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 etiology of variation in language skills changes with development: a longitudinal twin study of language from 2 to 12 years

The present study is the first long-term longitudinal examination of the etiology of individual differences in language from early childhood through to adolescence. We applied a multivariate latent factor genetic model to longitudinal data from the Twins Early Development Study in order to (a) compare the magnitude of genetic and environmental influences on language skills in early childhood (2, 3 and 4 years), middle childhood (7, 9 and 10 years), and early adolescence (12 years); and (b) determine to what extent the same genetic and environmental factors underlie variation in language skills at these three stages of language development. We found that while shared environmental influences appear to be dominant (latent factor c2 = .74) in early language, with a smaller though significant role for genetic factors (latent factor a2 = .24), the pattern is reversed by middle childhood such that genetic influences are substantially more important (latent factor a2 = .57-.63 at 7, 9 and 10 years and .47-.57 at 12 years) and shared environmental influences less so (latent factor c2 = .31-.37 at 7, 9 and 10 years and .31-.32 at 12 years). The increase in the heritability of language skills between early and middle childhood appears to be due to new genetic factors that come into play at that transition. In contrast, genetic factors remain stable from middle childhood through to early adolescence, and account for the phenotypic continuity in language skills across these two stages.     

Generalist genes and cognitive abilities in Chinese twins

This study considered how far nonverbal cognitive, language and reading abilities are affected by common genetic influences in a sample of 312 typically developing Chinese twin pairs aged from 3 to 11 years. Children were individually given tasks of Chinese word reading, receptive vocabulary, phonological memory, tone awareness, syllable and rhyme awareness, rapid automatized naming, morphological awareness and orthographic skills, and Raven's Colored Progressive Matrices. Factor analyses on the verbal tasks adjusted for age indicated two factors: Language as the first factor and Reading as the second factor. Univariate genetic analyses indicated that genetic influences were substantial for nonverbal cognitive ability and moderate for language and reading. Multivariate genetic analyses showed that nonverbal cognitive ability, language and reading were influenced by shared genetic origins, although there were specific genetic influences on verbal skills that were distinct from those on nonverbal cognitive ability. This study extends the Generalist Genes Hypothesis to Chinese language and reading skills, suggesting that the general effects of genes could be universal across languages.     

An exploration of genetic g: Hierarchical factor analysis of cognitive data from the western reserve twin project

Hierarchical factor analyses involving Schmid-Leiman transformations (Schmid & Leiman, 1957) were conducted on specific cognitive abilities data collected in a sample of 148 identical (MZ) and 135 same-sex fraternal (DZ) twin pairs. Two main questions were addressed: First, are genetic influences on specific cognitive abilities simply a reflection of their g loading, or are different sets of genes affecting separate abilities? Second, to the extent that specific cognitive abilities are affected by common genetic variance, how similar is the common genetic factor to a phenotypic factor reflecting g? Model fitting results suggest that genetic influences on specific abilities are a reflection of both general intelligence and genetic influences specific to separate abilities and that loadings on the common genetic factor are more highly correlated with phenotypic g loadings than are common environmental factor loadings.     

语言能力的老化机制：语言特异性与非特异性因素的共同作用

语言能力的衰退是由于一般认知能力衰退引起的, 还是由于语言加工系统的衰退引起的, 抑或是两者的共同作用?研究中测量了青年组和老年组的一般认知能力(加工速度、工作记忆和抑制能力), 以及在词汇、句子和语篇三个水平上的语言理解能力和语言产生能力。结果发现, 一般认知能力、语言理解和语言产生能力都存在年老化现象。分层回归分析表明, 一般认知能力对语言能力的贡献, 以及语言理解能力和产生能力之间的相互贡献在青年组和老年组中是不同的, 且存在词汇、句子和语篇水平上的差异。在词汇水平上, 青年人的成绩能够被一般认知能力和另一种语言能力所显著预测, 而老年人的成绩却不受一般认知因素影响; 在句子水平上, 青年人的成绩仍能被一般认知能力或另一种语言能力所解释, 但这两类变量都无法预测老年人的任务成绩; 在语篇水平上, 青年人理解任务的成绩显著地受到产生能力影响, 而老年人的理解和产生任务成绩则分别可以被一般认知能力和语言理解能力所解释。对组间差异的回归分析表明, 一般认知能力和另一种语言能力对组间差异都有显著贡献, 且前者的贡献大于后者。上述研究结果表明, 语言能力的老化是语言特异性因素和非特异性因素共同作用的结果。     

