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+support for the diathesis-stress model of offending
Sarnoff Mednick et al: study of 13,000 Danish adoptees (neither biological nor adoptive parents were convicts)
13.5% adoptees had convictions
20% adoptees had convictions when biological parent had convictions
24.5% adoptees had convictions when both B & A parents had convictions
Shows genetic influence and environmental factors play an important role in offending
-problem with twin studies
Assumption underlying twin studies that environments of MZ & DZ twins are equivalent
Joseph: pointed out that MZ twins are treated more similarly
So differences in concordance rate could reflect environmental difference that distinguish each type of twin
Twin studies lack internal validity
-problems with adoption studies
Stress prior to birth can affect development to foetus
Even if child is adopted early, influence of environment cannot be controlled for
Adoption studies lack internal validity
Weakens source of evidence to support genetic explanation of offending behaviour
-genetics explaining offending behaviour is incompatible with way in which our legal system operates
In court of law, offenders are held morally responsible for their actions
Debatable whether individuals genetic make up could be used as a defence in criminal cases