Sources of continuity and change in activity level in early childhood

Using the Flanker Task to Examine Genetic and Environmental Contributions in Inhibitory Control Across the Preschool Period

The limited research exploring genetic and environmental influences on inhibitory control (IC) in preschoolers has relied on parent ratings or simple delay tasks and has produced mixed results. The present study uses a cognitively-challenging Flanker task to examine genetic and environmental contributions to the development of early IC in a longitudinal sample of 310 same-sex twin pairs (123 MZ; 187 DZ; 51% female) assessed at ages 3, 4 and 5 years. IC was significantly heritable at each age (a²: age 3 = .36; age 4 = .36; age 5 = .35). Stability was entirely accounted for by genetic influences, and change was explained by genetic and nonshared environmental factors. No significant shared environmental influences were observed.

Trait continuity: Can parent-rated infant temperament predict HEXACO personality in early adulthood?

Examining the Raine cohort study, we tested the trait continuity hypothesis by examining the extent that young adults' (25-29 years old) self-reported HEXACO personality can be statistically predicted from multi-dimensional parental temperament ratings collected in infancy (1-2 years old). The study incorporated a lagged design (two waves), a large sample size (n = 563), and examined both temperament and personality as both dimensions and profiles. Overall, we found very limited evidence of trait continuity, with generally very weak and few statistically significant observed associations of infant temperament with early adulthood personality. Relations were weak whether profile or dimension-based operationalizations of both phenomena were adopted. Additionally, controlling for sex affected the relations of temperament and personality only to a small extent for most of the traits, and moderation effects of sex were generally zero-to-trivial in size. Altogether, parent-rated temperament in infancy seems to provide little information about HEXACO personality in early adulthood.

Genetic and environmental influences on temperament development across the preschool period

BACKGROUND

Preschoolers' temperament characteristics are associated with children's long-term development. Such links underscore the importance of understanding factors that shape temperament during preschool. This is the first study to examine genetic and environmental sources of developmental growth in three temperament dimensions: surgency, negative affectivity, and effortful control, during the preschool period.

METHODS

Biometric latent growth curve modeling was used to examine genetic, shared, and nonshared environmental contributions to the invariant level of and developmental growth in temperament, using a sample of 310 same-sex twin pairs (MZ = 123, DZ = 187) assessed at 3, 4, and 5 years of age. Temperament was assessed using primary caregiver's report on the Child Behavior Questionnaire-Short Form.

RESULTS

All three temperament dimensions demonstrated linear increases from ages 3 to 5 years. The invariant levels of all three temperament dimensions were explained by genetic and nonshared environmental factors. Growth in surgency was fully explained by nonshared environmental factors, while growth in negative affectivity was mainly explained by genetic factors. Growth in effortful control was explained by genetic and nonshared environmental factors, although neither were significant due to large bootstrap standard errors. For negative affectivity and effortful control, the genetic factors that contributed to developmental growth were independent from those associated with their invariant levels.

CONCLUSIONS

Collectively, these findings indicate that both genetic and nonshared environmental factors play important roles in the invariant levels of temperament. Findings also accord a critical role of children's nonshared environment in the development of surgency and to a lesser extent negative affectivity and effortful control. It is also notable that novel genetic effects contribute to developmental growth in negative affectivity and effortful control as children age, emphasizing the importance of integrating developmental models in genetic research.

Heritability of Psychological Traits and Developmental Milestones in Infancy: A Systematic Review and Meta-analysis

Importance

Although infancy is the most rapid period of postnatal growth and development, factors associated with variation in infant traits are not well understood.

Objective

To synthesize the large twin study literature partitioning phenotypic variance in psychological traits and developmental milestones in infancy into estimates of heritability and shared and nonshared environment.

Data Sources

PubMed, PsycINFO, and references of included publications were searched up to February 11, 2021.

Study Selection

Peer-reviewed publications using the classical twin design to study psychological traits and developmental milestones from birth to 2 years old were included.

