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According to the failure model (Patterson & Capaldi, 1990), peer rejection is the intermediary link between problem behaviors and internalizing symptoms. The present study tested the model with 464 monozygotic and same-sex dizygotic twin pairs (234 female, 230 male dyads). Teacher-reported reactive aggression and internalizing symptoms, and peer-reported peer rejection were collected at ages 6, 7, and 10 (from 2001 to 2008). Support for the failure model emerged in conventional non-genetically controlled analyses, but not twin-difference score analyses (which remove shared environmental and genetic contributions). Univariate biometric models attributed minimal variance in failure model variables to shared environmental factors, suggesting that genetic factors play an important unacknowledged role in developmental pathways historically ascribed to nonshared experiences in the failure model., (© 2023 The Authors. Child Development © 2023 Society for Research in Child Development.)

This study examines the link between behavior in kindergarten and adult-life welfare receipt. Teacher-rated behavioral assessments were obtained for inattention, hyperactivity, aggression-opposition, anxiety, and prosociality when children ( n =2960) were aged 5-6 years and linked to their tax return records from age 18-35 years. We used group-based based trajectory modeling to identify distinct trajectories of welfare receipt and multinomial logistic regression models to examine the association between behaviors and trajectory group membership. The child's sex, IQ, and family background were adjusted for. Four trajectories of welfare receipt were identified: low ( n = 2,390, 80.7%), declining ( n = 260, 8.8%), rising ( n = 150, 5.2%), and chronic ( n = 160, 5.4%). Relative to the low trajectory, inattention and aggression-opposition at age 6 years were associated with increased risk of following a declining, rising, and chronic trajectory of welfare receipt, independent of hyperactivity and anxiety. Prosocial behaviors were independently associated with a lower risk of following a chronic trajectory. This study shows that kindergarten children exhibiting high inattention and aggression-opposition and low prosocial behaviors may be at increased risk of long-term welfare receipt in adulthood. The implications for early screening, monitoring, and prevention are discussed.

Aggressive behavior is generally detrimental to children's friendships, both in terms of having friends and in terms of keeping friends. Despite this general tendency, many aggressive children have friends and some of these friendships are stable. We examined the moderating role of preference norms in the classroom and child's sex in the association between children's physical and relational aggression and their friendship experiences. A total of 1135 children (M = 10.24 years, SD = 1.01) in Grades 4 to 6 completed a peer nomination inventory in the Fall (T1) and Spring (T2) of the same school year. Norms were operationalized as the class- and sex-specific correlation between physical or relational aggression and social preference. Norms moderated associations between each form of aggression and number of friends. At T1, physical and relational aggression were concurrently associated with having more friends when norms favored this behavior and with fewer friends when norms were unfavorable. The latter effect was especially pronounced in girls. Over time, youth lost friends when norms favored physical aggression and gained friends when norms favored relational aggression. T1 friends' physical and relational aggression were strong predictors of new friends' aggressive behavior, suggesting that friends provide a type of norm more significant to new friend selection than norms of the peer group and individual aggressive behavior. Overall, our results suggest that physical and relational aggression are not necessarily detrimental to children's friendship experiences and may even be beneficial in specific social contexts., (© 2021 Wiley Periodicals LLC.)

This study examined bidirectional links between teachers' disciplinary practices (punitive and educational), students' peer status in class (acceptance and rejection), and students' aggressive behaviors. A sample comprising 1,038 students (mean age = 5.43 years) was assessed with the same instruments in the fall and spring of one kindergarten year. Teachers reported the disciplinary practices they used with each student in their class. Aggression, peer rejection, and peer acceptance were measured by peer sociometric nomination. Autoregressive cross-lagged modeling was used to test bidirectional associations. The results showed reciprocal links between punitive disciplinary practices, peer rejection, and students' aggressive behaviors. More specifically, punitive discipline at kindergarten start predicted greater peer rejection and higher levels of aggressive behaviors at year end. Students' aggressive behaviors and peer rejection at year start predicted greater use of punitive practice at year end. Educational discipline did not contribute to a change in students' peer status and students' aggressive behaviors.

Background: Population-based and family studies showed that impulsive-aggression predicts suicidality; however, the underlying etiological nature of this association is poorly understood. The objective was to determine the contribution of genes and environment to the association between childhood impulsive-aggression and serious suicidal ideation/attempt in young adulthood., Methods: N = 862 twins (435 families) from the Quebec Newborn Twin Study were followed up from birth to 20 years. Repeated measures of teacher-assessed impulsive-aggression were modeled using a genetically informed latent growth model including intercept and slope parameters reflecting individual differences in the baseline level (age 6 years) and in the change (increase/decrease) of impulsive-aggression during childhood (6 to 12 years), respectively. Lifetime suicidality (serious suicidal ideation/attempt) was self-reported at 20 years. Associations of impulsive-aggression intercept and slope with suicidality were decomposed into additive genetic (A) and unique environmental (E) components., Results: Additive genetic factors accounted for an important part of individual differences in impulsive-aggression intercept (A = 90%, E = 10%) and slope (A = 65%, E = 35%). Genetic (50%) and unique environmental (50%) factors equally contributed to suicidality. We found that 38% of the genetic factors accounting for suicidality were shared with those underlying impulsive-aggression slope, whereas 40% of the environmental factors accounting for suicidality were shared with those associated with impulsive-aggression intercept. The genetic correlation between impulsive-aggression slope and suicidality was 0.60, p = .027., Conclusions: Genetic and unique environmental factors underlying suicidality significantly overlap with those underlying childhood impulsive-aggression. Future studies should identify putative genetic and environmental factors to inform prevention., (© 2019 Association for Child and Adolescent Mental Health.)

Resource Control Theory (Hawley, 1999) posits a group of bistrategic popular youth who attain status through coercive strategies while mitigating fallout via prosociality. This study identifies and distinguishes this bistrategic popular group from other popularity types, tracing the adjustment correlates of each. Adolescent participants (288 girls, 280 boys; M age  = 12.50 years) completed peer nominations in the Fall and Spring of the seventh and eighth grades. Longitudinal latent profile analyses classified adolescents into groups based on physical and relational aggression, prosocial behavior, and popularity. Distinct bistrategic, aggressive, and prosocial popularity types emerged. Bistrategic popular adolescents had the highest popularity and above average aggression and prosocial behavior; they were viewed by peers as disruptive and angry but were otherwise well-adjusted., (© 2019 The Authors. Child Development © 2019 Society for Research in Child Development, Inc.)

Background: Child-care services during early childhood provide opportunities for social interactions that may facilitate children's learning of acceptable social behaviors. Furthermore, they may reduce exposure to family adversity for some children. The aim of this study was to determine whether intensity of exposure to child-care services prior to age 5 years has a beneficial effect on disruptive behavior problems during adolescence, and whether the effect is more pronounced for children from low socioeconomic families., Methods: N = 1,588 participants from the Québec Longitudinal Study of Child Development were assessed 14 times from 5 months to 17 years. Intensity of child-care exposure was measured from 5 months to 5 years of age. Main outcomes were self-reported physical aggression and opposition from age 12 to 17 years. Family socioeconomic status (SES) was measured at 5 months. Factors explaining differences in child-care use were controlled using propensity score weights (PSW)., Results: Children exposed to moderate-intensity child-care services (part-time child-care services before 1½ years and full time afterward) reported lower levels of physical aggression (d = -.11, p = .056) and opposition (d = -.14, p = .029) during adolescence compared to children exposed to low-intensity child-care services. A significant child care by SES interaction (p = .017) for physical aggression indicated that the moderate-intensity child-care effect was specific to children from low SES families (d = -.36, p = .002). No interaction with socioeconomic status was found for opposition., Conclusions: Moderate-intensity child-care services from infancy to school entry may prevent disruptive behavior during adolescence, especially for disadvantaged children., (© 2019 Association for Child and Adolescent Mental Health.)

