Genetic Theories of Criminality: Chromosomal and Twin Studies
Chromosomal abnormalities play a significant role in understanding criminal behavior, particularly the XYY syndrome in males. While XX chromosomes determine female characteristics and XY determines male characteristics, an extra Y chromosome has been linked to increased aggression and violent tendencies.
Definition: Concordance rate refers to the percentage similarity between pairs of twins exhibiting particular behavioral traits or disorders.
Twin studies provide compelling evidence for genetic influences on criminal behavior. Monozygotic (identical) twins share 100% of their genes and the same environment, while dizygotic (non-identical) twins share 50% of their genes and the same environment. Research shows higher concordance rates for criminal behavior between monozygotic twins compared to dizygotic twins, suggesting a genetic component.
Landmark studies support these findings. Christiansen's 1977 examination of 3,500 twin pairs in Denmark revealed that while concordance rates were present, environmental factors played a substantial role. Similarly, Lang's 1929 study of 30 twin pairs showed that among 13 monozygotic pairs, 10 pairs both exhibited criminal behavior, while among 17 dizygotic pairs, only 2 pairs showed matching criminal tendencies.
Highlight: While genetic factors influence criminal behavior, they are not deterministic. Environmental factors play a crucial role in shaping criminal tendencies.