Data Extraction and Synthesis

Data were extracted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses and categorized using the International Classification of Functioning, Disability and Health: Children and Youth Version. Data were pooled in 3-level random effects models, incorporating within-cohort variance in outcome measurement and between-cohort variance. Data were analyzed from March 2021 through September 2021.

Main Outcomes and Measures

The primary outcomes were monozygotic and dizygotic twin correlations. These were used to calculate genetic and shared and nonshared environment estimates.

Results

Among 139 publications that were systematically retrieved, data were available on 79 044 twin pairs (31 053 monozygotic and 47 991 dizygotic pairs), 52 independent samples, and 21 countries. Meta-analyses were conducted on psychological traits and developmental milestones from 106 publications organized into 10 categories of functioning, disability, and health. Moderate to high genetic estimates for 8 categories were found, the highest of which was psychomotor functions (pooled h2, 0.59; 95% CI, 0.25-0.79; P < .001). Several categories of traits had substantial shared environment estimates, the highest being mental functions of language (pooled c2, 0.59; 95% CI, 0.24-0.86; P = .001). All examined categories of traits had moderate or high nonshared environment estimates, the highest of which were emotional functions (pooled e2, 0.42; 95% CI, 0.33-0.50; P < .001) and family relationships (pooled e2, 0.42; 95% CI, 0.30-0.55; P < .001).

Conclusions and Relevance

These findings may be an important source of information to guide future gene discovery research, public perspectives on nature and nurture, and clinical insights into the degree to which family history and environments may estimate major domains of infant functioning, disability, and health in psychological traits and developmental milestones.

Stabilities of Infant Behaviors and Maternal Responses to Them

Consistency in the order of individuals in a group across substantial lengths of time-stability-is a central concept in developmental science for several reasons. Stability underscores the meaningfulness of individual differences in psychological phenomena; stability informs about the origins, nature, and overall developmental course of psychological phenomena; stability signals individual status and so affects the environment, experience, and development; stability has both theoretical and clinical implications for individual functioning; and stability helps to establish that a measure constitutes a consequential individual-differences metric. In this three-wave prospective longitudinal study (Ns = 40 infants and mothers), we examined stabilities of individual variation in multiple infant behaviors and maternal responses to them across infant ages 10, 14, and 21 months. Medium to large effect size stabilities in infant behaviors and maternal responses emerged, but both betray substantial amounts of unshared variance. Documenting the ontogenetic trajectories of infant behaviors and maternal responses helps to elucidate the nature and structure of early human development.

Infant behaviors and maternal parenting practices: Short-term reliability assessments

Consistency in the order of individuals in a group across short periods of time-reliability-is both important developmentally and meaningful psychologically. For example, documenting the reliabilities of infant behaviors and maternal parenting practices elucidates the nature and structure of early development. In this prospective short-term longitudinal study (Ns = 51 5-month infants and their mothers), we examined reliabilities of individual variation in multiple infant behaviors (physical development, social interaction, exploration, nondistress vocalization, and distress communication) and maternal parenting practices (nurturing, encouragement of motor growth, social exchange, didactic interaction, provision of the material environment, and speech to infant). Medium to large effect size reliabilities characterize infant behaviors and maternal parenting practices, but both betray substantial amounts of unshared variance. Established reliability is essential to the application of these measures in infancy studies, it is central to replication, and it is a limiting factor in predictive validity.

The Boston University Twin Project (BUTP) II

The Boston University Twin Project (BUTP) uses a multimethod, longitudinal approach to study the role of genetic and environmental factors on the development of child temperament and related behaviors in early childhood. There are two phases in this project. The first, described in the previous Twin Research and Human Genetics special issue on twin registries, focused on activity level and comprised over 300 twin pairs assessed in the home and laboratory at ages 2 and 3. In this article, we describe subject recruitment, sample characteristics, and study procedures and measures of the second phase of the BUTP. This recent study focuses more broadly on the development of multiple temperament dimensions and explores associations between temperament trajectories, parenting and child adjustment in a new cohort of approximately 300 twin pairs assessed at 3, 4 and 5 years of age.