Importance: Specifying the association between childhood behaviors and adult earnings can inform the development of screening tools and preventive interventions to enhance social integration and economic participation., Objective: To test the association between behaviors at age 6 years and employment earnings at age 33 to 35 years., Design, Setting, and Participants: This study obtained data from the Quebec Longitudinal Study of Kindergarten Children, a population-based sample of boys and girls (n = 3020) born in 1980 or 1981 in Quebec, Canada, and followed up from January 1, 1985, to December 31, 2015. The data included behavioral ratings by kindergarten teachers when the children were aged 5 or 6 years and 2013 to 2015 government tax returns of those same participants at age 33 to 35 years. Data were analyzed from September 2017 to December 2018., Main Outcomes and Measures: Mixed-effects linear regression models were used to test the associations between teacher-rated inattention, hyperactivity, aggression, opposition, anxiety, and prosociality at age 6 years and reported annual earnings on income tax returns at age 33 to 35 years. Participant IQ and family adversity were adjusted for in the analysis., Results: The study included 2850 participants, with a mean (SD) age of 35.9 (0.29) years, of whom 1470 (51.6%) were male and 2740 (96.2%) were white. The mean (SD) personal earnings at follow-up were US $33 300 ($27 500) for men and $19 400 ($15 200) for women. A 1-unit increase in inattention score at age 6 years (males mean [SD], 2.47 [2.42] vs females mean [SD], 1.67 [2.07]) was associated with a decrease in annual earnings of $1271.49 (95% CI, -1908.67 to -634.30) for male participants and $924.25 (95% CI, -1424.44 to -425.46) for female participants. A combined aggression-opposition score (males mean [SD] 2.22 [2.52] vs females mean [SD], 1.05 [1.73]) was associated with a reduction in earnings of $699.83 (95% CI, -1262.49 to -137.17) for males only, albeit with an effect size roughly half that of inattention. A 1-unit increase in prosociality score (males mean [SD], 6.12 [4.30] vs females mean [SD], 7.90 [4.56]) was associated with an increase in earnings of $476.75 (95% CI, 181.53-771.96) for male participants only. A 1-SD reduction in inattention score at age 6 years would theoretically restore $3077 in annual earnings for male participants and $1915 for female participants., Conclusions and Relevance: In this large population-based sample of kindergarten children, behavioral ratings at 5-6 years were associated with employment earnings 3 decades later, independent of a person's IQ and family background. Inattention and aggression-opposition were associated with lower annual employment earnings, and prosociality with higher earnings but only among male participants; inattention was the only behavioral predictor of income among girls. Early monitoring and support for children demonstrating high inattention and for boys exhibiting high aggression-opposition and low prosocial behaviors could have long-term advantages for those individuals and society.

Importance: This study used multitrajectory modeling to identify distinct trajectories of physical aggression from ages 1.5 to 13 years for boys and girls., Objectives: To trace the development of boys' and girls' physical aggression problems from infancy to adolescence using mother ratings, teacher ratings, and self-ratings and to identify early family predictors of children on the high physical aggression trajectories., Design, Setting, and Participants: This cohort study used data from the Quebec Longitudinal Study of Child Development (QLSCD), a study of a representative, population-based sample of 2223 infants born in 1997 and 1998 in the Canadian province of Quebec. The dates of analysis were January 2017 to January 2018., Main Outcomes and Measures: Trained research assistants conducted 7 interviews (at child ages 1.5, 2.5, 3.5, 4.5, 5, 6, and 8 years) with the person most knowledgeable about the child (mothers in 99.6% [2214 of 2223] of cases). Teachers assessed the child's behavior at ages 6, 7, 8, 10, 12, and 13 years. Self-reports of behavior problems were obtained from the child at ages 10, 12, and 13 years., Results: The sample included 2223 participants, 51.2% of whom were boys and 91.2% of whom were of white race/ethnicity. The mean response rate for mother ratings of physical aggression during the first 8 years of life was 80.9% (range, 65.1%-91.7%). For teacher ratings of physical aggression from ages 6 to 13 years, the mean response rate was 45.7% (range, 35.4%-56.9%), while the mean response rate of physical aggression assessment from self-ratings between ages 10 and 13 years was 57.9% (range, 55.2%-60.5%). Attrition was higher among families with low socioeconomic status and single-parent families, as well as among young mothers and mothers who were not fluent in French or English. A statistical analysis to examine the consequences of attrition was included. For boys and girls, the frequency of physical aggressions increased from age 1.5 years (2039 [91.7%]) to age 3.5 years (1941 [87.3%]) and then substantially decreased until age 13 years (1228 [55.2%]). Three distinct developmental trajectories of physical aggression were observed for girls and 5 for boys. Most family characteristics measured at 5 months after the child's birth were associated with a high physical aggression trajectory for boys and girls., Conclusions and Relevance: Family characteristics at 5 months after the child's birth could be used to target preschool interventions aimed at preventing the development of boys' and girls' chronic physical aggression problems.

Epigenetic processes that regulate gene expression, such as DNA methylation (DNAm), have been linked to individual differences in physical aggression. Yet, it is currently unclear whether: (a) DNAm patterns in humans associate with physical aggression independently of other co-occurring psychiatric and behavioral symptoms; (b) whether these patterns are observable across multiple tissues; and (c) whether they may function as a causal versus noncausal biomarker of physical aggression. Here, we used a multisample, cross-tissue design to address these questions. First, we examined genome-wide DNAm patterns (buccal swabs; Illumina 450k) associated with engagement in physical fights in a sample of high-risk youth (n = 119; age = 16-24 years; 53% female). We identified one differentially methylated region in DRD4, which survived genome-wide correction, associated with physical aggression above and beyond co-occurring symptomatology (e.g., ADHD, substance use), and showed strong cross-tissue concordance with both blood and brain. Second, we found that DNAm sites within this region were also differentially methylated in an independent sample of young adults, between individuals with a history of chronic-high versus low physical aggression (peripheral T cells; ages 26-28). Finally, we ran a Mendelian randomization analysis using GWAS data from the EAGLE consortium to test for a causal association of DRD4 methylation with physical aggression. Only one genetic instrument was eligible for the analysis, and results provided no evidence for a causal association. Overall, our findings lend support for peripheral DRD4 methylation as a potential biomarker of physically aggressive behavior, with no evidence yet of a causal relationship., (© 2018 Wiley Periodicals, Inc.)

