PSYC39 – Ch.2 Theories of Crime: Biological and Evolutionary Explanations
- Focuses on biological and evolutionary explanations for antisocial
behaviour, crime and related phenomena.
- Biological explanations are varied: genetics exemplified by twin and
adoption studies, brain neurochemistry and importance of diet.
What makes a strong theory?
- Clearly identifies the causal mechanisms and corresponding mediators
and moderators underlying the phenomenon of interest
- Testable and falsifiable via hypotheses and predictions
- Based on empirical data and is modified in response to new data
- Possesses interdisciplinary compatibility
- Respects gender, ethnicity and culture
- Franz Gall (1758-1828) was the 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
- Like most phrenology-oriented researchers at the time, Spurzheim
(student of Gall) failed to include a comparison group, e.g. women who
had not killed their children.
the ‘science’ of phrenology eventually died out.
- Cesare Lombroso (1835-1909) was the father of criminology. He took
Gall’s work one step further and began comparing criminals to ‘normal’
segments of the population.
- Lombroso proposed that criminals possess distinctive physical features
and referred to the features as atavisms. e.g. sloping foreheads and
twisted lips often not observed in his normal subjects. He suggested that
criminals were evolutionary throwbacks who had more in common with
Neanderthals than modern-day man.
- Charles Darwin posited that humans had evolved from ancestral species
via the mechanisms of natural selection. (Published on the1st volume of
The Criminal Man). But others began to misuse his work
- Francis Galton founded eugenics – the theory that was ultimately
responsible for the forced sterilization (or worse) of thousands of
individuals deemed ‘unfit’ to reproduce in the US during the early part of
the 20 century, and for the atrocities that occurred under Hilter’s regime
– forced abortion, sterilization and death camps.
(The science of improving a human population by controlled breeding to
increase the occurrence of desirable heritable characteristics. Developed
largely by Francis Galton as a method of improving the human race.)
- Anderson (2007) demonstrates that the study of biology and evolution
has advanced considerably since Darwin and Lombroso. It is becoming
increasingly clear that biology is not destiny Researching biological explanations of crime
- Researchers often define crime using current legal definitions and
examine whether biological factors correlate or predict official criminal
offending in the form of arrests or convictions.
- Targets of study are varied. E.g. some focusing on males; others on
females, children, adolescents, or specific groups of offenders such as
violent of sexual.
- Research methods and participant pools are vast and complex.
Genetics and Crime – Twins, adoption, and molecular genetics
- Behavioural genetics (relies heavily on the study of twins and
adoptions) can help separate genetic from environmental influences
- the percentage of DNA that humans collectively share, 99%, is fixed,
accounting for our basic similarities. Behavioural genetics focuses on the
remaining 1% of the variance that is free to vary.
- Monozygotic (MZ) twins (identical) are genetically identical; Dizygotic
(DZ) twins (fraternal) sharing on average only 50% of that free-to-vary-
- In the earliest forms of twin studies, research would identify sample of
MZ and DZ twins, both raised by their respective biological families and
obtain some estimate of criminal behavioiur via self-report or official
Concordance rates would be calculated separately for MZ and DZ twins
Evidence for a genetic contribution to crime is inferred if concordance
rates are higher among MZ than DZ twins.
- Concordance rates are typically converted into a heritability coefficient
- descriptive statistics that represents the proportion of phenotypic
variance in a given behvaiour, e.g. criminal, in a sample that can be
attributed to genetic variation among individual.
- Recently, more complex statistical appraches such as biometic modeling
have been used to estimate heritability coefficient.
- Biometic modeling – permit the estimation of two types of
environmental factors: shared environmental factors and non-shared
environmental factors (exposure to different peer groups or differential
treatment by parents).
contrary to popular belief that genetics studies are just as much about
genes as they are about environment
- Common criticism against twin study: may overestimate (sometimes
underestimate) the genetic contribution for several reasons.
- 1. Parents are arguably more likely to provide similar environments for
MZ twins than DZ counterparts, thus artificially inflating the genetic
(this problem us remedied by ‘natural experiments’, where MZ twins have
been separated at birth and reared apart)
- 2. Heritability estimates for MZ twins may be confounded by prenatal
favtors = not necessarily genetic e.g. MZ twins usually have one placenta and DZ twins usually have two
separate placentas, thereby introducing a potential biological difference
that is not necessarily genetic.
- two forms: parent-offspring adoption studies & sibling-offspring adoption
- Parent-offspring paradigm: concordance rates/correlations between
adoptive parents and adoptees’ antisocial behaviour are compared to that
between biological parents and adoptees.
if concordance rates are higher for biological parents and adopted
offspring, genetic contributions to antisocial behaviour are inferred.
- Related variation of the design is the cross-fostering paradigm. Adopted
children have biological parents who were criminal/non-criminal OR
adoptive parents who were criminal/non-criminal
- Sibling-offspring paradigm, concordance rates between adoptive
siblings are compared with that between biological siblings
- Mednick et all (1984) performed a particularly strong adoption study of
14427 non-familial adoptions in Demark (1927-47). Ascending order of
criminality of the offspring
BP and AP were not criminal
AP ys, BP no
BP ys, AP no,
BP and AP YES.
Results show that both genetics and environment both contribute to
variance in antisocial behaviour
- Limitations of adoption studies:
1. generalizability problem given that adoptees have higher rates of
antisocial beh relative to the rest of the population
2. The environments of adopted offspring tend to be more advantageous
relative to the general population. Which potentially reducing shared
environmental effects due to restricted range
- Research increasingly show that the gene-crime link is most likely not a
direct conduit, but a function of the meditational effects of inherited
characteristic that predispose an individual to antisocial behaviour, e.g.
lower intelligence, impulsivity, ADHD.