Stability of child temperament: Multiple moderation by child and mother characteristics

This 3-wave longitudinal study focuses on stability of child temperament from 3 to 6 years and considers child age, gender, birth order, and term status as well as mother age, education, anxiety, and depression as moderators of stability. Mothers of approximately 10,000 children participating in the Avon Longitudinal Study of Parents and Children rated child temperament. Stability coefficients for child temperament scales were medium to large, and stability was generally robust across moderators except child gender and birth order and mother age and education, which had small moderating effects on reports of stability of child temperament. Statement of contribution What is already known on this subject? Some is known about the stability of temperament in infancy in small samples, but much less is known about the stability of temperament in early childhood or its moderation. What does this study add? This study uses a large sample (˜10,000) to trace the stability of temperament from 3 to 6 years in three waves and considers child age, gender, birth order, and term status as well as mother age, education, anxiety, and depression as moderators of stability.

Parent- and Observer-Rated Positive Affect in Early Childhood: Genetic Overlap and Environmental Specificity

The sources of individual differences in both observed and parent-rated positive affect (PA) were examined in a sample of 304 3-year-old twin pairs (140 MZ, 164 DZ). Based on model-fitting analyses, individual differences in observed PA were attributed to moderate genetic and high nonshared environmental factors, but not shared environmental factors. In contrast, shared environmental effects accounted for over half of the variance in parent-rated PA and genetic and nonshared environmental effects were more modest. The genetic correlation across the two measures was high, indicating substantial overlap between genetic factors influencing the two. It was these overlapping genetic effects that fully explained the phenotypic correlation between both measures. There was no significant covariance between the environmental influences on parent rated and observed PA. Thus, the two measures of PA in early childhood have common genetic underpinnings, whereas environmental influences are measure-specific. Measurement implications are discussed.

Genetic and environmental links between motor activity level and attention problems in early childhood

Cross-lagged biometric models were used to examine genetic and environmental links between actigraph-assessed motor activity level (AL) and parent-rated attention problems (AP) in 314 same-sex twin pairs (MZ = 145, DZ = 169) at ages 2 and 3 years. At both ages, genetic correlations between AL and AP were moderate (ra2 = .35; ra3 = .39) indicating both overlap and specificity in genetic effects across the two domains. Within- and across-age phenotypic associations between AL and AP were entirely due to overlapping genetic influences. There was a unidirectional effect of AL at age 2 predicting later AP. For AP, genetic and environmental influences from age 2 were transmitted to age 3 via stability effects and from AL. For AL, across-age effects were transmitted only via stability. These results suggest that overactivity in late infancy may impact the later development of problems related to inattention, and that genetic factors explain the association between the two domains.

The Infant Version of the Laboratory Temperament Assessment Battery (Lab-TAB): Measurement Properties and Implications for Concepts of Temperament

We describe large-sample research using the Infant Laboratory Temperament Assessment Battery (Lab-TAB; Goldsmith and Rothbart, 1996) in 1,076 infants at 6 and 12 months of age. The Lab-TAB was designed to assess temperament dimensions through a series of episodes that mimic everyday situations. Our goal is to provide guidelines for scoring Lab-TAB episodes to derive temperament composites. We also present a set of analyses examining mean differences and stability of temperament in early infancy, gender differences in infant temperament, as well as a validation of Lab-TAB episodes and composites with parent reported Infant Behavior Questionnaire (IBQ; Rothbart, 1981) scales. In general, laboratory observed temperament was only modestly related to parent reported temperament. However, temperament measures were significantly stable across time and several gender differences that align with previous research emerged. In sum, the Lab-TAB usefully assesses individual differences in infant emotionality.

Tipping points? Curvilinear associations between activity level and mental development in toddlers

BACKGROUND

The Theory of Optimal Stimulation (Zentall & Zentall, Psychological Bulletin, 94, 1983, 446) posits that the relation between activity level (AL) and cognitive performance follows an inverted U shape where midrange AL predicts better cognitive performance than AL at the extremes.

METHODS

We explored this by fitting linear and quadratic models predicting mental development from AL assessed via multiple methods (parent ratings, observations, and actigraphs) and across multiple situations (laboratory play, laboratory test, home) in over 600 twins (2- and 3-year olds).