This study examined the moderating role of classroom injunctive norms salience regarding social withdrawal and regarding aggression in the longitudinal association between these behaviors and peer victimization. A total of 1,769 fourth through sixth graders (895 girls, M = 10.25 years, SD = 1.03) from 23 schools (67 classrooms) completed a peer nomination inventory in the fall (T1) and spring (T2) of the same academic year. Participants circled the name of each student who fit the description provided for social withdrawal, aggression, and peer victimization at T1 and T2. The salience of injunctive norms was sex-specific and operationalized by the extent to which children displaying the behavior were socially rewarded or sanctioned by their classmates. Generalized estimation equations (GEE) showed that the association between social withdrawal at T1 and peer victimization at T2 was moderated by injunctive norms. Social withdrawal at T1 was positively associated with peer victimization at T2 in classrooms where injunctive norms for this behavior were salient and unfavorable, as well as in classrooms where injunctive norms for aggression were salient and favorable, albeit for girls only. The association between aggression at T1 and peer victimization at T2 was also moderated by the injunctive norms regarding this behavior. Aggressive children were less likely to be victimized in classrooms where this behavior was rewarded. These results support bullying interventions that target factors related to the larger peer context, including social norms. (PsycINFO Database Record, ((c) 2018 APA, all rights reserved).)

Past studies have identified various risk and protective factors for problem gambling (PG). However, no study has examined the interplay between these factors using a combination of person-centered and variable-centered approaches embedded within a longitudinal design. The present study aimed to (a) identify distinct profiles in early adolescence based on a set of risk factors commonly associated with PG (impulsivity, depression, anxiety, drug-alcohol use, aggressiveness, and antisociality), (b) explore the difference in reported gambling problems between these profiles during midadolescence and early adulthood, and (c) identify family- and peer-related variables that could operate as protective or compensatory factors in this context. Two samples were used: (a) a population sample (N = 1,033) living in low socioeconomic-status neighborhoods and (b) a population sample (N = 3,017) representative of students attending Quebec schools. Latent profile analyses were conducted to identify at-risk profiles based on individual risk factors measured at age 12 years. Negative binomial regression models were estimated to compare profiles in terms of their reported gambling problems at ages 16 and 23. Finally, family- and peer-related variables measured at age 14 were included to test their protective or compensatory role with respect to the link between at-risk profiles and gambling problems. Four profiles were identified: well-adjusted, internalizing, externalizing, and comorbid. Compared to the well-adjusted profile, the externalizing and comorbid profiles reported more gambling problems at ages 16 and 23, but the internalizing profile did not differ significantly. Various protective and compensatory factors emerged for each profile at both time points. (PsycINFO Database Record, ((c) 2018 APA, all rights reserved).)

This review describes a bio-psycho-social approach to understanding and preventing the development of chronic physical aggression. The debate on the developmental origins of aggression has historically opposed genetic and environmental mechanisms. Recent studies have shown that the frequency of physical aggression peaks in early childhood and then decreases until old age. Molecular genetic studies and twin studies have confirmed important genetic influences. However, recent epigenetic studies have highlighted the important role of environments in gene expression and brain development. These studies suggest that interrelated bio-psycho-social channels involved in the development of chronic physical aggression are generally the product of an intergenerational transmission process occurring through assortative mating, genetic inheritance, and the inheritance of physical and social environmental conditions that handicap brain functioning and support the use of physical aggression to solve problems. Given these intergenerational mechanisms and physical aggression onset in infancy, it appears clear that preventive interventions should start early in pregnancy, at the latest.

Background: Few studies are grounded in a developmental framework to study proactive and reactive aggression. Furthermore, although distinctive correlates, predictors and outcomes have been highlighted, proactive and reactive aggression are substantially correlated. To our knowledge, no empirical study has examined the communality of genetic and environmental underpinning of the development of both subtypes of aggression. The current study investigated the communality and specificity of genetic-environmental factors related to heterogeneity in proactive and reactive aggression's development throughout childhood., Methods: Participants were 223 monozygotic and 332 dizygotic pairs. Teacher reports of aggression were obtained at 6, 7, 9, 10 and 12 years of age. Joint development of both phenotypes were analyzed through a multivariate latent growth curve model. Set point, differentiation, and genetic maturation/environmental modulation hypotheses were tested using a biometric decomposition of intercepts and slopes., Results: Common genetic factors accounted for 64% of the total variation of proactive and reactive aggression's intercepts. Two other sets of uncorrelated genetic factors accounted for reactive aggression's intercept (17%) on the one hand, and for proactive (43%) and reactive (13%) aggression's slopes on the other. Common shared environmental factors were associated with proactive aggression's intercept (21%) and slope (26%) and uncorrelated shared environmental factors were also associated with reactive aggression's slope (14%). Common nonshared environmental factors explained most of the remaining variability of proactive and reactive aggression slopes., Conclusions: A genetic differentiation hypothesis common to both phenotypes was supported by common genetic factors associated with the developmental heterogeneity of proactive and reactive aggression in childhood. A genetic maturation hypothesis common to both phenotypes, albeit stronger for proactive aggression, was supported by common genetic factors associated with proactive and reactive aggression slopes. A shared environment set point hypothesis for proactive aggression was supported by shared environmental factors associated with proactive aggression baseline and slope. Although there are many common features to proactive and reactive aggression, the current research underscores the advantages of differentiating them when studying aggression.

Using a sample of 767 children (403 girls, 364 boys), this study aimed to (a) identify groups with distinct trajectories of peer victimization over a 6-year period from primary school through the transition to secondary school, and (b) examine the associated personal (i.e., aggression or internalizing problems) and familial (family status, socioeconomic status, the parent-child relationship) predictors. Peer victimization was assessed via self-reports from Grades 4 through 9 (ages 10 through 15 years), aggression and internalizing problems were assessed in Grade 4 via peer nominations, and the parent-child relationship was assessed in Grade 7 (i.e., right after the transition to secondary school) via parent-reports. Growth Mixture modeling revealed 1 group (62%) who experienced little victimization in primary school and even less in secondary school, another group (31%) who was victimized in primary but not or much less in secondary school, and a third group (7%) who was chronically victimized in both school contexts. Boys were more likely than girls to follow any elevated victimization trajectory. Chronic victimization across primary and secondary school was predicted by nonintact family status and a combination of both internalizing problems and aggression compared with nonvictimized youth. In contrast, transitory victimization during primary but not in secondary school was predicted by aggression, but not internalizing problems. Support as well as conflict in the parent-child relationship also showed significant, albeit distinct associations with the different peer victimization trajectories. (PsycINFO Database Record, ((c) 2016 APA, all rights reserved).)

The present study examined sibling influence over reactive and proactive aggression in a sample of 452 same-sex twins (113 male dyads, 113 female dyads). Between and within siblings influence processes were examined as a function of relative levels of parental coercion and hostility to test the hypothesis that aggression contagion between twins occurs only among dyads who experience parental coerciveness. Teacher reports of reactive and proactive aggression were collected for each twin in kindergarten (M = 6.04 years; SD = 0.27) and in first grade (M = 7.08 years; SD = 0.27). Families were divided into relatively low, average, and relatively high parental coercion-hostility groups on the basis of maternal reports collected when the children were 5 years old. In families with relatively high levels of parental coercion-hostility, there was evidence of between-sibling influence, such that one twin's reactive aggression at age 6 predicted increases in the other twin's reactive aggression from ages 6 to 7, and one twin's proactive aggression at age 6 predicted increases in the other twin's proactive aggression from ages 6 to 7. There was also evidence of within-sibling influence such that a child's level of reactive aggression at age 6 predicted increases in the same child's proactive aggression at age 7, regardless of parental coercion-hostility. The findings provide new information about the etiology of reactive and proactive aggression and individual differences in their developmental interplay., (© 2015 Wiley Periodicals, Inc.)

