Creating a social world: a developmental twin study of peer-group deviance.
BACKGROUND
Peer-group deviance is strongly associated with externalizing behaviors. We have limited knowledge of the sources of individual differences in peer-group deviance.


OBJECTIVE
To clarify genetic and environmental contributions to peer-group deviance in twins from midchildhood through early adulthood.


METHODS
Retrospective assessments using a life-history calendar. Analysis by biometric growth curves.


METHODS
General community.


METHODS
Members of male-male pairs from the population-based Virginia Twin Registry personally interviewed in 1998-2004 (n = 1802).


METHODS
Self-reported peer-group deviance at ages 8 to 11, 12 to 14, 15 to 17, 18 to 21, and 22 to 25 years.


RESULTS
Mean and variance of peer-group deviance increased substantially with age. Genetic effects on peer-group deviance showed a strong and steady increase over time. Family environment generally declined in importance over time. Individual-specific environmental influences on peer-group deviance levels were stable in the first 3 age periods and then increased as most twins left home. When standardized, the heritability of peer-group deviance is approximately 30% at ages 8 to 11 years and rises to approximately 50% across the last 3 time periods. Both genes and shared environment contributed to individual differences in the developmental trajectory of peer-group deviance. However, while the correlation between childhood peer-group deviance levels and the subsequent slope of peer-group deviance over time resulting from genetic factors was positive, the same relationship resulting from shared environmental factors was negative.


CONCLUSIONS
As male twins mature and create their own social worlds, genetic factors play an increasingly important role in their choice of peers, while shared environment becomes less influential. The individual-specific environment increases in importance when individuals leave home. Individuals who have deviant peers in childhood, as a result of genetic vs shared environmental influences, have distinct developmental trajectories. Understanding the risk factors for peer-group deviance will help clarify the etiology of a range of externalizing psychopathology.
Kendler
Kenneth S
KS
Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University Medical School, VA 23298-0126, USA.
Jacobson
Kristen C
KC
Gardner
Charles O
CO
Gillespie
Nathan
N
Aggen
Steven A
SA
Prescott
Carol A
CA
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000987:Antisocial Personality Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D001699:Biometry / Q000379:methods; D002648:Child; D002653:Child Behavior Disorders / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D005195:Family Relations; D005260:Female; D005824:Genetics, Behavioral; D006801:Humans; D007206:Individuality; D008137:Longitudinal Studies; D008297:Male; D008957:Models, Genetic; D015233:Models, Statistical; D010379:Peer Group; D012307:Risk Factors; D012931:Social Environment