific selection on spatial abilities. We derive predictions from each of these models and test the predictions against recent data on the effects of hormones on spatial ability across the lifespan. Sexual selection for increased range size in males might be the evolutionary origin of the enhancing effects of testosterone on spatial ability, while the benefits of reduced mobility in women at different stages of reproduction could be the origin of the inhibitory effects of oestrogen on spatial ability.     

Predicting environmental learning from spatial abilities: An indirect route

Relationships among spatial abilities, as assessed by a battery of psychometric tests and experimental tasks, and environmental learning, as assessed by a series of macrospatial tasks, were examined in two studies using confirmatory factor analysis with directional paths. The initial study indicated the utility of a five-factor model, one (general spatial ability) derived from psychometric tests, two (spatial-sequential memory and spatial perspective-taking latency) from experimental tasks, and two (topological knowledge and Euclidean direction knowledge) from measures of environmental learning. The best fitting path model further indicated that the spatial-sequential memory factor mediated the relationship between general spatial ability and topological knowledge, and that perspective-taking latency mediated the relationship between general spatial ability and Euclidean direction knowledge. The second study confirmed the five-factor path model using a different participant sample and environmental setting. The only failure to replicate involved the path between perspective-taking latency in the lab and Euclidean direction knowledge in the environment. Results indicate that the relationship between basic spatial abilities and environmental learning is significantly mediated by cognitive processes that can be assessed using laboratory tasks.     

Herrnstein''s syllogism: genetic and shared environmental influences on IQ, education, and income

Genotypes may influence the phenotypic associations among IQ, education, and income. To investigate this hypothesis, we believe that the appropriate methodology requires estimation of genetic and environmental influences using data able to separate these influences. The National Longitudinal Survey of Youth (NLSY) is a nationally representative sample that contains genetically-informative full- and half-siblings (28–35 years old in 1992; Ns=1943 full-siblings, 129 half-siblings). A biometric genetic model was fit that estimated the shared environmental and genetic variance components of IQ, years of education, and hourly income. The total heritabilities were 0.64 for IQ, 0.68 for education, and 0.42 for income. Heritabilities due to a common genetic factor were 0.35 for IQ, 0.52 for education, and 0.12 for income. Environmental influences due to a common shared environmental factor were 0.23 for IQ, 0.18 for education, and 0.08 for income. The model predicted a correlation of 0.63 between IQ and education and 0.34 between IQ and income. Sixty-eight percent of the former and 59% of the latter was genetically mediated; the remainder was mediated by common shared environment. These findings suggest that social inequality in the United States has its origin in both genetically-based traits and in different environmental backgrounds.     

The structure of genetic influences on general cognitive, language, phonological, and reading abilities

The etiology of individual differences in literacy, phonological awareness, and language ability is reported in 126 pairs of monozygotic and dizygotic twins. At age 6 and 7 years, more than 60% of the variance in literacy was heritable. Heritabilities for 6- and 7-year-olds were .52 and .62, respectively, for phonological awareness and .43 and .50, respectively, for language ability. After genetic effects on IQ were controlled, a separate genetic influence was identified that acted on literacy, phonological awareness, and language. No genetic link between phonological awareness and literacy independent of general language ability was found; such covariance was mediated through environmental influences. Individual differences in literacy ability are substantially influenced by genetic factors, some of which also act on phonological awareness and general language ability.     

The nature of environmental influences on weight and obesity: a behavior genetic analysis.

The nature of environmental influences on individual differences in weight and obesity is presently unclear. To resolve this issue, behavior genetic studies are reviewed for their relevance to environmental influences on weight and obesity. Results are consistent in suggesting that environmental experiences are important for weight and obesity, although they account for much less variation than do the effects of genes. Furthermore, only environmental experiences that are not shared among family members appear to be important. In contrast, experiences that are shared among family members appear largely irrelevant in determining individual differences in weight and obesity. These conclusions are consistent with a growing body of evidence on the relative unimportance of such shared experiences for many psychological characteristics.     

Sources of structure: genetic, environmental, and artifactual influences on the covariation of personality traits

The phenotypic structure of personality traits has been well described, but it has not yet been explained causally. Behavior genetic covariance analyses can identify the underlying causes of phenotypic structure; previous behavior genetic research has suggested that the effects from both genetic and nonshared environmental influences mirror the phenotype. However, nonshared environmental effects are usually estimated as a residualterm that may also include systematic bias, such as that introduced by implicit personality theory. To reduce that bias, we supplemented data from Canadian and German twin studies with cross-observer correlations on the Revised NEO Personality Inventory. The hypothesized five-factor structure was found in both the phenotypic and genetic/familial covariances. When the residual covariance was decomposed into true nonshared environmental influences and method bias, only the latter showed the five-factor structure. True nonshared environmental influences are not structured as genetic influences are, although there was some suggestion that they do affect two personality dimensions, Conscientiousness and Love. These data reaffirm the value of behavior genetic analyses for research on the underlying causes of personality traits.     

