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Editor's note: gleaned from a Usenet posting compiled by Michael Kagalenko from a Medline search.

J Child Psychol Psychiatry 36: 409-425 (1995)[95301642]

The impact of child IQ, parent IQ and sibling IQ on child behavioural deviance scores.

R. Goodman, E. Simonoff & J. Stevenson

Department of Child and Adolescent Psychiatry, Institute of Psychiatry, London, U.K.

In an epidemiological sample of 411 13-year-old twins of normal intelligence, both parents and teachers reported more behavioural problems among children with lower IQs. This was not attributable to the effects of parental IQ or social class and was not entirely mediated by lower scholastic attainments. Different causal models are discussed: "rater bias" and "IQ is a consequence" explanations seem less plausible than "IQ is a cause" and "IQ is a marker" explanations. Higher parental IQ was associated with more emotional symptoms in the child, both by parental and school report. There was no evidence that being brighter or less bright than a (twin) sibling influenced behavioural deviance, casting doubt on the importance of contrast effects.

Behav Genet 25: 25-32 (1995)[95275182]

Multivariate genetic analysis of Wechsler Intelligence Scale for Children--Revised (WISC-R) factors.

S. D. Casto, J. C. DeFries & D. W. Fulker

Institute for Behavioral Genetics, University of Colorado at Boulder 80309-0447, USA.

Wechsler Intelligence Scale for Children--Revised (WISC-R) factor scores (Verbal Comprehension, Perceptual Organization, and Freedom from Distractibility) were obtained from 574 twin pairs in the Colorado Reading Project and subjected to multivariate genetic analysis. Variances were partitioned into components common to the three WISC-R factors and to those specific to each factor. Substantial commonality, both genetic and environmental, was found among the three factors. The full model fit the data well, and estimates of heritability and environmentality indicated that about half of the phenotypic variance for each factor is due to additive genetic effects. These results were compared to those obtained in a previous twin study of the three Wechsler Adult Intelligence Scale (WAIS) factors by Tambs et al. (1986).

Behav Genet 24: 107-118 (1994)[94296350]

DNA markers associated with high versus low IQ: the IQ Quantitative Trait Loci (QTL) Project.

R. Plomin, G. E. McClearn, D. L. Smith, S. Vignetti, M. J. Chorney, K. Chorney, C. P. Venditti, S. Kasarda, L. A. Thompson, D. K. Detterman & ...

Center for Developmental and Health Genetics, Pennsylvania State University, University Park 16802.

General cognitive ability (intelligence, often indexed by IQ scores) is one of the most highly heritable behavioral dimensions. In an attempt to identify some of the many genes (quantitative trait loci; QTL) responsible for the substantial heritability of this quantitative trait, the IQ QTL Project uses an allelic association strategy. Allelic frequencies are compared for the high and low extremes of the IQ dimension using DNA markers in or near genes that are likely to be relevant to neural functioning. Permanent cell lines have been established for low-IQ (mean IQ = 82; N = 18), middle-IQ (mean IQ = 105; N = 21), and high-IQ (mean IQ = 130; N = 24) groups and for a replication sample consisting of even more extreme low-IQ (mean IQ = 59; N = 17) and high-IQ (mean IQ = 142; N = 27) groups. Subjects are Caucasian children tested from 6 to 12 years of age. This first report of the IQ QTL Project presents allelic association results for 46 two-allele markers and for 26 comparisons for 14 multiple-allele markers. Two markers yielded significant (p < .01) allelic frequency differences between the high- and the low-IQ groups in the combined sample-a new HLA marker for a gene unique to the human species and a new brain-expressed triplet repeat marker (CTGB33). The prospects for harnessing the power of molecular genetic techniques to identify QTL for quantitative dimensions of human behavior are discussed.

Psychol Rep 71: 811-21 (1992)[93087680]

Contributions to the history of psychology: XC. Evolutionary biology and heritable traits (with reference to oriental-white-black differences): the 1989 AAAS paper.

J. P. Rushton

Department of Psychology, University of Western Ontario, London, Canada.

