Although common sense suggests that environmental influences increasingly account for individual differences in behavior as experiences accumulate during the course of life, this hypothesis has not ...previously been tested, in part because of the large sample sizes needed for an adequately powered analysis. Here we show for general cognitive ability that, to the contrary, genetic influence increases with age. The heritability of general cognitive ability increases significantly and linearly from 41% in childhood (9 years) to 55% in adolescence (12 years) and to 66% in young adulthood (17 years) in a sample of 11 000 pairs of twins from four countries, a larger sample than all previous studies combined. In addition to its far-reaching implications for neuroscience and molecular genetics, this finding suggests new ways of thinking about the interface between nature and nurture during the school years. Why, despite life's 'slings and arrows of outrageous fortune', do genetically driven differences increasingly account for differences in general cognitive ability? We suggest that the answer lies with genotype-environment correlation: as children grow up, they increasingly select, modify and even create their own experiences in part based on their genetic propensities.
General and specific cognitive abilities were studied in intact Swedish same-sex twin pairs 80 or more years old for whom neither twin had major cognitive, sensory, or motor impairment. Resemblance ...for 110 identical twin pairs significantly exceeded resemblance for 130 fraternal same-sex twin pairs for all abilities. Maximum-likelihood model-fitting estimates of heritability were 62 percent for general cognitive ability, 55 percent for verbal ability, 32 percent for spatial ability, 62 percent for speed of processing, and 52 percent for memory. There was also evidence for the significant influence of idiosyncratic experience as the environmental component that most determines individual differences in cognitive abilities late in life.
Background: To what extent do genetic and environmental influences on reading disability overlap with those on mathematics disability? Multivariate genetic research on the normal range of variation ...in unselected samples has led to a Generalist Genes Hypothesis which posits that the same genes largely affect individual differences in these abilities in the normal range. However, little is known about the etiology of co‐morbidity for the disability extremes of reading and mathematics.
Method: From 2596 pairs of 10‐year‐old monozygotic and dizygotic twins assessed on a web‐based battery of reading and mathematics tests, we selected the lowest 15% on reading and on mathematics. We conducted bivariate DeFries–Fulker (DF) extremes analyses to assess overlap and specificity of genetic and environmental influences on reading and mathematics disability defined by a 15% cut‐off.
Results: Both reading and mathematics disability are moderately heritable (47% and 43%, respectively) and show only modest shared environmental influence (16% and 20%). There is substantial phenotypic co‐morbidity between reading and mathematics disability. Bivariate DF extremes analyses yielded a genetic correlation of .67 between reading disability and mathematics disability, suggesting that they are affected largely by the same genetic factors. The shared environmental correlation is .96 and the non‐shared environmental correlation is .08.
Conclusions: In line with the Generalist Genes Hypothesis, the same set of generalist genes largely affects mathematical and reading disabilities. The dissociation between the disabilities occurs largely due to independent non‐shared environmental influences.
Basic intellectual abilities of quantity and numerosity estimation have been detected across animal species. Such abilities are referred to as ‘number sense’. For human species, individual ...differences in number sense are detectable early in life, persist in later development, and relate to general intelligence. The origins of these individual differences are unknown. To address this question, we conducted the first large-scale genetically sensitive investigation of number sense, assessing numerosity discrimination abilities in 837 pairs of monozygotic and 1422 pairs of dizygotic 16-year-old twin pairs. Univariate genetic analysis of the twin data revealed that number sense is modestly heritable (32%), with individual differences being largely explained by non-shared environmental influences (68%) and no contribution from shared environmental factors. Sex-Limitation model fitting revealed no differences between males and females in the etiology of individual differences in number sense abilities. We also carried out Genome-wide Complex Trait Analysis (GCTA) that estimates the population variance explained by additive effects of DNA differences among unrelated individuals. For 1118 unrelated individuals in our sample with genotyping information on 1.7million DNA markers, GCTA estimated zero heritability for number sense, unlike other cognitive abilities in the same twin study where the GCTA heritability estimates were about 25%. The low heritability of number sense, observed in this study, is consistent with the directional selection explanation whereby additive genetic variance for evolutionary important traits is reduced.
•Modest heritability of numerosity discrimination skills at 16 years•GCTA analysis supports directional selection for numerosity discrimination skills.•No sex differences in the etiology of individual variation in numerosity at age 16
Mathematics performance at 7 years as assessed by teachers using UK national curriculum criteria has been found to be highly heritable. For almost 3000 pairs of 7-year-old same-sex twins, we used ...multivariate genetic analysis to investigate the extent to which these genetic effects on mathematics performance overlap with genetic effects on reading and general intelligence (g) as predicted by the ‘generalist genes’ hypothesis. We found substantial genetic overlap between mathematics and reading (genetic correlation
=
0.74) and between mathematics and g (0.67). These findings support the ‘generalist genes’ hypothesis that most of the genes that contribute to individual differences in mathematics are the same genes that affect reading and g. Nonetheless, the genetic correlations are less than unity and about a third of the genetic variance on mathematics is independent of reading and g, suggesting that there are also some genes whose effects are specific to mathematics.
