Psychology and the Law 4/15/2012
Chapter 2 – Theories of Crime: Biological and Evolutionary Explanations:
What makes a strong Theory?
- A theory is simply is an explanation of a particular phenomenon, in our case, antisocial behavior.
1. it is parsimonious
2. Clearly identifies the casual mechanisms and corresponding mediators and moderators
underlying the phenomenon of interest
3. is testable and hence falsifiable via hypotheses and predictions
4. is based on empirical data and is modified in response to new data
5. possesses interdisciplinary compatibility
6. respects gender, ethnicity and culture
A. Historical Context –
Franz Gall was the founding father of phrenology -- a theoretical perspective positing that there is a
relationship between the shape and size of a person’s head and his/her personality, mental ability and
Cesare Lombroso, took Gall’s work one step further and began comparing criminals- both men and
women as well as prostitutes- to “normal” segments of the population .
o Lombroso argued criminals’ posses distinctive physical features such as sloping foreheads
and twisted lips often not observed in his “normal” subjects.
o He referred to these features as atavisms and suggested that criminals were evolutionary
throwbacks who had more in common with Neanderthals than modern-day man.
** Lombroso remains father of criminology
Francis Galton: founded eugenics – the theory that was ultimately responsible not only for the forced
sterilization of thousands of individuals deemed “ unfit” to reproduce in the U.S during the early part
of the twentieth century, but also for the atrocities that occurred under Hitler’s regime – forced
abortion, sterilization and ultimately, death camps.
Genetics and Crime – twins, adoption and molecular genetics
A concordance rate of 30 percent for the DZ twins would mean that if one of the DZ twins was
“criminal,” then there was a 30 percent chance that the other DZ twin was also criminal.
o Similarly, a concordance rate of 70 percent for the MZ twins would mean that if one of the
MZ twins was “criminal,” there was 70 percent chance that the other MZ twin was also
o Evidence for a genetic contribution to crime is inferred if concordance rates are higher
among MZ than DZ twins.Psychology and the Law 4/15/2012
Adoption research has taken one of two forms: 1) parent-offspring adoption studies; and 2) sibling-
offspring adoption studies.
a) In the parent-offspring paradigm, concordance rates (or correlations) between adoptive
parents and adoptees’ antisocial behavior are compared to concordance rates between
biological parents and adoptees.
- If the concordance rates/correlations are higher for the biological parents
and the adopted offspring than the adoptive parents and the adopted
offspring, genetic contributions to antisocial behavior are inferred.
Adoption studies are not without limitations, which include:
1) Generalizability problems given that adoptees have higher rates of antisocial behavior relative to
the rest of the population; and
2) That the environments of adopted offspring tend to be more advantageous relative to the general
population, thereby potentially reducing shared environmental effects due to restricted range.
Molecular Genetics Research:
The MAOA gene is located on the X chromosome; hence it is sex-linked.
• The MAOA gene is responsible for encoding the MAOA enzyme, which in turn is responsible
for metabolizing or breaking down key brain NTs such as NE, serotonin, and dopamine,
• All of which have been implicated in aggression and various forms of antisocial behavior.
The two existing versions of the MAOA gene – low activity and high activity are the result of
Caspi et al. used a methodologically rigorous design to test the MAOA gene by environment
- They followed an entire cohort from birth until age 26 in the small New Zealand town of
- Researchers found evidence for a strong gene by environment interaction across all four measures
of antisocial behavior- conduct disorder, violent convictions, violent disposition, and antisocial
personality disorder symptoms.
Neurochemistry and Crime – Hormones and Neurotransmitters
• A steroidal hormone within the family of androgens
• It is responsible for developing and maintaining male primary and secondary sexual
• The relationship between aggression and testosterone is positive but weak.
• Testosterone levels fluctuate in the morning and stabilize during the afternoon and
2. SerotoninPsychology and the Law 4/15/2012
• Chemical formula : 5-HT ( hydroxytryptamine)
• Plays a role in behavioral inhibition and mood regulation
• It is produced from an essential amino acid : tryptophan
• Malfunctioning serotonin system results in : impulsivity, irritability and aggression
• Release of dopamine causes feelings of pleasure that accompany factors such as sex, love
• The dopamine pleasure centre can be triggered artificially with illicit drugs, alcohol and
nicotine – which are known to increase aggression.
• Dopamine/aggression relationship can be explained by the following
Individuals with low levels of dopamine require greater levels of stimulation to
Hence, they are more likely to develop addictions to illicit drugs such as