Twin Studies and Adoption Studies

1
Twin Studies and Adoption Studies

• I get it from my parents

2
XYY

• Biology
• Genetics
• Social Behavior

3
Environment

• Genetic predisposition and never commit a
  criminal act
• Lack of a genetic predisposition and be a criminal

4
How Can we Determine the Extent of Criminal
Behavior is Genetically Influenced?

• TWIN STUDIES
• ADOPTION STUDIES

5
Twins

• Monozygotic Twins
• Single Egg
• Dizygotic Twins
• Separate Eggs
• Share about half the genes

6
Johannes Lange(1920s)

• 30 Pairs of Same sex twins
• 13 Identical 17 Fraternal Pairs
• One Member of Each Pair was a known criminal

7
Twin Studies Result ( Lange 1920)

• 13 Identical Twins
• 10 Pairs Both Twins Were Criminal

8
Twin Studies Result ( Lange 1920)

• 17 Pairs of Fraternal Twins
• 2 Pairs Were Criminal

9
Karl Christianson and Sarnoff A. Mednick
1881-1910 Study

• 3586 pairs of twins
• Listed Serious Offenses only

10
Mednick and Christiansen

• Identical Twins If one is criminal, the other
  is likely to be criminal by 50
• Fraternal Twins If one criminal and the same sex
  as the other, the other has a 20 likelihood of
  being criminal.

11
David C. Rowe, D. Wayne Osgood

• Recent American Study
• Supported the Findings of Christiansen and Mednick

12
Adoption Studies

• Best way to separate the Inherited Traits from
  Environmental Conditions
• Largest Study was in Denmark 1924-1927 by Sarnoff
  A. Mednick
• 14,427 Male and Female Adoptions
• Felony Cases Only

13

• If the Biological Parents were not Criminal and
  the Adoptive Parents Were not Criminal, What
  Percent of the Offspring were Criminal?

14

• 13.5 Criminal

15

• If the Adoptive Parents were Criminal and the
  Biological Parents were not Criminal?

16

• 14.7 Criminal

17
If the Adoptive Parents were Non Criminal and the
Biological Parents were Criminal?
18
20 Crime Conviction of the Offspring
19
How About Both Sets of Parents Criminal?
20

• 24.5

21
Does this Data Suggest that Criminality is
Inherited?
22
How About Females?

• Study of 862 Adopted Males
• 913 Adopted Females

23

• Who Do You Think Gets More Criminal Tendencies
  Biologically Males or Females?

24

• Studies Show that Females Inherit Criminal
  Tendencies More than Males

25
Are Violent Tendencies Inherited?

• No one has ever found evidence of inheritance of
  violence.
• Mednick