Is Criminal Behavior Caused by an Extra Y Chromosome?
In 1968, Neilsen et al. reported a study conducted on criminally insane Danish prisoners who had committed arson. Of the 155 prisoners who underwent chromosomal analysis, 2 (1.3%) had the 47-XYY karyotype. As this percentage was 26 to 65 times higher than the percentage of males in the general population with the same extra chromosome, the researchers concluded that men who committed arson also were more likely to have the abnormal karyotype. According to Harris (2005), a similar study was conducted in correctional institutions that housed psychiatric patients. The researchers claimed that those prisons had anywhere from 3 to 20 times more males with an extra Y chromosome than in the general population. Of course, both research studies were based on faulty logic. The researchers did not take a cross-section of the general population and look for the 47-XYY karyotype. Instead, they started with prisoners and then looked for what qualities made them different from the general population.
