1. GENETIC INFLUENCES ON HUMAN BEHAVIOR
HISTORICAL ORIGINS, TWIN STUDIES, ADOPTION STUDIES, AND FAMILY STUDIES

2. Historical Origins
People have always wanted to know why we behave the way we do. In the past, human behavior was explained and predicted in a variety of interesting ways:
Astrology: Studying the relationship between astronomy and humans to explain personalities.
Phrenology: Studying the bumps on people’s heads and the shape of their skulls to predict behavior.
Palmistry: Analyzing a person’s character and future by examining the lines on his or her palm (palm reading).

3. Historical Origins II
Cesare Lombroso ( ), “the father of criminology,” believed that criminals were throwbacks to a more primitive evolutionary time and could be identified by their outward physical appearances.
Believed that criminals typically had huge jaws, eye defects, strange shaped noses, protruding lips, sloped foreheads.
They were born defective; and biologically inferior people.
Blamed criminality on the person, not society or social conditions (inequality, poverty, etc.)

4. Historical Origins III
Victorian scientist Sir Francis Galton ( ) began to explore inheritance and coined the term “nature vs. nurture.”
Galton wanted to know if genius was hereditary, so he conducted studies that sought to apply Charles Darwin’s research about evolution in plants and animals to humans.
His work eventually became its own field of study, which he called eugenics.

5. Eugenics
Galton defined eugenics as, “"the study of all agencies under human control which can improve or impair the racial quality of future generations.”
The modern definition of eugenics is: “science that seeks to promote genetic/biological improvement of human society by influencing who does and does not reproduce.
Eugenics programs and policies have included: genetic screening, birth control, promoting differential birth rates, marriage restrictions, segregation (both racial segregation and segregation of the mentally ill from the rest of the population), compulsory sterilization, forced abortions or forced pregnancies, and genocide.

6. Examples of Eugenics
At the Nuremburg Trials, several Nazis justified their role in the Holocaust by stating their belief in eugenics.
U.S. sterilization of people with disabilities (VA Sterilization Act of 1924, upheld by the Sup. Ct. and only repealed in 1974).
U.S. anti-miscegenation laws (repealed by the Sup. Ct. in 1967).

7. Modern Understandings
Modern scientists generally understand that both genetics and environmental influences play a role in our behavior. We will talk more about environment in the next unit. Two major theories that suggest the interaction between genetics and environment are:
PEN Model: Psychoticism, Extraversion, Neuroticism->these heritable traits can predict predisposition to criminal behavior.
General Arousal Theory of Criminality: Individuals with low arousal levels are predisposed to criminal behavior; without adequate stimulation they will seek out high-risk activities.

8. Behavioral Genetics
Behavior Genetics the modern field of study concerned with how differences in our genomes contribute to our behavioral differences.
The three principal types of studies in this field are:
Twin studies
Adoption studies
Family studies

9. Twin Studies
Twin studies – comparing monozygotic (identical) twins versus dizygotic (fraternal) twins to determine if criminality is inherited or learned.
Identical twins are genetically identical; fraternal twins share 50% of their genes
Studies focus on the influence of heredity in violent vs. non- violent crimes

10. Twin Studies, Part II
Studies of twins reared together show a correlation between genetics and criminal behavior.
In one Danish study, monozygotic twins were concordant for criminal behavior 52% of the time; dizygotic 22% of the time.
Grove study of twins reared apart showed a high degree of heritability of criminal behavior in monozygotic twins.
Other studies dispute these findings, saying that environment is the most significant factor.

11. Adoption Studies
Studies of children who were adopted have been conducted to examine heredity vs. environment and criminal behavior:
Iowa Study: Compared to a control group, children of incarcerated mothers raised by adoptive parents were more likely to commit crimes as adults.
Denmark Study: Children of fathers convicted of property crimes raised by adoptive parents were more likely to commit property crimes as adults, but no such link for violent crimes.
Sweden Study: Sons of fathers who are both alcoholics and criminal offenders are more likely to be alcoholics and criminal offenders themselves even when raised by adoptive parents.

12. Family Studies
A controversial Dutch study showed that the MAOA neurochemical deficiency (aka “warrior gene”) that is correlated with aggression and impulsivity is hereditary after looking at the males in a large family.

13. Super-Male Syndrome
XYY Syndrome – studies found that males who had an extra male chromosome were unusually tall and predisposed to aggressive and violent behavior
a. 46 chromosomes in most humans
b. Males get an X chromosome from their mothers, a Y chromosome from their fathers.
c. Females get two X chromosomes, one from each parent.
d. Research on prisoners found inmates with a “double Y” chromosome (XYY), referred to as the “super-male syndrome.”