Numerous studies have shown that aggressive and non-aggressive antisocial behaviors are important precursors of later adjustment problems. There is also strong empirical evidence that both types of antisocial behavior are partially influenced by genetic factors. However, despite its important theoretical and practical implications, no study has examined the question whether environmental factors differentially moderate the expression of genetic influences on the two types of antisocial behavior. Using a genetically informed design based on 266 monozygotic and dizygotic twin pairs, this study examined whether the expression of genetic risk for aggressive and non-aggressive antisocial behavior varies depending on the peer group's injunctive norms (i.e., the degree of acceptability) of each type of antisocial behavior. Self-reported aggressive and non-aggressive antisocial behavior and classroom-based sociometric nominations were collected when participants were 10 years old. Multivariate genetic analyses revealed some common genetic factors influencing both types of antisocial behavior (i.e., general antisocial behavior) as well as genetic influences specific to non-aggressive antisocial behavior. However, genetic influences on general antisocial behavior, as well as specific genetic influences on non-aggressive antisocial behavior, vary depending on the injunctive classroom norms regarding these behaviors. These findings speak to the power of peer group norms in shaping aggressive and non-aggressive antisocial behavior. They also contribute further to understanding the distinctive development of both types of antisocial behavior. Finally, they may have important implications for prevention purposes.

Using a genetically informed design based on 197 Monozygotic and Dizygotic twin pairs assessed in grade 4, this study examined 1) whether, in line with a gene-environment correlation (rGE), a genetic disposition for physical aggression or relational aggression puts children at risk of being victimized by their classmates, and 2) whether this rGE is moderated by classroom injunctive norm salience in regard to physical or relational aggression. Physical aggression and relational aggression, as well as injunctive classroom norm salience in regard to these behaviors, were measured via peer nominations. Peer victimization was measured via self-reports. Multi-Level Mixed modeling revealed that children with a genetic disposition for either aggressive behavior are at higher risk of being victimized by their peers only when classroom norms are unfavourable toward such behaviors. However, when classroom injunctive norms favor aggressive behaviors, a genetic disposition for physical or relational aggression may actually protect children against peer victimization. These results lend further support to the notion that bullying interventions must include the larger peer context instead of a sole focus on victims and bullies.

Several authors consider high and frequent conflicts between friends during childhood as a serious risk for subsequent conduct problems such as generalized physical aggression toward others (e.g., Kupersmidt, Burchinal, & Patterson, 1995; Sebanc, 2003). Although it seems logical to assume that friendship conflict could have some negative consequences on children's behaviors, some scholars have suggested that a certain amount of conflict between friends may actually promote social adjustment (e.g., Laursen & Pursell, 2009). The aim of this study was to investigate the role of friendship conflict in regard to the development of generalized physical aggression toward others in the early school years (i.e., from kindergarten to Grade 1), as well as the moderating role of relational (i.e., shared positive affect and dyadic conflict resolution skills) and personal (i.e., children's sex and genetic liability for aggression) characteristics in this context. The sample included 745 twins assessed through teacher, peer, child, and friend ratings in kindergarten and Grade 1. Friendship conflict in kindergarten was linearly related to an increase in boys' but not girls' generalized physical aggression. However, shared positive affect and conflict resolution skills mitigated the prospective associations between friendship conflict and generalized physical aggression. These results were independent of children's sex, genetic risk for physical aggression, and initial levels of generalized physical aggression in kindergarten. Fostering a positive relationship between friends at school entry may buffer against the risk associated with experiencing friendship conflict., (PsycINFO Database Record (c) 2014 APA, all rights reserved.)

Background: Chronic physical aggression (CPA) is characterized by frequent use of physical aggression from early childhood to adolescence. Observed in approximately 5% of males, CPA is associated with early childhood adverse environments and long-term negative consequences. Alterations in DNA methylation, a covalent modification of DNA that regulates genome function, have been associated with early childhood adversity., Aims: To test the hypothesis that a trajectory of chronic physical aggression during childhood is associated with a distinct DNA methylation profile during adulthood., Methods: We analyzed genome-wide promoter DNA methylation profiles of T cells from two groups of adult males assessed annually for frequency of physical aggression between 6 and 15 years of age: a group with CPA and a control group. Methylation profiles covering the promoter regions of 20 000 genes and 400 microRNAs were generated using MeDIP followed by hybridization to microarrays., Results: In total, 448 distinct gene promoters were differentially methylated in CPA. Functionally, many of these genes have previously been shown to play a role in aggression and were enriched in biological pathways affected by behavior. Their locations in the genome tended to form clusters spanning millions of bases in the genome., Conclusions: This study provides evidence of clustered and genome-wide variation in promoter DNA methylation in young adults that associates with a history of chronic physical aggression from 6 to 15 years of age. However, longitudinal studies of methylation during early childhood will be necessary to determine if and how this methylation variation in T cells DNA plays a role in early development of chronic physical aggression.

Background: High frequency of physical aggression is the central feature of severe conduct disorder and is associated with a wide range of social, mental and physical health problems. We have previously tested the hypothesis that differential DNA methylation signatures in peripheral T cells are associated with a chronic aggression trajectory in males. Despite the fact that sex differences appear to play a pivotal role in determining the development, magnitude and frequency of aggression, most of previous studies focused on males, so little is known about female chronic physical aggression. We therefore tested here whether or not there is a signature of physical aggression in female DNA methylation and, if there is, how it relates to the signature observed in males., Methodology/principal Findings: Methylation profiles were created using the method of methylated DNA immunoprecipitation (MeDIP) followed by microarray hybridization and statistical and bioinformatic analyses on T cell DNA obtained from adult women who were found to be on a chronic physical aggression trajectory (CPA) between 6 and 12 years of age compared to women who followed a normal physical aggression trajectory. We confirmed the existence of a well-defined, genome-wide signature of DNA methylation associated with chronic physical aggression in the peripheral T cells of adult females that includes many of the genes similarly associated with physical aggression in the same cell types of adult males., Conclusions: This study in a small number of women presents preliminary evidence for a genome-wide variation in promoter DNA methylation that associates with CPA in women that warrant larger studies for further verification. A significant proportion of these associations were previously observed in men with CPA supporting the hypothesis that the epigenetic signature of early life aggression in females is composed of a component specific to females and another common to both males and females.

Background: Animal and human studies suggest that inflammation is associated with behavioral disorders including aggression. We have recently shown that physical aggression of boys during childhood is strongly associated with reduced plasma levels of cytokines IL-1α, IL-4, IL-6, IL-8 and IL-10, later in early adulthood. This study tests the hypothesis that there is an association between differential DNA methylation regions in cytokine genes in T cells and monocytes DNA in adult subjects and a trajectory of physical aggression from childhood to adolescence., Methodology/principal Findings: We compared the methylation profiles of the entire genomic loci encompassing the IL-1α, IL-6, IL-4, IL-10 and IL-8 and three of their regulatory transcription factors (TF) NFkB1, NFAT5 and STAT6 genes in adult males on a chronic physical aggression trajectory (CPA) and males with the same background who followed a normal physical aggression trajectory (control group) from childhood to adolescence. We used the method of methylated DNA immunoprecipitation with comprehensive cytokine gene loci and TF loci microarray hybridization, statistical analysis and false discovery rate correction. We found differentially methylated regions to associate with CPA in both the cytokine loci as well as in their transcription factors loci analyzed. Some of these differentially methylated regions were located in known regulatory regions whereas others, to our knowledge, were previously unknown as regulatory areas. However, using the ENCODE database, we were able to identify key regulatory elements in many of these regions that indicate that they might be involved in the regulation of cytokine expression., Conclusions: We provide here the first evidence for an association between differential DNA methylation in cytokines and their regulators in T cells and monocytes and male physical aggression.

