JV

CHAPTER 3

Genetics and Antisocial Behavior

  • Two main categories: behavior genetics and molecular genetics.

  • Behavior genetics: Examines the role genes play in behavior development, distinguishing genetic from environmental influences.

  • Molecular genetics: Studies gene structure and function at the molecular level, focusing on specific genes.

Behavior Genetics

  • Views behavioral differences as stemming from genetic effects, shared environmental influences, and unshared environmental experiences.

  • Twin studies compare identical (MZ) and fraternal (DZ) twins to determine the role of genetics in criminality.

  • DZ twins develop from two different fertilized eggs and are no more genetically alike than nontwin siblings.

  • MZ twins develop from a single egg and share the same genes.

  • MZ twins sharing the same chorion are more similar in personality and cognitive ability.

Twin Studies

  • Twin and adoption studies support the heritability of antisocial behavior.

  • Genes influence approximately 50% of the population variation in antisocial behavior.

  • Environmental influences can change gene expression, altering brain functioning and behavior.

  • Psychosocial influences can result in structural modifications to DNA.

  • Peer interactions, neglect, abuse, and brain injuries can have negative influences.

  • Supportive parenting can neutralize antisocial behavior, even in genetically vulnerable children.

Shared and Nonshared Environments

  • Shared environments: Prenatal and life experiences affecting both twins, promoting similarity.

  • Nonshared environments: Different living experiences for each twin, contributing to uniqueness.

  • Nonshared environments account for approximately 30% of the variation in antisocial behavior.

  • Genetic and nonshared environmental influences increase with age, while shared environmental influences decrease.

Concordance

  • Concordance is the degree to which related pairs of subjects both show a particular behavior or condition, expressed in percentages.

  • Early twin studies indicated heredity may be a determinant of intelligence, schizophrenia, and criminal behavior.

  • Higher criminal concordance for identical twins compared with fraternals.

Twins Early Development Study (TEDS)

  • Longitudinal research in the UK involving twins born in 1994-1996.

  • Explores behavior problems and development in language, cognition, and academic abilities.

  • Nature and nurture contribute to human behavior.

  • Heritability plays a modest role in antisocial behavior.

  • Callous-unemotional trait shows high heritability and little shared environmental influence.

Twin Study of Child and Adolescent Development (TCHAD)

  • Longitudinal research using data from the Swedish Twin Registry.

  • Genetic factors played an important role in early-onset aggression.

Adoption Studies

  • Adoption studies help identify environments conducive to criminality.

  • Adoptive parents and their adopted children are not genetically related.

  • Follow-up of persons relinquished for early adoption by female offenders.

  • Positive correlation between antisocial tendency and child’s age at adoption and time in temporary care.

Molecular Genetics

  • Molecular genetics aims to identify genes predisposing to antisocial behavior.

  • MAOA gene plays a role in preventing antisocial behavior.

  • Low activity form of the MAOA gene (MAOA-L) is linked to aggression and violence, nicknamed “the warrior gene.”

  • At least seven genes associated with antisocial behavior in humans.

  • These genes contribute to impairments in brain structure and function.

  • Structural or functional problems in the prefrontal cortex are associated with impulsively violent offenders.