Unit Two: Biological Theories of Criminality

Study Notes

Biological Theories of Criminality

Biological theories assert that an individual's nature significantly influences criminal behavior, emphasizing physical and genetic traits.
These theories imply that specific characteristics could increase the likelihood of committing crimes.

Genetic Theories

Genetic theories concentrate on an individual's genetic makeup, proposing that aggressive behavior may be genetically inherited.
Certain genetic abnormalities may predispose some individuals to exhibit aggressive tendencies.

Genes

Genes are segments of DNA responsible for directing cell growth and functions in the body.
Genetic similarity to an aggressive person increases the likelihood of exhibiting aggression.
Sex determination occurs via the 23rd chromosome pair, with XX indicating female and XY indicating male.

Jacobs XYY Theory

Humans have 46 chromosomes total, with two determining sex (XX or XY).
XYY syndrome involves an extra Y chromosome in males, leading to 47 chromosomes.
Often called "super males," individuals with XYY syndrome may experience elevated testosterone, aggression, lower IQ, and learning difficulties.
Among the male prison population, the incidence of XYY syndrome is 1.5%, compared to 0.1% in the general population.

Case Study - Jacob's XYY Theory

John Wayne Gacy, a notorious American serial killer, had XYY syndrome used in his legal defense.

Evaluation Supporting Jacob's XYY Theory

Research indicates a notable prevalence of XYY chromosomes among the prison population.
Findings suggest a genetic factor may contribute to aggressive and violent behavior.

Evaluation Criticizing Jacob's XYY Theory

Genetic abnormalities are common in the general population and do not solely explain aggression.
Overemphasis on genetics may ignore behavioral and environmental factors.
Research by Theilgard found no association between XYY status and aggression levels.

Twin Studies

Monozygotic (MZ) twins share 100% of their DNA, while dizygotic (DZ) twins share 50%.
The Kray twins were infamous gangsters known for violent crimes.
Higher concordance rates for criminal behavior are often observed in MZ twins compared to DZ twins.
Research by Lagne revealed higher concordance rates for criminal behavior among MZ twins, while Christiansen studied over 3,500 twin pairs in Denmark for similar behavior patterns.

Evaluation Supporting Twin Studies

Twin studies are considered natural experiments, as twin relationships develop independently of researchers.
Christiansen's findings indicate a genetic component to criminality.
Results have also contributed to understanding the prevention of certain disorders.

Evaluation Criticizing Twin Studies

Earlier studies, like Lagne's, lacked rigor in determining whether twins were MZ or DZ, affecting validity.
Samples in twin studies might not represent the general population.
Shared environments may influence behavior, indicating nurture plays a significant role alongside nature.

Adoption Studies

Adoption studies are crucial for understanding nature versus nurture, as adopted children are raised in different environments from their biological parents.

Description

Explore the biological theories that explain the link between a person's physical characteristics and criminal behavior. This quiz focuses on various genetic theories and their implications for understanding criminality. Test your knowledge and discover how biology and genetics may contribute to crime.