RESULTS

Only observed AL in the laboratory was curvilinearly related to mental development scores. Results replicated across situations, age, and twin samples, providing strong support for the optimal stimulation model for this measure of AL in early childhood.

CONCLUSIONS

Different measures of AL provide different information. Observations of AL which include both qualitative and quantitative aspects of AL within structured situations are able to capture beneficial aspects of normative AL as well as detriments of both low and high AL.

Callous-unemotional behaviors in early childhood: Genetic and environmental contributions to stability and change

Callous-unemotional (CU) behaviors demonstrate meaningful individual differences in early childhood, even in nonclinical samples with low mean levels of CU, but the factors underlying this variation have not been examined. This study investigated genetic and environmental contributions to individual differences and to sources of continuity and change in CU in toddler twins (145 monozygotic, 169 dizygotic) assessed at ages 2 and 3 years. CU, as assessed by the Child Behavior Checklist 1.5-5 (Achenbach & Rescorla, 2000), was moderately stable across age (r = .45, p < .0001). Longitudinal biometric analyses revealed genetic and nonshared environmental influences on CU at both ages, with no significant contribution from shared environmental factors. Stability from age 2 to 3 was due to genetic factors, whereas change was due to both genetic and nonshared environmental influences. This genetic and nonshared environmental change was substantial, suggesting malleability of CU in early childhood. Over 50% of the genetic influences and 100% of the nonshared environmental influences on CU at age 3 were independent of those that operated at age 2. Implications of novel sources of variance across age are discussed.

Measurement of obesity prevention in childcare settings: A systematic review of current instruments

OBJECTIVE

The incidence of childhood obesity is highest among children entering kindergarten. Overweight and obesity in early childhood track through adulthood. Programs increasingly target children in early life for obesity prevention. However, the published literature lacks a review on tools available for measuring behaviour and environmental level change in child care. The objective is to describe measurement tools currently in use in evaluating obesity-prevention in preschool-aged children.

METHODS

Literature searches were conducted in PubMed using the keywords "early childhood obesity," "early childhood measurement," "early childhood nutrition" and "early childhood physical activity." Inclusion criteria included a discussion of: (1) obesity prevention, risk assessment or treatment in children ages 1-5 years; and (2) measurement of nutrition or physical activity.

RESULTS

One hundred thirty-four publications were selected for analysis. Data on measurement tools, population and outcomes were abstracted into tables. Tables are divided by individual and environmental level measures and further divided into physical activity, diet and physical health outcomes. Recommendations are made for weighing advantages and disadvantages of tools.

CONCLUSION

Despite rising numbers of interventions targeting obesity-prevention and treatment in preschool-aged children, there is no consensus for which tools represent a gold standard or threshold of accuracy.

Frontal Electroencephalogram Asymmetry and Temperament Across Infancy and Early Childhood: An Exploration of Stability and Bidirectional Relations

The stability of frontal electroencephalogram (EEG) asymmetry, temperamental activity level and fear, as well as bidirectional relations between asymmetry and temperament across the first 4 years of life, were examined in a sample of 183 children. Children participated in annual laboratory visits through 48 months, providing EEG and maternal report of temperament. EEG asymmetry showed moderate stability between 10 and 24 months. Analyses revealed that more left asymmetry predicted later activity level across the first 3 years. Conversely, asymmetry did not predict fear. Rather, fear at 36 months predicted more right asymmetry at 48 months. Results highlight the need for additional longitudinal research of infants and children to increase understanding of bidirectional relations between EEG and temperament in typically developing populations.

The development of inhibitory control in early childhood: A twin study from 2-3 years

Parent- and lab-based observer ratings were employed to examine genetic and environmental influences on continuity and change in inhibitory control (IC) in over 300 twin-pairs assessed longitudinally at 2 and 3 years of age. Genetic influences accounted for approximately 60% of the variance in parent-rated IC at both ages. Although many of the same genetic effects on parent-rated IC were stable across age, there were also novel genetic effects that emerged at age 3 (i.e., genetic factors contributed to both continuity and change in parent ratings of IC). Observed IC displayed a different developmental pattern. Genetic influences were moderate at age 2 (38%) and nonsignificant at age 3 (6%). Change in observed IC across early childhood was due to shared and nonshared environmental factors. Findings indicate that it is important to consider the measurement of IC when interpreting developmental and etiological findings.