Background: An increasing number of animal and human studies are indicating that inflammation is associated with behavioral disorders including aggression. This study investigates the association between chronic physical aggression during childhood and plasma cytokine levels in early adulthood., Methodology/principal Findings: Two longitudinal studies were used to select males on a chronic physical aggression trajectory from childhood to adolescence (n = 7) and a control group from the same background (n = 25). Physical aggression was assessed yearly by teachers from childhood to adolescence and plasma levels of 10 inflammatory cytokines were assessed at age 26 and 28 years. Compared to the control group, males on a chronic physical aggression trajectory from childhood to adolescence had consistently lower plasma levels of five cytokines: lower pro-inflammatory interleukins IL-1α (T(28.7) = 3.48, P = 0.002) and IL-6 (T(26.9) = 3.76, P = 0.001), lower anti-inflammatory interleukin IL-4 (T(27.1) = 4.91, P = 0.00004) and IL-10 (T(29.8) = 2.84, P = 0.008) and lower chemokine IL-8 (T(26) = 3.69, P = 0.001). The plasma levels of four cytokines accurately predicted aggressive and control group membership for all subjects., Conclusions/significance: Physical aggression of boys during childhood is a strong predictor of reduced plasma levels of cytokines in early adulthood. The causal and physiological relations underlying this association should be further investigated since animal data suggest that some cytokines such as IL-6 and IL-1β play a causal role in aggression.

Background: Research shows that children with Attention Deficit/Hyperactivity Disorder are at elevated risk of criminality. However, several issues still need to be addressed in order to verify whether hyperactivity in itself plays a role in the prediction of criminality. In particular, co-occurrence with other behaviors as well as the internal heterogeneity in ADHD symptoms (hyperactivity and inattention) should be taken into account. The aim of this study was to assess the unique and interactive contributions of hyperactivity to the development of criminality, whilst considering inattention, physical aggression and family adversity., Methodology/principal Findings: We monitored the development of a population-based sample of kindergarten children (N = 2,741). Hyperactivity, inattention, and physical aggression were assessed annually between the ages of 6 and 12 years by mothers and teachers. Information on the presence, the age at first charge and the type of criminal charge was obtained from official records when the participants were aged 25 years. We used survival analysis models to predict the development of criminality in adolescence and adulthood: high childhood hyperactivity was highly predictive when bivariate analyses were used; however, with multivariate analyses, high hyperactivity was only marginally significant (Hazard Ratio: 1.38; 95% CI: 0.94-2.02). Sensitivity analyses revealed that hyperactivity was not a consistent predictor. High physical aggression was strongly predictive (Hazard Ratio: 3.44; 95% CI: 2.43-4.87) and its role was consistent in sensitivity analyses and for different types of crime. Inattention was not predictive of later criminality., Conclusions/significance: Although the contribution of childhood hyperactivity to criminality may be detected in large samples using multi-informant longitudinal designs, our results show that it is not a strong predictor of later criminality. Crime prevention should instead target children with the highest levels of childhood physical aggression and family adversity.

Objective: To examine associations of teacher-rated conduct problems (CP) and hurtful and uncaring behaviours (HUB) at age 6 and 10 with criminal convictions up to age 24 among 1593 males and 1423 females, and to determine whether aggressive behaviour at age 12 mediated the associations of CP and HUB with criminal convictions., Method: Teachers assessed HUB and CP at ages 6 and 10 and ratings above the 90th percentile at each age and within each sex were used to assign participants to 1 of 4 groups. Teachers assessed proactive, reactive, indirect, and verbal aggression at age 12. Juvenile and adult criminal records were obtained., Results: High CP and HUB males, aged 6, were 4 times more likely than males with lower ratings to acquire convictions for violent crimes and 5 times more likely to acquire convictions for nonviolent crimes by age 24. High HUB and CP females, aged 6, were 5 times more likely than females with lower ratings to have a conviction for a nonviolent offence by age 24. Among males, both aged 6 and 10, high HUB without CP were associated with elevations at risk of convictions for violent and nonviolent crimes, while among females the elevations at risk were limited to convictions for nonviolent crimes. Different types of aggressive behaviour mediated associations of high HUB and CP with subsequent criminal convictions, but not the association of HUB without CP and crime., Conclusions: Teachers in elementary schools rated behaviours that, from age 6 onward, significantly predicted criminal convictions into early adulthood.

Using a genetically informed design, this study examined the additive and interactive effects of genetic risk, personal peer victimization experiences, and peer victimization experienced by others on children's aggression and depression symptoms. Of major interest was whether these effects varied depending on whether or not the victimized others were children's close friends. The sample comprised 197 monozygotic and same-sex dizygotic twin pairs reared together (95 female pairs) assessed in Grade 4. Each twin's victimization experiences and victimization experienced by his or her friends and other classmates were measured using individuals' reports about their own levels of peer victimization. Aggression was assessed using peer nominations, and depression was measured using self-reports. Indicative of a possible social-learning mechanism or the emotional contagion of anger, multilevel regressions showed that personal victimization experiences were related to especially high levels of aggression when close friends where also highly victimized, albeit only in boys. Moreover, in line with social comparison theory, the effect of frequent personal victimization experiences on depressive feelings was much weaker when close friends were also highly victimized than when close friends were not or were only rarely victimized. Finally, a high level of peer victimization experienced by other classmates was related to a lower level of aggression in girls and boys, possibly because of a heightened sense of threat in classrooms where many suffer attacks from bullies. All of these results were independent of children's genetic risk for aggression or depression. Theoretical and practical implications are discussed., ((c) 2013 APA, all rights reserved.)

The main challenge in addressing the role of DNA methylation in human behaviour is the fact that the brain is inaccessible to epigenetic analysis in living humans. Using positron emission tomography (PET) measures of brain serotonin (5-HT) synthesis, we found in a longitudinal sample that adult males with high childhood-limited aggression (C-LHPA) had lower in vivo 5-HT synthesis in the orbitofrontal cortex (OBFC). Here we hypothesized that 5-HT alterations associated with childhood aggression were linked to differential DNA methylation of critical genes in the 5-HT pathway and these changes were also detectable in peripheral white blood cells. Using pyrosequencing, we determined the state of DNA methylation of SLC6A4 promoter in T cells and monocytes isolated from blood of cohort members (N = 25) who underwent a PET scan, and we examined whether methylation status in the blood is associated with in vivo brain 5-HT synthesis. Higher levels of methylation were observed in both T cells and monocytes at specific CpG sites in the C-LHPA group. DNA methylation of SLC6A4 in monocytes appears to be associated more reliably with group membership than T cells. In both cell types the methylation state of these CpGs was associated with lower in vivo measures of brain 5-HT synthesis in the left and right lateral OBFC (N = 20) where lower 5-HT synthesis in C-LHPA group was observed. Furthermore, in vitro methylation of the SLC6A4 promoter in a luciferase reporter construct suppresses its transcriptional activity supporting a functional role of DNA methylation in SLC6A4 promoter regulation. These findings indicate that state of SLC6A4 promoter methylation is altered in peripheral white blood cells of individuals with physical aggression during childhood. This supports the relevance of peripheral DNA methylation for brain function and suggests that peripheral SLC6A4 DNA methylation could be a marker of central 5-HT function.

