•Studies have suggested that if one MZ twin is a criminal, the other MZ twin is
more likely to be criminal
•DZ twin less likely to display the same criminal tendencies
TWINS CAN BE DOUBLE TROUBLE
•Fail to take into consideration that most monozygotic twins are raised in similar
environments, have similar social experiences
•Because monozygotic twins look so much alike, they are also more likely to
provoke similar responses from other people then dizygotic twins, who may not
look as much alike.
•Study identical (MZ) twins raised by different sets of parents, in different
•Control for social class, child- rearing practices, and diet
•Problem: kids up for adoption are usually lower class, unwanted, poorly fed, etc.
•Problem: adopted kids usually matched with similar-looking parents
•Most adoption studies have found relatively low rate of concordance
•Sacco & Kennedy conclude there is “no real scientific basis for… the existence of
a crime gene”
•Others claim there is measurable degree of association between criminal
behavior of biological parents and their children put up for adoption at birth.
•Examine number, shape, size of chromosomes
•Focus on existence of extra Y chromosome, or XYY gene
•XX chromosome determines gender in women; XY chromosome determines
gender in males.
THE XYY SUPER MALE
•Relatively rare in the general population ( one in 1000)
•More common in prison population (one in 100)
•Impulsive, low tolerance for frustration or anxiety (frequently leave school for this
•Seem fascinated by aggression as indicated by hobbies and sports interest –
often impulsively aggressive
WHERE’S THE BEEF?
•Little evidence to suggest that they commit more violent crimes than other
males, or that they are necessarily more aggressive
•Extreme endomorphic (fat)