- antisociality often results from a series of complex interactions
between numerous factors.
Molecular Genetics Research
- Caspi and colleagues (2002) published a study demonstrating an
interaction between a specific gene and a well-known risk factor –
childhood maltreatment. The study was epidemiological in nature.
They studied how the low-activity version of monoamine oxidase A
(MAOA) may or may not intensity the effects of childhood maltreatment.
- The MAOA gene is responsible for encoding the MAOA enzyme, which in
turn is responsible for metabolizing or breaking down key brain
neurotransmitters such as norepinephrine, serotonin, and dopamine. All of which have been implicated in aggression and various forms of
- Two existing versions of the MAOA gene = low activity and high activity,
are the result of polymorphism
- Result: over 80% of youth classified as having low MAOA activity and as
being severely maltreated were classified as conduct disordered; only 40%
with high MAOA activity plus severe maltreatment were conduct
while maltreatment by itself had deleterious effects, its effects were
exacerbated by the presence of a low-activity MAOA gene.
- Foley et all (2004), Frazzetto et al. (2007) replicated Caspi et al’s findings
- Increasing evidence show that the low-activity version of the MAOA gene,
sometimes dubbed the ‘warrior gene’ played a significant role in the
expression of antisocial behaviour, particularly aggression and violence.
* the low activity MAOA gene only expresses itself in the presence of
certain environmental cues, e.g. childhood abuse or provocation.
Neurochemistry and Crime – Hormones and Neurotransmitters
Hormones and Crime
- the endocrine system governs more than 50 hormones in the human
body. Hormones are released into our bodily fluids (typically via the
bloodstream) by nine primary glands.
- Hormones not only regulate metabolism, growth, and development and
- Testosterone is one particular hormone implicated in criminal behavior,
e.g. violence and aggression. Studies found that younger males have
higher level of testosterone; and testosterone levels fluctuate more in the
morning and stabilizes in the afternoon and evening, thus higher level as
- In physical and chemical castration studies shown that sexual re-
offending is reduced in offenders. Suggesting the relationship between
testosterone and sexual aggression may be more than correlational.
- Premenstrual syndrome (PMS) has been used (albeit rarely) successfully
as a legal defense in Britain and the US, and as a mitigating factor in
PMS – related to aggression (p.40 for more details)
Neurotransmitters and Crime
- Like hormones, neurotransmitters are chemical messengers that operate
in the brain. Neurotransmitters are the messengers of the nervous
- Three neurotransmitters in particular have been studied in relation to
crime: serotonin, dopamine, and norepinephrine
- The neurotransmitter sertotonin, or hydroxytryptamine (5-HT) plays an
important role in behavioural inhibition and mood regulation. It is
produced from an essential amino acid, tryptophan.
- Research has shown that there is a link between a malfunctioning
serotonin system and impulsivity, irritability and aggression (directed at self or others).
Malfunctioning serotonin systems: low levels of serotonin, low levels of
its precursors such as tryptophan, low levels of its metabolites (once
neurotransmitter has completed its job it breaks down into metabolites),
and faulty serotonin receptor sites on the postsynaptic neuron.
- Moore, Scarpa and Raine’s (2002) meta-analytic review of 16 studies, on
average serotonin levels (as measured via cerebro-spinal fluid, CFS
serotonin metabolites) were substantially lower among antisocial
individuals than non-antisocial individuals.
the effect was even more pronounced for individuals under the age of 30.
- In Moffitt et al. (1998)’s epidemiological research design, results show a
moderate (positive) correlation between blood serotonin levels and
violent criminal behaviour for men but not women.
there is a correlational link between a malfunctioning serotonin system
- Studies that artificially manipulate the level of tryptophan and then
examine its impact on aggression in a lab setting suggest a causal link.
Other studies suggest that serotonin may exert its influence indirectly on
aggression through the mediator of impulsivity or perhaps negative
mood. Potential treatment implications suggest that changes in diet could
Anyhow, these researches remain preliminary.
- Dopamine release causes feelings of pleasure that accompany factors like
sex, love and food.
- More research is needed to fully understand the role that dopamine plays
in antisocial behaviour, particularly aggression.
it is possible that dopamine exerts its influence indirectly via other
neurotransmitters, e.g. serotonin and norepinephrine as dopamine also
Another hypothese is that individuals with low level of dopamine require
greater levels of stimulation to experience pleasure – more likely to
develop addictions to illicit drugs like cocaine that quickly increase
dopamine levels and create an immediate high, but also have the side
effect of increasing aggressive tendencies.
- Norepinephrine signals the body to react to short-term stress by
increasing heart rate and blood pressure.
- Limited research suggests that high levels of norepinephrine are
correlated with aggression.
further investigation is needed to determine the exact role of
norepinephrine in antisocial behaviour.
Psychophysiology and Crime
- Psychophysiology theory uses physiology (low resting heart rate) to
explain psychological (emotion, motivation, learning) constructs.
- Some psychophysiological theories try to link measures of autonomic
response (heart rate, electrodermal activity/galvanic skin response/ skin
conductance) to various measures along the antisocial spectrum
- Electrodermal activity(EDA) measures the amount of electrical current
between 2 points on the skin. - Gray’s arousal model (based largely on animal modStuels of behaviour)
hypothesized that personality, learning, motivation, and emotional
response are largely governed by two underlying biological systems of
autonomic arousal: the behavioural activation system (BAS) and the
behavioural inhibition system (BIS).
- BIS – an