Aggressive behavior in middle childhood is at least partly explained by genetic factors. Nevertheless, estimations of simple effects ignore possible gene-environment interactions (G × E) or gene-environment correlations (rGE) in the etiology of aggression. The present study aimed to simultaneously test for G × E and rGE processes between aggression, on the one hand, and peer victimization and the teacher-child relationship in school, on the other hand. The sample comprised 124 MZ pairs and 93 DZ pairs assessed in Grade 1 (mean age = 84.7 months). Consistent with rGE, children with a presumed genetic disposition for aggression were at an increased risk of peer victimization, whereas in line with G × E, a positive relationship with the teacher mitigated the genetically mediated expression of aggression., (© 2011 The Authors. Child Development © 2011 Society for Research in Child Development, Inc.)

This study used the monozygotic (MZ) twin difference method to examine whether differences in friends' aggression increased the differences in MZ twins' aggression and depressive symptoms from kindergarten to Grade 1 and whether perceived victimization by the friend played a mediating role in this context. Participants were 223 MZ twin pairs. Results showed that differences in kindergarten friends' aggression significantly predicted an increased difference in MZ twins' aggression from kindergarten (mean age = 6.7 years) to Grade 1 (mean age = 7.5 years) for both boys and girls. Differences in perceived victimization by the friend mediated this association, albeit only in boys. Differences in perceived victimization by the friend also predicted an increase in MZ twins' differences in depressive symptoms. These results support the importance of friendship experiences during early childhood., (© 2011 The Authors. Child Development © 2011 Society for Research in Child Development, Inc.)

There is growing evidence that among the different conduct disorder (CD) behaviors, physical aggression, but not theft, links to low neurocognitive abilities. Specifically, physical aggression has consistently been found to be negatively related to neurocognitive abilities, whereas theft has been shown to be either positively or not related to neurocognition. The specificity of these links needs further examination because attention deficit hyperactivity disorder (ADHD) links to both physical aggression and neurocognitive variation. The development of self-reported physical aggression and theft, from age 11 to 17 years, was studied in a prospective at-risk male cohort via a dual process latent growth curve model. Seven neurocognitive tests at age 20 were regressed on the growth parameters of physical aggression and theft. The links between neurocognition and the growth parameters of physical aggression and theft were adjusted for ADHD symptoms at ages 11 and 15 (parent, child and teacher reports). Results indicated that verbal abilities were negatively related to physical aggression while they were positively associated with theft. However, inductive reasoning was negatively associated with increases in theft across adolescence. Symptoms of ADHD accounted for part of the neurocognitive test links with physical aggression but did not account for the associations with theft. These differences emphasize the importance of examining specific CD behaviors to better understand their neurodevelopmental mechanisms. They also suggest that youth who engage in different levels of physical aggression or theft behaviors may require different preventive and corrective interventions., (© 2010 Wiley-Liss, Inc.)

Background: Investigating the latent structure of conduct disorder (CD) can help clarify how symptoms related to aggression, property destruction, theft, and serious violations of rules cluster in individuals with this disorder. Discovering homogeneous subtypes can be useful for etiologic, treatment, and prevention purposes depending on the qualitative or quantitative nature of the symptomatology. The aim of the present study is twofold: identify subtypes of CD in young adolescents based on latent class analysis (LCA) and investigate the two-year predictive validity of CD subtypes on deviant and criminal lifestyles., Methods: Adolescent-reported CD symptoms were collected using the National Longitudinal Survey of Children and Youth. Three cohorts of 12-13-year-olds were assessed during 1994-1995, 1996-1997, and 1998-1999 (N = 4,125)., Results: Latent class analyses yielded 4 distinct subtypes: No CD (82.4%); Non-Aggressive CD ('NACD', 13.9%); Physically Aggressive CD ('PACD', 2.3%); and Severe-Mixed CD ('SMCD', 1.4%). Predictive validity at age 14-15 was non-specific, although the SMCD type had, by far, the highest odds of deviant and criminal lifestyle outcomes in comparison to youth with PACD or NACD. NACD and PACD had similar odds of deviant outcomes, even if most NACD youth were subthreshold CD (fewer than three symptoms)., Conclusion: In early adolescence, CD is qualitatively and quantitatively heterogeneous, suggesting multiple developmental pathways. However, they appear to predict similarly violent and non-violent outcomes., (© 2010 The Authors. Journal of Child Psychology and Psychiatry. © 2010 Association for Child and Adolescent Mental Health.)

This study investigated the relation between theory of mind and reactive and proactive aggression, respectively, as well as the moderating role of peer victimization in this context. The 574 participants were drawn from a longitudinal study of twins. Theory of mind was assessed before school entry, when participants were 5 years old. Reactive and proactive aggression as well as peer victimization were assessed a year later in kindergarten. Results from multilevel regression analyses revealed that low theory of mind was related to a high level of reactive aggression, but only in children who experienced average to high levels of peer victimization. In contrast, a high theory of mind was related to a high level of proactive aggression. Again, this relation was especially pronounced in children who experienced high levels of peer victimization. These findings challenge the social skills deficit view of aggression and provide support for a multidimensional perspective of aggressive behavior.

Background: Adults exhibiting severe impulsive and aggressive behaviors have multiple indices of low serotonin (5-HT) neurotransmission. It remains unclear though whether low 5-HT mediates the behavior or instead reflects a pre-existing vulnerability trait., Methodology/principal Findings: In the present study, positron emission tomography with the tracer alpha-[(11)C]methyl-L-tryptophan ((11)C-AMT) was used to compare 5-HT synthesis capacity in two groups of adult males from a 21-year longitudinal study (mean age +/- SD: 27.1+/-0.7): individuals with a history of childhood-limited high physical aggression (C-LHPA; N = 8) and individuals with normal (low) patterns of physical aggression (LPA; N = 18). The C-LHPA males had significantly lower trapping of (11)C-AMT bilaterally in the orbitofrontal cortex and self-reported more impulsiveness. Despite this, in adulthood there were no group differences in plasma tryptophan levels, genotyping, aggression, emotional intelligence, working memory, computerized measures of impulsivity, psychosocial functioning/adjustment, and personal and family history of mood and substance abuse disorders., Conclusions/significance: These results force a re-examination of the low 5-HT hypothesis as central in the biology of violence. They suggest that low 5-HT does not mediate current behavior and should be considered a vulnerability factor for impulsive-aggressive behavior that may or may not be expressed depending on other biological factors, experience, and environmental support during development.