Genetic distance estimates calculated from DNA sequencing indicate that in years since emergence from the ancestral hominid line, Mongoloids = 41,000, Caucasoids = 110,000, and Negroids = 200,000. Data also show that this succession is matched by numerous other differences such that Mongoloids > Caucasoids > Negroids in brain size and intelligence (cranial capacity = 1448, 1408, 1334 cm3; brain weight = 1351, 1336, 1286 gm.; millions of excess neurons = 8900, 8650, 8550; IQ = 107, 100, 85); maturational delay (age to walk alone, age of first intercourse, age of death); sexual restraint (ovulation rate, intercourse frequencies, sexually transmitted diseases including AIDS); quiescent temperament (aggressiveness, anxiety, sociability); and social organization (law abidingness, marital stability, mental health). This pattern is ordered by a theory of r/K reproductive strategies in which Mongoloids are posited to be more K-selected than Caucasoids and especially more than Negroids. (K-selected reproductive strategies emphasize parental care and are to be contrasted with r-selected strategies which emphasize fecundity, the bioenergetic trade-off between which is postulated to underlie cross-species differences in brain size, speed of maturation, reproductive effort, and longevity.) It is suggested that this pattern came about because the ice ages exerted greater selection pressures on the later emerging populations to produce larger brains, longer lives, and more K-like behavior. One theoretical possibility is that evolution is progressive and that some populations are more "advanced" than others. Predictions are made concerning economic projections and the spread of AIDS.

Behav Genet 21: 351-67 (1991)[92061889]

The genetic correlation between intelligence and speed of information processing.

L. A. Baker, P. A. Vernon & H. Z. Ho

Department of Psychology, University of Southern California, Los Angeles 90089.

This study examined the contributions of genetic and environmental factors to the observed correlation between intelligence test scores and speed of information processing, based on data for same-sex adult twin pairs (age, 15-57). Verbal and performance IQ scores from the Multidimensional Abilities Battery, as well as 11 reaction-time measures derived from a battery of information-processing tasks, were available for 50 monozygotic and 32 dizygotic pairs of twins. Multivariate biometrical analyses were used to estimate genetic and environmental parameters underlying observed variances and covariances among intelligence test scores and a general speed of information-processing factor (based on a linear composite of the 11 reaction-time scores). A common-factor model with loadings on general speed of processing, verbal IQ, and performance IQ fit the data well. The common factor was influenced primarily by additive genetic effects, such that the observed relationships among the speed and IQ measures are mediated entirely by hereditary factors. There was additional specific genetic variance for Verbal IQ and specific shared-twin environmental variance for Performance IQ. However, twin similarity for general speed of processing was explained entirely by genetic factors related to intelligence. The results emphasize the importance of common, heritable, biological mechanisms underlying the speed-IQ association.

Nature 309: 620-2 (1984)[84219770]

Heredity and familial environment in intelligence and educational level--a sibling study.

T. W. Teasdale & D. R. Owen

Although it is well established that family members resemble each other in intelligence , the extent to which this results from either shared genes or a shared environment remains controversial, perhaps especially since the relevant evidence presented by Burt has been shown probably to have been fabricated. The influence of heredity and familial environment may be distinguished by studying adoptees. Here we present correlations in intelligence and educational level between genetically related pairs of adult adoptees who have been reared separately, and, conversely, between genetically unrelated pairs of adult adoptees who have been reared together. We are unaware of any previous study of adults which has reported on both of these types of relationship. The results for intelligence conform closely to what would be predicted by a simple polygenic model of genetic transmission whereas those for educational attainment imply both genetic and familial environmental components.

Child Dev 54: 268-75 (1983)[83260799]

The Texas Adoption Project: adopted children and their intellectual resemblance to biological and adoptive parents.

J. M. Horn

Intelligence test scores were obtained from parents and children in 300 adoptive families and compared with similar measures available for the biological mothers of the same adopted children. Results supported the hypothesis that genetic variability is an important influence in the development of individual differences for intelligence. The most salient finding was that adopted children resemble their biological mothers more than they resemble the adoptive parents who reared them from birth. A small subset of the oldest adopted children did not resemble their biological mothers. The suggestion that the influence of genes declines with age is treated with caution since other adoption studies report a trend in the opposite direction.

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