Difficult temperament and negative parenting in early childhood: a genetically informed cross-lagged analysis

A genetically informed longitudinal cross-lagged model was applied to twin data to explore etiological links between difficult temperament and negative parenting in early childhood. The sample comprised 313 monozygotic (MZ) and dizygotic (DZ) twin pairs. Difficult temperament and negative parenting were assessed at ages 2 and 3 using parent ratings. Both constructs were interrelated within and across age (rs .34-.47) and showed substantial stability (rs .65-.68). Difficult temperament and negative parenting were influenced by genetic and environmental factors at ages 2 and 3. The genetic and nonshared environmental correlations (rs .21-.76) at both ages suggest overlap at the level of etiology between the phenotypes. Significant bidirectional associations between difficult temperament and negative parenting were found. The cross-lagged association from difficult temperament at age 2 to negative parenting at age 3 and from negative parenting at age 2 and difficult temperament at age 3 were due to genetic, shared environmental, and nonshared environmental factors. Substantial novel genetic and nonshared environmental influences emerged at age 3 and suggest change in the etiology of these constructs over time.

The importance of genotype-by-age interactions for the development of repeatable behavior and correlated behaviors over lifetime

Behaviors are highly plastic and one aspect of this plasticity is behavioral changes over age. The presence of age-related plasticity in behavior opens up the possibility of between-individual variation in age-related plasticity (Individual-Age interaction, IxA) and genotype-age interaction (GxA). We outline the available approaches for quantifying GxA. We underline that knowledge of GxA for behaviors is an important step in reaching and understanding of the evolution of plasticity in behavior over lifetime. In particular, the heritability (repeatability) and/or the rank order of behavior across individuals are predicted to change across ages in presence of GxA. We draw on the theory of reaction norms to illustrate that GxA, when present, is likely to lead to developmental changes in the magnitude and possibly sign of the genetic correlation between behaviors (behavioral syndrome). We present an overview of the literature on changes in the ranking of individuals’ behavior across ages, and in the correlation between behaviors. Although all studies were carried out on the phenotypic level, they overall suggest clear scope for increased study of GxA as a process explaining age-related plasticity in behaviors. Lastly, we throughout emphasize that many of the approaches and underlying theory of GxA is applicable to the study of IxA, which is informative as it presents the upper limit of GxA, but is also a more attainable target of study in many systems. Empirical work aimed at understanding IxA and GxA in behavior is needed in order to understand whether patterns predicted by theory on plasticity indeed occur for age-related plasticity of behavior.

How else can we study sex differences in early infancy?

This paper revisits group difference and individual variability in birth weight, head size, Apgar score, and motor performance in neonatal and 8-month-old males and females using a large existing data set. The goal is primarily theoretical--to reframe existing analyses with an eye toward designing and executing more predictive analyses in the future. 3D graphing to visualize both the areas of overlap and regions of disparity between boys and girls has been used. A two-step cluster analysis of boys and girls together revealed three clusters. One was almost equally divided between boys and girls, but a second was highly enriched for boys and the third highly skewed toward girls. The relationship between cluster membership and Bayley motor scores at 8 months tested the hypothesis that initial differences that have no sex-related behavioral content might start processes that produce later sex-related differences. Initially, parental belief systems may be less important than infant care patterns evoked by basic size and health characteristics, even though later parental behaviors assume a decidedly gendered pattern.

Are children's activity levels determined by their genes or environment? A systematic review of twin studies

CONTEXT

The importance of physical activity to paediatric health warrants investigation into its determinants. Objective measurement allows a robust examination of genetic and environmental influences on physical activity.

OBJECTIVE

To systematically review the evidence on the extent of genetic and environmental influence on children's objectively-measured activity levels from twin studies.