The construct of general intelligence

The construct of general intelligence is discussed in a number of different contexts. The fundamental empirical basis for it is the positive trend among the smallest correlations among cognitive measures. Differences among factor models which recognize this in different ways are discussed. Evidence for the general factor in intelligence is also found in the difficulty in finding evidence for differential validity of tests from one criterion to another. Performance on Piagetian tasks reflects mainly general intelligence. Individual differences in aural comprehension of language anticipate later individual differences in intellectual development. Selective forces which produce differences among schools operate largely on the general factor. To the extent that there is a genetic contribution to individual differences on cognitive tests, it appears to be to the general factor variance. Social class differences among whites appear to be largely on the general factor, but black-white differences require other dimensions. Although the general factor is, in a sense, real, it is not interpreted as an entity within the organism. Instead it is an abstraction resulting from the many genes, the many environmental pressures, and the many neural structures involved in the wide variety of human behaviors which can be labelled cognitive or intellectual.     

Genetic and environmental influences on pubertal development: longitudinal data from Finnish twins at ages 11 and 14

To study sources of individual differences in pubertal development, the authors fit a sex-limitation common factor model to data reported, at ages 11 and 14 years, by 1,891 twin pairs on items that comprise the Pubertal Development Scale (PDS; A. C. Petersen, L. Crockett, M. Richards, & A. Boxer, 1988). The model divides variation into a general pubertal factor and item-specific variation and, in addition, decomposes it into constituent sources. In both boys and girls, genetic influences made the largest contribution to variance common to PDS items. Genetic and nonshared environmental factors accounted for variation specific to PDS items in boys, whereas for girls, common environmental influences were added for growth spurt and menarcheal status. For both common and item-specific variation, genetic effects were partially sex specific. Subsidiary analyses found accelerated maturation in both boys and girls who at age 14 were reared in father-absent homes.     

Individual Differences in Early Scientific Thinking: Assessment,Cognitive Influences,and Their Relevance for Science Learning

ABSTRACT

Early scientific thinking in kindergarten (6-year-olds) was investigated in a large study involving 227 participants. We investigated (1) whether individual differences across 3 scientific-thinking components (experimentation, data interpretation, and understanding the nature of science) are stable across children, (2) whether children’s increased information-processing skills (intelligence, language abilities) and their development of an advanced theory of mind (AToM) are potential mechanisms that bring about individual differences in scientific thinking, and (3) whether individual differences in scientific thinking predict individual differences in science content knowledge. Using a newly developed instrument with 30 items (the Science-K inventory), we found that a one-dimensional Rasch model provides a good fit to the data, showing that kindergarteners’ scientific thinking goes beyond competencies in single tasks. Individual differences across the diverse scientific-thinking tasks were stable, and children’s scientific thinking was correlated with their intelligence and their language abilities. AToM was an important precursor for scientific thinking, predicting it independently from the influences of information-processing skills. Children’s science content knowledge was predicted by their score on the Science-K inventory. This finding points to a specific relation between these 2 components of scientific literacy, and it supports the view that scientific-thinking skills help to better test and revise (wrong) beliefs and misconceptions about science. Our study is the first to reveal substantial individual differences in scientific thinking in children as young as kindergarteners, and it shows that scientific thinking is important for a successful learning of science concepts, even before children enter formal schooling and begin science education.     

Between- versus within-family factor analyses of cognitive abilities

Confirmatory factor analyses of the 15 cognitive abilities tests from the Hawaii Family Study of Cognition were conducted on between-family (BF) means and within-family (WF) differences for 370 AEA (Americans of European ancestry) and 116 AJA (Americans of Japanese ancestry) sibling pairs. Difference chi-square significance tests, goodness-of-fit indices, and congruence coefficients for the estimated loadings on four specific cognitive abilities factors and on the second-order general intelligence factor nearly all indicated that the between-family factor structures were not significantly different from the within-family structures for both AEA and AJA siblings (the AEA and AJA structures were also not significantly different). The similarity of the BF and WF structures suggests that the genetic and environmental influences underlying cognitive abilities are “intrinsic” in nature, that is, not just due to between-family differences in culture, status, values, and fortuitous cross-assortative mating.     