The intelligence of the Mongoloids: A psychometric, evolutionary and neurological theory

This paper presents a theory of the intelligence of the Mongoloids consisting of three linked sub-theories. The first concerns the psychometric features of Mongoloid intelligence and proposes that Mongoloids are characterised by high general intelligence (Spearman's g), high visuospatial abilities and low verbal abilities. Mongoloid abilities also display slow maturation in infancy and early childhood. It is proposed that this pattern of abilities cannot be explained in environmental terms and should be regarded as substantially genetically programmed. The second sub-theory presents an evolutionary explanation for this pattern of abilities in Mongoloids, whereby it is proposed that the extreme cold of the ice ages acted as a selection pressure for increases in Spearman's g and the visuospatial abilities. The low verbal abilities and slow maturation rates are interpreted as by-products of these adaptations. The third sub-theory presents a neurological model for the Mongoloid brain in which it is proposed that cortex devoted to the visuospatial abilities was expanded at the expense of the cortex devoted to the verbal abilities. The implication that there exists a negative correlation between the visuospatial abilities and the verbal abilities is considered in the concluding part of the paper and shown to be correct.     

Global influences on the development of spatial and object perceptual categorization abilities: Evidence from preterm infants

Influences on the development of perceptual categorization were examined by comparing the performance of three groups of infants on spatial and object categorization tasks. The groups consisted of 1) fullterm infants tested at 3 to 4 months of age, 2) healthy preterm infants tested 3 to 4 months from birth (postnatals), and 3) healthy preterm infants tested 3 to 4 months from their due date (postterms). Four experiments showed that fullterms and postterms outperformed postnatals on a spatial categorization task (i.e., ‘above’ vs. ‘below’, and that fullterms outperformed both postnatals and postterms on object categorization tasks (i.e., dogs vs. cats, and cats vs. birds). These results suggest that maturation may be the predominant influence on the early development of the ability to form categorical representations of spatial information, while preterm birth may exert a limiting influence on the development of object categorization abilities.     

Correlation between inspection time and psychometric abilities: A personal interpretation

More than 25 years of research suggests that the measure inspection time (IT) does capture low-level aspects of cognitive functioning that contribute to human intelligence. However, recent evidence does not support earlier claims that IT estimates the speed of a single mechanism like “sampling input” or “apprehension.” Rather, together with other tasks that employ pattern backward masking to limit the duration for which information is available for processing, IT is probably sensitive both to focused attentional capacities to detect organization and change under severe time constraints and to decision processes, ongoing beyond mask onset, that monitor responding. Among normal young adults, IT is correlated with the broad psychometric factor Gs (“speediness”). This mediates correlation with general intelligence. In this group, IT is not correlated with Gf. However, whether this outcome generalizes to samples of persons with an intellectual disability, to young children, or to elderly persons is not yet known. Psychological processes underpinning IT are currently only speculatively defined, but it should prove possible to unravel these by experimentation. To this end, backward masking procedures are arguably more theoretically tractable than reaction time tasks because they reduce the impact of higher-level cognitive strategies on performance. On this basis, IT may hold promise as a means for developing partial explanations for intelligence in psychological terms. However, whether this is realized depends on identifying the psychological functions that support IT.     

Human genetic markers associated with variation in intellectual abilities and personality

Eight commonly-used genetic markers were correlated with the Verbal Reasoning (VR), Space Relations (SR) and Clerical Speed and Accuracy (CSA) tests of the Differential Aptitude Tests (DAT) and the Psychoticism (P), Extraversion (E), Neuroticism (N) and Lie (L), scales of the Eysenck Personality Questionnaire (EPQ). In a sample of 122 undergraduate students tongue-curling ability, light eye color and inability to taste PTC were related to high intelligence, with dominant right eye, disconnected ear lobes and near-sightedness being associated with specific DAT scales. P showed a male-female sex difference. Dark eyes were related to E and N.     

Adolescent personality moderates genetic and environmental influences on relationships with parents

In contrast with early theories of socialization that emphasized the role of parents in shaping their children's personalities, recent empirical evidence suggests an evocative relationship between adolescent personality traits and the quality of the parent-adolescent relationship. Research using behavior genetic methods suggests that the association between personality and parenting is genetically mediated, such that the genetic effects on adolescent personality traits overlap with the genetic effects on parenting behavior. In the current study, the authors examined whether the etiology of this relationship might change depending on the adolescent's personality. Biometrical moderation models were used to test for gene- environment interaction and correlation between personality traits and measures of conflict, regard, and involvement with parents in a sample of 2,452 adolescents (M age = 17.79 years). They found significant moderation of both positive and negative qualities of the parent-adolescent relationship, such that the genetic and environmental variance in relationship quality varied as functions of the adolescent's levels of personality. These findings support the importance of adolescent personality in the development of the quality of the parent-adolescent relationship.     