Numeracy is as important as literacy and exhibits a similar frequency of disability. Although its etiology is relatively poorly understood, quantitative genetic research has demonstrated mathematical ...ability to be moderately heritable. In this first genome‐wide association study (GWAS) of mathematical ability and disability, 10 out of 43 single nucleotide polymorphism (SNP) associations nominated from two high‐ vs. low‐ability (n = 600 10‐year‐olds each) scans of pooled DNA were validated (P < 0.05) in an individually genotyped sample of *2356 individuals spanning the entire distribution of mathematical ability, as assessed by teacher reports and online tests. Although the effects are of the modest sizes now expected for complex traits and require further replication, interesting candidate genes are implicated such as NRCAM which encodes a neuronal cell adhesion molecule. When combined into a set, the 10 SNPs account for 2.9% (F = 56.85; df = 1 and 1881; P = 7.277e–14) of the phenotypic variance. The association is linear across the distribution consistent with a quantitative trait locus (QTL) hypothesis; the third of children in our sample who harbour 10 or more of the 20 risk alleles identified are nearly twice as likely (OR = 1.96; df = 1; P = 3.696e–07) to be in the lowest performing 15% of the distribution. Our results correspond with those of quantitative genetic research in indicating that mathematical ability and disability are influenced by many genes generating small effects across the entire spectrum of ability, implying that more highly powered studies will be needed to detect and replicate these QTL associations.
Background: Parent–child mutuality is comprised of emotional reciprocity, co‐responsiveness, and cooperation, which together represent aspects of co‐regulation of emotion and behavior that may be ...important in the etiology of children's behavior problems. Furthermore, individual differences in children's mutuality and behavior problems involve transactions between genetic and environmental influences. Behavioral genetic designs are useful for elucidating these processes.
Methods: The sample included 396 children in adoptive families (53% female, age M = 8.16 years), of whom 244 were siblings (122 pairs). All of the siblings were genetically unrelated. In some families, one child was adopted but the other child was a biological child of the adoptive parents. We observed mother–child dyadic mutuality (a composite score including responsiveness, interaction reciprocity, and cooperation) during videotaped in‐home observations. In addition, child behavior problems were assessed and represented as a composite score including observers’ ratings of noncompliance, and parents’ ratings of aggression and conduct problems.
Results: Greater mutuality was associated with lower levels of child behavior problems, both between families and within families (i.e., sibling differences). The sibling intra‐class correlation for mutuality with the same parent was near zero in this sample of genetically unrelated siblings. The correlation between child behavior problems and dyadic mutuality did not vary as a function of mother–child genetic similarity.
Conclusions: Mother–child mutuality is child specific within families, a finding that is consistent with theories regarding bi‐directional parent and child effects in socialization. In addition, there was no evidence of passive gene–environment correlation, suggesting that the link between lower levels of maternal mutuality and higher levels of childbehavior problems is not only reflecting overlapping genetic influences on parent and child behavior.
The current study involved 281 early-school-age twin pairs (118 monozygotic, 163 same-sex dizygotic) participating in the ongoing Western Reserve Reading Project (
S. A. Petrill, K. Deater-Deckard, ...L. A. Thompson, & C. Schatschneider, 2006
). Twins were tested in their homes by separate examiners on a battery of reading-related skills including phonological awareness, rapid automatized naming, word knowledge, and phonological decoding. Results suggested that a core genetic factor accounted for a significant portion of the covariance between phonological awareness, rapid naming, and reading outcomes. However, shared environmental influences related to phonological awareness were also associated with reading skills.
This study examined shared environmental influences on the longitudinal stability of general cognitive ability, as mediated by socioeconomic status and chaos in the home, using 287 pairs of ...elementary school-age twins drawn from the Western Reserve Reading Project (WRRP). General cognitive ability was evaluated at two annual assessments using the Stanford-Binet Intelligence Test. SES was examined using the highest level of education achieved by the mother of the twins, and chaos by a 6-item parent-report questionnaire. Results suggest that SES and CHAOS not only account for independent sources of shared environmental influences related to general cognitive ability at a given measurement occasion, but these effects also account for a portion of the longitudinal stability of general cognitive ability in early childhood.
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