Quantitative genetic analysis of latent growth curve models of cognitive abilities in adulthood

Though many cognitive abilities exhibit marked decline over the adult years, individual differences in rates of change have been observed. In the current study, biometrical latent growth models were used to examine sources of variability for ability level (intercept) and change (linear and quadratic effects) for verbal, fluid, memory, and perceptual speed abilities in the Swedish Adoption/Twin Study of Aging. Genetic influences were more important for ability level at age 65 and quadratic change than for linear slope at age 65. Expected variance components indicated decreasing genetic and increasing nonshared environmental variation over age. Exceptions included one verbal and two memory measures that showed increasing genetic and nonshared environmental variance. The present findings provide support for theories of the increasing influence of the environment with age on cognitive abilities.     

Domain-specific and domain-general constraints on word and sequence learning

The relative influences of language-related and memory-related constraints on the learning of novel words and sequences were examined by comparing individual differences in performance of children with and without specific deficits in either language or working memory. Children recalled lists of words in a Hebbian learning protocol in which occasional lists repeated, yielding improved recall over the course of the task on the repeated lists. The task involved presentation of pictures of common nouns followed immediately by equivalent presentations of the spoken names. The same participants also completed a paired-associate learning task involving word–picture and nonword–picture pairs. Hebbian learning was observed for all groups. Domain-general working memory constrained immediate recall, whereas language abilities impacted recall in the auditory modality only. In addition, working memory constrained paired-associate learning generally, whereas language abilities disproportionately impacted novel word learning. Overall, all of the learning tasks were highly correlated with domain-general working memory. The learning of nonwords was additionally related to general intelligence, phonological short-term memory, language abilities, and implicit learning. The results suggest that distinct associations between language- and memory-related mechanisms support learning of familiar and unfamiliar phonological forms and sequences.     

Path analysis of general and specific cognitive abilities in the Colorado adoption project: Early childhood

A path model of genetic and environmental transmission was fitted to general and specific cognitive abilities (verbal, spatial, visual memory, and perceptual speed) data from biological, adoptive, and control parents and their children at ages 3 and 4. Using a maximum-likelihood estimation procedure. the significance of genetic influence, passive genotype-environment correlation, parental influence on the child's environment, assortative mating, and selective placement was assessed. As predicted, the parameter estimate for genetic influence (a function of the heritabilities of the character during early childhood and adulthood and their genetic correlation) is significant for general cognitive ability at both 3 and 4. Moreover, estimates of the genetic parameter are significant for spatial ability at both 3 and 4 years of age, for verbal ability at 3, and for perceptual speed at 4. Thus, there is at least some continuity between early childhood and adulthood as well as some genetic differentiation for specif cognitive abilities.     

Multivariate genetic analysis of specific cognitive abilities in the Colorado adoption project at age 7

A multivariate hierarchical model of specific cognitive abilities was fitted to data from 7-year-old adopted and nonadopted sibling pairs in the Colorado Adoption Project in order to assess differential genetic influence on specific mental abilities. Model fitting results and Schmid-Leiman (Schmid & Leiman, 1957) transformations reveal significant heritable variation for verbal, spatial, and memory factors independent of general cognitive ability for the eight ability tests examined. In contrast, environmental influences are primarily measure-specific. The results suggest genetic effects in middle childhood that differentially influence mental ability scores.     

Individual differences in executive functions are almost entirely genetic in origin

Recent psychological and neuropsychological research suggests that executive functions--the cognitive control processes that regulate thought and action--are multifaceted and that different types of executive functions are correlated but separable. The present multivariate twin study of 3 executive functions (inhibiting dominant responses, updating working memory representations, and shifting between task sets), measured as latent variables, examined why people vary in these executive control abilities and why these abilities are correlated but separable from a behavioral genetic perspective. Results indicated that executive functions are correlated because they are influenced by a highly heritable (99%) common factor that goes beyond general intelligence or perceptual speed, and they are separable because of additional genetic influences unique to particular executive functions. This combination of general and specific genetic influences places executive functions among the most heritable psychological traits. These results highlight the potential of genetic approaches for uncovering the biological underpinnings of executive functions and suggest a need for examining multiple types of executive functions to distinguish different levels of genetic influences.     

Academic achievement in Blacks and Whites: Are the developmental processes similar?

Genetic and environmental influences on academic achievement were investigated in four groups of siblings: (1) White full siblings, (2) White half-siblings, (3) Black full siblings, and (4) Black half-siblings. Our expectation was that the variances and covariances among three achievement tests would have the same structure across the four groups. This expectation was confirmed by a quantitative genetic model that imposed equal factor loadings across groups. This best fitting model had two factors: a Genetic factor representing genetic variation and a Shared Environment factor representing environmental differences among families. Reading recognition, reading comprehension, and mathematics tests all loaded on the Genetic factor, but primarily mathematics loaded on the Shared Environment factor. The quantitative genetic model was next fit to the achievement test means. Its successful fit suggested that the genetic and environmental influences involved in producing individual variation were the same as those producing the group-mean differences. In this sample, genes accounted for 66% to 74% of the observed group difference in verbal achievement and 36% of the difference in mathematics achievement. Shared environment accounted for the remainder, 34% to 26% of the difference in verbal achievement and 64% of that in mathematics achievement.     

