Exploring the genetic and environmental etiology of high general cognitive ability in fourteen- to thirty-six-month-old twins

Two definitions of normality ("isolated" or "correlated") are considered. The boundaries of "isolated" normality were determined by a statistical procedure, whereas the "correlated" approach was related to a clinical or predictive definition. In the latter case, the biological variations were considered abnormal if they implied a hazard with some significant future ailment as a risk factor. In this pragmatic approach, the upper limit of normal/abnormal variations is the point beyond which medical strategy is related to the most expected benefit when applied to a definite population or to an individual patient. The capacity of a diagnostic test to discriminate between patients with a defined risk and those without risk depends strictly on the value of the parameter chosen. In medical care for the prevention of vascular complications in diabetic patients or with foetal risks in pregnant women, the limits of the so-called normal range of glycaemia and other parameters should be determined according to the objective of the preventive and/or therapeutic measures to be prescribed.     

Intelligence: Genetics, Genes, and Genomics.

More is known about the genetics of intelligence than about any other trait, behavioral or biological, which is selectively reviewed in this article. Two of the most interesting genetic findings are that heritability of intelligence increases throughout the life span and that the same genes affect diverse cognitive abilities. The most exciting direction for genetic research on intelligence is to harness the power of the Human Genome Project to identify some of the specific genes responsible for the heritability of intelligence. The next research direction will be functional genomics--for example, understanding the brain pathways between genes and intelligence. Deoxyribonucleic acid (DNA) will integrate life sciences research on intelligence; bottom-up molecular biological research will meet top-down psychological research in the brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic differences between humans and chimps and among humans.

Challenges S. L. Washburn's (see record 1979-12215-001) assertion that humans and chimpanzees share 99% of their genetic material and that humans, therefore, share more than 99% of their genes. Evidence is presented for inter- and intraspecial behavioral differences that are genetically influenced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic influence on life events during the last half of the life span.

Genetic influence of perceptions of major events later in life was assessed with a combination of twin and adoption designs as part of the Swedish Adoption/Twin Study of Aging (SATSA). The SATSA design includes 4 groups totaling 399 pairs of same-sex twins: identical and fraternal twins reared apart and matched twins reared together. The average age of the twins was 59 years. The results demonstrate significant genetic influence on reports of the occurrences of life events, especially for controllable events in which the individual can play an active role. Maximum likelihood model-fitting estimates of genetic influence indicate that 40% of the variance of the total life events score is due to genetic differences among individuals. How genetic factors can affect life experiences and directions for future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Co-occurrence of depressive symptoms and antisocial behavior in adolescence: A common genetic liability.

Recent reviews of research on child and adolescent psychopathology have highlighted the consistently high rates of co-occurring dimensions of psychopathology, particularly between internalizing and externalizing disorders, and have suggested that further research examining the causes of co-occurring syndromes is needed. The authors examined this question in a national sample of 720 same-sex adolescent siblings between 10 and 18 years of age consisting of monozygotic and dizygotic twins, full siblings, half siblings, and unrelated siblings. Composite measures of adolescent and parent reports and observational measures of depressive symptoms and antisocial behavior were subjected to behavioral genetic models that examine the genetic and environmental influences on individual differences in each dimension as well as in the co-occurrence between dimensions. Results indicated that approximately half of the variability in depressive symptoms and antisocial behavior is attributed to genetic factors; shared and nonshared environmental influences were also significant. The co-occurrence of depressive and antisocial symptoms was explained by genetic and shared and nonshared environmental influences. Specifically, approximately 45% of the observed covariation between depressive and antisocial symptoms could be explained by a common genetic liability. Results are interpreted in light of contribution of genetic studies to debates on child and adolescent psychopathology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Haviland, McGuire, and Rothbaum's "A critique of Plomin and Foch's twin study."

Replies to the criticism of J. M. Haviland et al (see record 1984-11539-001) of the present authors' (see record 1981-25190-001) twin study of objectively assessed personality in childhood. No merit is found in the criticisms of Haviland et al concerning conceptual validity and stability of the measures, comparability of populations, the accuracy of the literature review, or the appropriate interpretation of broad heritability. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parent ratings of EAS temperaments in twins, full siblings, half siblings, and step siblings.

A twin/family design was used to explore genetic contributions to personality; to evaluate whether twins and nontwins yield different genetic results; and to test for the presence of contrast effects, the tendency of a rater to contrast one sibling with the other, thereby magnifying existing behavioral differences. The sample consisted of 708 adolescent same-sex sibling pairs from 10 to 18 years of age. Pairs included identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins, and full siblings in nondivorced families; and full, half, and unrelated siblings in stepfamilies. Mothers and fathers rated the temperament of their children on the EAS Temperament Survey (A. H. Buss & R. Plomin, 1984). Model-fitting analyses revealed significant genetic infiuences on each of the four EAS dimensions; however, for some dimensions, heritability estimates were significantly greater for twins than for nontwins. Overall, the data were best described by a sibling interaction model, which indicated significant contrast effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic mediation of the home environment during infancy: A sibling adoption study of the HOME.

Recent research has demonstrated that measures of the environment show genetic mediation. This study examined resemblance of 105 nonadoptive and 85 adoptive sibling pairs from the Colorado Adoption Project on an objective measure of the environment (Home Observation for Measurement of the Environment [HOME]). Each sibling's home environment was assessed at 12 and 24 mo of age. Nonadoptive sibling correlations were greater than those for adoptive sibling pairs at both ages, suggesting genetic contributions on the HOME. In addition, the possibility was explored that bivariate associations between environment and outcome measures may be mediated genetically by using the HOME and N. Bayley's Mental Development Index (MDI). Phenotypic and cross-sibling correlations were greater for nonadoptive siblings than for adoptive pairs at age 2, suggesting genetic mediation of the HOME–MDI association. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A twin study of objectively assessed personality in childhood.

Obtained objectively assessed measures of activity, fidgeting, vigilance, selective attention, and aggression for a sample of 87 twin pairs in late childhood (mean age 7.6 yrs). Data included videotaped observations in standardized situations, objective test scores, and mechanical measures. Test–retest reliability was obtained for all measures. Contrary to results of questionnaire studies, there was little evidence for genetic influence on reliable and objective behavioral assessments. Also in disagreement with questionnaire studies, between-family environmental sources of variance were far more important than within-family factors. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)