An experimental preventive intervention nested into a longitudinal study was used to test the developmental distinctiveness of proactive and reactive aggression. The randomized multimodal preventive intervention targeted a subsample of boys rated disruptive by their teachers. These boys were initially part of a sample of 895 boys, followed from kindergarten to 17 years of age. Semiparametric analyses of developmental trajectories for self-reported proactive and reactive aggression (between 13 and 17 years of age) indicated three trajectories for each type of aggression that varied in size and shape (Low, Moderate, and High Peaking). Intent-to-treat comparisons between the boys in the prevention group and the control group confirmed that the preventive intervention between 7 and 9 years of age, which included parenting skills and social skills training, could impact the development of reactive more than proactive aggression. The intervention effect identified in reactive aggression was related to a reduction in self-reported coercive parenting. The importance of these results for the distinction between subtypes of aggressive behaviors and the value of longitudinal-experimental studies from early childhood onward is discussed., ((c) 2010 Wiley-Liss, Inc.)

Differences in developmental trajectories of physical violence, vandalism, theft, and alcohol-drug use from ages 10 to 15 were studied. For females and for males, three trajectories of theft and of alcohol-drug use increased from 10 years to 15 years, while only the high trajectory of vandalism increased from ten to 14. All trajectories of physical violence decreased. Children who engaged in the high trajectories of vandalism, theft, and alcohol-drug use had a high probability of also being high in physical violence. Compared to males, females were less likely to be on the high trajectory of physical violence, and their trajectories of other antisocial behaviors were less strongly associated with high levels of physical violence. The results suggest that physical violence during pre-adolescence and adolescence has a different developmental pattern than other forms of antisocial behavior, and that its relation to these other forms of antisocial behavior differs by sex.

The goal of the present study was to examine whether controlling parenting contributes to the problem of physical aggression. Developmental trajectories of children's physical aggression were modeled from yearly teachers' ratings, from ages 6 to 12. Multinomial logistic regressions (N = 1,508) served to identify risk factors that distinguish children who display different levels of physical aggression throughout grade school. Results revealed that being a boy and having a reactive temperament were important child predictors. Parental separation and an early onset of motherhood were also significant risk factors. Finally, mothers' controlling parenting increased the odds of following the highest trajectory of physical aggression, above and beyond the previous risk factors.

Context: The co-occurrence of hyperactivity and conduct problems in childhood seems to increase the risk of early adulthood adjustment problems in males. However, little is known about this topic in females., Objectives: To describe the joint developmental trajectories of female hyperactivity and physical aggression during childhood and to examine the extent to which high trajectories of hyperactivity and physical aggression predict adjustment problems in early adulthood., Design, Setting, and Participants: A total of 881 females from a population-based sample were studied. Developmental trajectories were described using teachers' ratings of behavior problems from the age of 6 to 12 years., Main Outcome Measures: Age 21 years self-reports of substance use problems, criminal behaviors, aggression in intimate relationships, early pregnancy, educational attainment, and welfare assistance., Results: Between the ages of 6 and 12 years, the frequency of hyperactivity and physical aggression tended to decrease for most girls. Those on a trajectory of high hyperactivity (HH) and high physical aggression (HPA) and a trajectory of HH alone were significantly more likely to report nicotine use problems (odds ratio [OR], 2.16 [95% confidence interval {CI}, 1.30-3.56] and OR, 2.23 [95% CI, 1.39-3.58], respectively), mutual psychological aggression in intimate relationships (OR, 2.28 [95% CI, 1.24-4.18] and OR, 2.14 [95% CI, 1.19-3.85], respectively), and low educational attainment (OR, 4.09 [95% CI, 2.33-7.18] and OR, 3.21 [95% CI, 1.84-5.59], respectively) compared with the other females at the age of 21 years. Only the HH-HPA females were significantly more likely to report physical aggression (OR, 2.48 [95% CI, 1.41-4.37]) and psychological aggression (OR, 2.54 [95% CI, 1.48-4.36]) in intimate relationships, early pregnancy (OR, 2.31 [95% CI, 1.17-4.56]), and welfare assistance (OR, 2.68 [95% CI, 1.33-5.41]) compared with the other females., Conclusions: Elementary school girls with elevated levels of hyperactivity should be targeted for intensive prevention programs. These interventions should take into account the presence or absence of HPA.

Although peer victimization places children at serious risk for aggressive behavior, not all victimized children are aggressive. The diathesis-stress hypothesis of disease proposes that an environmental stressor such as peer victimization should to lead to maladjustment mostly in those individuals with preexisting genetic vulnerabilities. Accordingly, this study examined whether the link between peer victimization and child aggression is moderated by children's genetic risk for such behavior. Using a sample of 506 6-year-old twins, peer victimization was assessed through peer nominations and aggressive behavior was assessed through peer and teacher reports. Children's genetic risk for aggression was estimated as a function of their co-twin's aggression and the pair's zygosity. Genetic modeling showed that peer victimization is an environmentally driven variable that is unrelated to children's genetic disposition. Results also provided support for the notion of a gene-environment interaction between peer victimization and child's genetic risk for aggressive behavior, albeit only in girls. For boys, peer victimization was related to aggression regardless of the child's genetic risk for such behavior. Different socialization experiences in girls' compared to boys' peer groups may explain the different pattern of results for girls and boys.

Based on a sample of 406 seven-year-old twins, this study examined whether exposure to friends' social or physical aggression, respectively, moderates the effect of heritability on children's own social and physical aggression. Univariate analyses showed that children's own social and physical aggression were significantly explained by genetic factors, whereas friends' social and physical aggression represented "true" environmental factors that were unrelated to children's genetic dispositions. Multivariate analyses further suggested a possible gene-environment interaction in the link between friends' and children's physical aggression but not in the link between friends' and children's social aggression. Instead, friends' social aggression was directly related to children's social aggression, in addition to genetic effects on this behavior. Theoretical and practical implications of these results are discussed.

This study examined (a) the predictive link between peer victimization and children's reactive and proactive aggression, and (b) the potential moderating effect of reciprocal friends' reactive and proactive aggression in this context. The study also examined whether these potential moderating effects of friends' characteristics were stronger with respect to more recent friends compared to previous friends. Based on a convenience sample of 658 twin children (326 boys and 332 girls) assessed in kindergarten and first grade, the results showed that peer victimization uniquely predicted an increase in children's teacher-rated reactive aggression, but not teacher-rated proactive aggression. The relation of peer victimization to increased reactive aggression was, however, moderated by recent not previous reciprocal friends' similarly aggressive characteristics. These findings, however, tended to be mostly true for boys, but not for girls. The findings are discussed in terms of their theoretical and practical implications for victimized children's risk of displaying reactive and proactive aggressive behaviors.

Objective: To examine whether kindergarten children's genetic liability to physically aggress moderates the contribution of friends' aggression to their aggressive behaviors., Method: Teacher and peer reports of aggression were available for 359 6-year-old twin pairs (145 MZ, 212 DZ) as well as teacher and peer reports of aggression of the two best friends of each twin. Children's genetic risk for aggression was based on their cotwin's aggression status and the pair's zygosity., Results: Children's aggression was highly heritable. Unique environment accounted for most of the variance in friends' aggression, although there was also a small genetic contribution (15%). Both genetic liability to aggression and having aggressive friends predicted twins' aggression. However, the contribution of aggressive friends to children's aggression was strongest among genetically vulnerable children. This result was similar for boys and girls, despite sex differences in both aggression and the level of aggression of friends., Conclusions: Affiliation with aggressive friends at school entry is a significant environmental risk factor for aggression, especially for children genetically at risk for aggressive behaviors. Developmental models of aggression need to take into account both genetic liability and environmental factors in multiple settings, such as the peer context, to more precisely describe and understand the various developmental pathways to aggression. The implications for early prevention programs are discussed.