Infants’ sense of approximate numerosity: Heritability and link to other concurrent traits

The ability to perceive approximate numerosity is present in many animal species, and emerges early in human infants. Later in life, it is moderately heritable and associated with mathematical abilities, but the etiology of the Approximate Number System (ANS) and its degree of independence from other cognitive abilities in infancy is unknown. Here, we assessed the phenotypic specificity as well as the influence of genetic and environmental factors on the ANS in a sample of 5-month-old twins (N = 514). We found a small-to-moderate but statistically significant effect of genetic factors on ANS acuity (heritability = 0.18, 95% CI: 0.02, 0.33), but only when differences in numerosity were relatively large (1:4 ratio). Non-verbal ability assessed with the Mullen Scales of Early Learning (MSEL) was found to be heritable (0.47; 95% CI: 0.34, 0.57) and the phenotypic association between ANS acuity and non-verbal ability performance was close to zero. Similarly, we found no association between ANS acuity and general attention during the task. An unexpected weak but statistically significant negative association between ANS acuity and scores on the receptive language scale of the MSEL was found. These results suggest that early ANS function may be largely independent from other aspects of non-verbal development. Further, variability in ANS in infancy seems to, to some extent, reflect genotypic differences in the population.

Highlights

• Assessing 514 infant twins with eye tracking, we found that infants' sense of approximate numerosity is heritable and not positively associated with concurrent attentional, cognitive or motor abilities.
• These results have implications for our understanding of development of mathematical ability and the link between cognitive abilities early in postnatal life.

     

The Genetic and Environmental Relationship Between General and Specific Cognitive Abilities in Twins Age 80 and Older

In the first twin study of the old-old, individuals 80 years old and older, we examined the relationship between general and specific cognitive abilities from a genetic perspective. That is, we examined the extent to which genetic and environmental factors influence major group factors of cognitive abilities, independent of general cognitive ability. As part of the OctoTwin project in Sweden, general and specific cognitive abilities were assessed in 52 monozygotic and 65 same-sex dizygotic twin pairs 80 years old and older using a battery of seven tests that assess verbal, spatial, speed-of-processing, and memory performance. Results suggest that genetic effects associated with general cognitive ability ( g ) account for the correlation between g and verbal, spatial, and speed-of-processing abilities. No genetic influences were found for these specific cognitive abilities separate from g . In contrast, memory ability appears to be more distinct genetically from g than are other cognitive abilities. Comparison with younger samples suggests that cognitive abilities relating to speed of processing may be genetically dedifferentiated in the old-old.     

Counterproductive behaviors: Relations across life domains,etiology, and implications for applied practice

Previous research on counterproductive work behavior (CWB) has shown that workplace deviance can be predicted from individual differences and environmental variables, but relatively little is known about CWBs’ relations with counterproductive behaviors in other domains of an individual's life. Data from 500 male twins were used to examine relations among counterproductive behaviors from several life domains, including school, non‐work, substance use, and work. The results supported the hypotheses that counterproductivity in work and a variety of personal life domains, previous and contemporaneous, are strongly and positively related. A general counterproductivity factor, giving rise to rule‐ and norm‐breaking behavioral repertoire of individuals, accounted for approximately half the variance across measures of counterproductivity in specific life domains. To inform theory and research, the etiology of inter‐individual differences in counterproductivity was examined. Biometric analyses revealed that most of the variance in the counterproductivity domains examined, including CWB, is attributable to genetic and unique (nonshared) environmental factors. The general counterproductivity factor spanning different counterproductivity domains was most influenced by genetic factors (75.4%), but was also influenced by unique environmental factors (24.6%). Biometric analyses indicated that 27% of the variance in CWB is attributable to genetic influences arising from the general factor of counterproductivity and 20% from genetic factors specific to CWB. Unique environmental influences associated with the work domain explained 12% of the variance in CWB. For the CWB criterion, regression analyses explored the usefulness of information from other counterproductivity domains for prediction and employee selection. Counterproductivity from academic and non‐work domains are potent predictors of counterproductivity at work (multiple Rs ranging between .50 and .54).