DATA SOURCES AND SEARCH TERMS

Medline, EMBASE, PsycINFO, Health and Psychosocial Instruments and all Ovid Databases. Search terms: "accelerometer" OR "actometer" OR "motion sensor" OR "heart rate monitor" OR "physical activity energy expenditure" AND "twin". Limited to Human, English language and children (0-18 years).

RESULTS

Seven sets of analyses were included in the review. Six analyses examined children's daily-life activity and found that the shared environment had a strong influence on activity levels (weighted mean 60%), with a smaller contribution from genetic factors (weighted mean 21%). Two analyses examined short-term, self-directed activity in a standard environment and found a smaller shared environment effect (weighted mean 25%) and a larger genetic estimate (weighted mean 45%).

CONCLUSIONS

Although genetic influences may be expressed when children have brief opportunities for autonomous activity, activity levels in daily-life are predominantly explained by environmental factors. Future research should aim to identify key environmental drivers of childhood activity.

Infant temperament: stability by age, gender, birth order, term status, and socioeconomic status

Two complementary studies focused on stability of infant temperament across the 1st year and considered infant age, gender, birth order, term status, and socioeconomic status (SES) as moderators. Study 1 consisted of 73 mothers of firstborn term girls and boys queried at 2, 5, and 13 months of age. Study 2 consisted of 335 mothers of infants of different gender, birth order, term status, and SES queried at 6 and 12 months. Consistent positive and negative affectivity factors emerged at all time points across both studies. Infant temperament proved stable and robust across gender, birth order, term status, and SES. Stability coefficients for temperament factors and scales were medium to large for shorter (< 9 months) interassessment intervals and small to medium for longer (> 10 months) intervals.

Emerging Trends in Behavioral Genetic Studies of Child Temperament

In this article, we describe three emerging trends in the application of behavioral genetic methods to the study of temperament. The trends-using multiple methods to assess temperament, considering contextual influences on temperament, and evaluating the structure of temperament-have been well studied in the phenotypic literature, but adding a behavioral genetic perspective can enrich our understanding of temperament. We review recent behavioral genetic research in each of these areas and discuss its implications.

Genetic and environmental continuity in personality development: a meta-analysis

The longitudinal stability of personality is low in childhood but increases substantially into adulthood. Theoretical explanations for this trend differ in the emphasis placed on intrinsic maturation and socializing influences. To what extent does the increasing stability of personality result from the continuity and crystallization of genetically influenced individual differences, and to what extent does the increasing stability of life experiences explain increases in personality trait stability? Behavioral genetic studies, which decompose longitudinal stability into sources associated with genetic and environmental variation, can help to address this question. We aggregated effect sizes from 24 longitudinal behavioral genetic studies containing information on a total of 21,057 sibling pairs from 6 types that varied in terms of genetic relatedness and ranged in age from infancy to old age. A combination of linear and nonlinear meta-analytic regression models were used to evaluate age trends in levels of heritability and environmentality, stabilities of genetic and environmental effects, and the contributions of genetic and environmental effects to overall phenotypic stability. Both the genetic and environmental influences on personality increase in stability with age. The contribution of genetic effects to phenotypic stability is moderate in magnitude and relatively constant with age, in part because of small-to-moderate decreases in the heritability of personality over child development that offset increases in genetic stability. In contrast, the contribution of environmental effects to phenotypic stability increases from near zero in early childhood to moderate in adulthood. The life-span trend of increasing phenotypic stability, therefore, predominantly results from environmental mechanisms.

The Boston University Twin Project (BUTP)

The Boston University Twin Project (BUTP) is a multi-method, multi-situation, longitudinal study of early child temperament and related behaviors. The first phase of this project focused primarily on activity level and comprised over 300 twin pairs assessed in the home and lab at ages 2 and 3. Subject recruitment, sample characteristics, and study procedures are described. A second phase broadens our focus to the development of multiple temperament dimensions and developmental outcomes in a new cohort of 300 twin pairs to be assessed at 3, 4, and 5 years of age. Recruitment is currently underway.