It has been proposed that aggressive behavior may result from unrealistically positive self-evaluations that are disputed by others (Baumeister, Smart, & Boden, 1996). The present three studies tested this proposition concurrently and longitudinally for the domain of self-perceived social competence (SPSC) in 3-6th grade children on two continents. Each study tested whether aggressive behavior is related to general overestimation of SPSC compared to competence as perceived by peers, or to disputed overestimation, that is, overestimation disputed through rejection by peers. Specificity of relations with reactively or proactively aggressive behavior patterns was assessed and the predictive value of overestimation to the development of these types of aggressive behavior was investigated. Concurrently, disputed overestimation explained more variance in aggressive behavior than general overestimation, and was uniquely related to proactive aggression. Longitudinally, disputed overestimation also uniquely predicted changes in proactive, not reactive aggression.

This study compared the contribution of genes and environment to teacher-rated reactive and proactive aggression in 6-year-old twin pairs (172 pairs: 55 monozygotic girls, 48 monozygotic boys, 33 dizygotic girls, 36 dizygotic boys). Genetic effects accounted for 39% of the variance of reactive aggression and for 41% of the variance of proactive aggression. The remainder of the variance was explained by unique environmental effects. Genetic as well as unique environmental effects were significantly correlated across reactive and proactive aggression (genetic correlation = .87, environmental correlation = .34), but this overlap was largely due to a common underlying form of aggression (i.e., teacher-rated physical aggression). Once common etiological factors due to physical aggression were accounted for, reactive and proactive aggression shared no other genes and only a few environmental influences, although additional specific genetic and environmental effects were observed for both reactive and proactive aggression. These specific effects indicate that both reactive and proactive aggression may be influenced mostly by socialization experiences that are specific to each type of aggression and only to a very small degree by specific genes.

The goal of this study was to examine the links between difficult temperament (i.e., negative emotionality) and harsh parental discipline during toddlerhood, and reactive and proactive aggression in kindergarten. These links were assessed on a longitudinal population-based study of 1516 boys and girls followed longitudinally from the age of 17 months through the age of 72 months. Two possible models were tested to examine the interplay between negative emotionality and harsh parenting in predicting later reactive aggression compared to proactive aggression. The first was an additive model where both aspects make unique contributions in predicting later reactive aggression. The second model was an interactive model where harsh parenting exacerbates the link between negative emotionality and reactive aggression. Results showed a specific contribution of negative emotionality to reactive aggression. The results relative to harsh parenting are more mixed but nonetheless in line with developmental models stressing different pathways to reactive and proactive aggression.

Background: Different developmental courses have been postulated for proactive and reactive aggression., Objective: Investigated the developmental course of proactive and reactive aggression in a large sample of adolescent boys from low socioeconomic areas., Method: A dual group-based joint trajectory method was used to identify distinct trajectories as well as similarities and differences in intra-individual changes., Results: The trajectories for proactive and reactive aggression were similar: the majority of individuals followed infrequent and desisting trajectories. Contrary to expectations, very few adolescents followed trajectories of increasing proactive aggression. Reactive aggression was more common than proactive aggression. The overlap in trajectory group membership of individuals following trajectories of high peaking proactive and reactive aggression was nearly 100%. Across a period of 5 years, the boys on the high peaking trajectories were twice as likely to have affiliated with gangs., Conclusions: The developmental courses of proactive and reactive aggression are similar during adolescence. Males who tend to frequently use one form of aggression throughout adolescence also tend to frequently use the other and are at an increased risk for contemporaneous delinquent lifestyles.

Testosterone (T) has been found to have a stimulating effect on aggressive behavior in a wide range of vertebrate species. There is also some evidence of a positive relationship in humans, albeit less consistently. In the present study we investigated the relationship between T and aggression, dominance and delinquency over time, covering a period from early adolescence to adulthood. From a large population-based sample (n = 1.161) a subgroup of 96 boys was selected whose behavior had been assessed repeatedly by different informants from age 12 to 21 years, and who had provided multiple T samples over these years of assessment. On the whole, a decrease in aggressive and delinquent behavior was observed in a period in which T rises dramatically. Boys who developed a criminal record, had higher T levels at age 16. In addition, positive associations were observed between T and proactive and reactive aggression and self-reported delinquent behavior. Over the pubertal years different forms of aggressive and delinquent behavior were positively related to T, which may indicate that specific positive links are dependent on the social setting in which this relationship is assessed.

Background: This study examined the elevated heart rate (HR) response to alcohol intoxication, thought to reflect an increased sensitivity to alcohol-induced reward, as a potential factor in the increased likelihood of alcohol-induced aggression., Methods: Three groups, intoxicated high (n=37) and low (n=37) HR responders and sober controls (n=73), participated in a laboratory measure of physical aggression, the Taylor Aggression Paradigm., Results: Results revealed that intoxicated high HR responders were more aggressive than the intoxicated low HR responders and sober controls., Conclusions: These findings are interpreted within a hypothetical model relating increased alcohol-induced aggression to a dysregulation in the motivational system responding to rewards.

Using a genetic design of 234 six-year-old twins, this study examined (a) the contribution of genes and environment to social versus physical aggression, and (b) whether the correlation between social and physical aggression can be explained by similar genetic or environmental factors or by a directional link between the phenotypes. For social aggression, substantial (shared and unique) environmental effects but only weak genetic effects were found. For physical aggression, significant effects of genes and unique environment were found. Bivariate modeling suggests that social and physical aggression share most of their underlying genes but only very few overlapping environmental factors. The correlation between the two phenotypes can also be explained by a directional effect from physical to social aggression.

This study examined (a) the links between children's overly positive perceptions about the relations with the peer group and with their best friend to subsequent behavioral, emotional, and social adjustment, and (b) whether these links are moderated by children's aggression. Using a short-term longitudinal design, the study was based on a sample of 819 4th- to 6th-graders (427 girls) from low to average SES families. Results showed that positive illusions about their social relations with classmates and with friends were related to an increase in children's peer-rated social preference and fostered the stability of children's dyadic friendships, regardless of children's level of aggression. In addition, overestimation of social competence with the peer group and overestimation of friendship quality were both related to a decrease in children's depressive feelings. Extreme overestimation as well as extreme underestimation of social competence with the peer group was also related to an increase in children's aggression. This latter result, however, was only true for children who were highly aggressive to begin with. The theoretical and practical implications of these results are discussed.

Some sons of male alcoholics (SOMAs) are characterized by an increased heart rate (HR) response to alcohol intoxication, which is thought to reflect increased sensitivity to alcohol-induced reward. Such a response has also been related to increased physical aggression. However, the confounding effect of aggression in SOMAs may be obscuring the interpretation of these findings. The HR response to alcohol was therefore assessed in 4 groups: high/low aggressive SOMAs and high/low aggressive non-SOMAs. Results indicate that aggressive SOMAs had the highest intoxicated HR response and that they reported the most alcohol consumption. This suggests that in some cases the high comorbidity between alcohol misuse and aggression is related to an increased sensitivity to alcohol-induced reward.