Personality related traits as predictors of music practice: Underlying environmental and genetic influences

Little is known about reasons for individual differences in practice behavior – why do some individuals practice more than others? Here we explore personality related traits such as openness, motivation and flow proneness as well as IQ as potential predictors of music practice. Using a large Swedish twin cohort of more than 10,500 individuals we also estimated genetic and environmental influences underlying such associations. Significant associations with music practice were found for IQ, intrinsic motivation, music flow, and openness. With all predictors in the same model (including sex and age) we could explain about 25% of variance in music practice. However, IQ and intrinsic motivation became non-significant in the full model, with music specific flow being the strongest predictor of music practice. Multivariate genetic modeling with the two remaining significant predictors (openness and music flow) and music practice suggested that the associations between the variables were largely due to shared genetic influences with some additional non-shared environmental influences. Our findings suggest that common genes may influence both music practicing behavior and traits related to artistic interests and musical enjoyment (flow).     

Women who excel on a spatial task: proposed genetic and environmental factors

A "bent twig" model which incorporates Annett's genetic handedness theory with an environmental component predicted characteristics of college women likely to excel on a mental rotation task. Those likely to have the necessary combination of genetic potential and prior experiences are right-handed women with non-right-handed relatives who rate themselves high in spatial experiences. This subgroup significantly outperformed all other groups of right-handed women on the Vandenberg Mental Rotation Test. This study provides support for the view that family handedness and spatial experiences are important factors influencing mental rotation ability in women.     

Girls who use masculine problem-solving strategies on a spatial task: proposed genetic and environmental factors.

This study investigated strategy and performance differences between right-handed boys and girls on a mental rotation task. Based on predictions from Casey and Brabeck's (1990) theory of sex differences, the study was also designed to identify a target group of right-handed girls with the optimal combination of genetic and environmental factors (high math/science achievers with nonright-handed immediate relatives). They were predicted to show strategies and performance more similar to those of the boys than to those of both the low math/science achieving girls and the high math/science girls with all right-handed immediate relatives (predicted to have the nonoptimal genotype). Strategy preference was measured using selective interference, whereby subjects solved mental rotation items concurrently with either verbal or visual-spatial interference tasks. Group comparisons were made on the amount of decrement in mental rotation performance as a result of the two types of interference tasks. This provided a basis for comparing the groups on the use of visual-spatial or verbal strategies on the mental rotation task. The boys: (1) did not show a significant advantage over the girls on the mental rotation items, but (2) did depend more on visual-spatial strategies than the girls, and (3) depended less on verbal strategies than the girls. The target girls: (1) outperformed the low math/science achieving girls on the mental rotation items and did not show a significant advantage over the other high math/science group, (2) depended more on visual-spatial strategies than both the other two groups of girls, and (3) depended less on verbal strategies than the low math/science girls, while showing no significant difference compared to the nonoptimal high math/science girls. Examining within-group differences, the boys preferred visual-spatial strategies, while the girls in both the nontarget groups preferred verbal ones. However, for the target girls, no within-subject strategy differences were found. The present findings support the theory that, like the boys, the target girls depend more on visual-spatial strategies than do other girls. It is possible that the target girls use a combination of visual-spatial and verbal strategies when solving mental rotation tasks.     

Prosocial behavior from early to middle childhood: genetic and environmental influences on stability and change

Prosocial behavior is important for the functioning of society. This study investigates the extent to which environment shared by family members, nonshared environment, and genetics account for children's prosocial behavior. The prosocial behavior of twins (9,424 pairs) was rated by their parents at the ages of 2, 3, 4, and 7 and by their teachers at age 7. For parent ratings, shared environmental effects decreased from .47 on average at age 2 to .03 at age 7, and genetic effects increased from .32 on average to .61. The finding of weak shared environmental effects and large heritability at age 7 was largely confirmed through the use of teacher ratings. Using longitudinal genetic analyses, the authors conclude that genetic effects account for both change and continuity in prosocial behavior and nonshared environment contributes mainly to change.     

Genetic and environmental influences on antisocial behavior: a meta-analysis of twin and adoption studies

A meta-analysis of 51 twin and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on antisocial behavior. The best fitting model included moderate proportions of variance due to additive genetic influences (.32), nonadditive genetic influences (.09), shared environmental influences (.16), and nonshared environmental influences (.43). The magnitude of familial influences (i.e., both genetic and shared environmental influences) was lower in parent-offspring adoption studies than in both twin studies and sibling adoption studies. Operationalization, assessment method, zygosity determination method, and age were significant moderators of the magnitude of genetic and environmental influences on antisocial behavior, but there were no significant differences in the magnitude of genetic and environmental influences for males and females.     

Sex differences in genetic and environmental influences on DSM-III-R attention-deficit/hyperactivity disorder

Approximately 5% of children are affected by attention-deficit/hyperactivity disorder (ADHD), and more boys are affected than girls. This study examined the magnitude of genetic and environmental influences on ADHD and several questions regarding sex differences in its prevalence and liability. The participants were 2,391 twin and sibling pairs from Australia, ages 3-18. ADHD symptoms in the general population were highly heritable (h2 = .85-.90), as were deviant ADHD scores in the selected population. The magnitude of familial influences was similar for boys and girls, although there were shared environmental influences on ADHD in girls but not boys and dominance genetic influences on ADHD in boys but not girls. Specific genetic and environmental influences were highly similar for boys and girls. Evidence supported the polygenic multiple threshold model rather than the constitutional variability model of sex differences in ADHD.