In the 1960s and 1970s research scientists conducted dozens of surveys in mental institutions, maximum security hospitals, and prisons across the world. They were looking for chromosomal abnormalities in tall, aggressive men in the hopes that they could link violent crime to a rare genetic disorder that had just been discovered, XYY syndrome.
Although geneticists did find high percentages of XYY men in penal institutions and high security hospitals, much of their research was later questioned.
Many of these XYY men did have a history of crime, but they weren't more violent or aggressive like the researchers had hypothesized. In some of the early studies, the percentages of violent crimes committed by the XYY men were actually less than the control groups they were compared to. In addition, the sample sizes of the observed groups were too small to meet the standards of any credible scientific research.
Of course, news organizations latched onto these studies and sensationalized some of the findings. Many publications used the term "supermale" to describe mass murderers and violent criminals who allegedly had the genetic defect.
Today, most scientists, psychologists and criminologists don't place any value on this outdated research, but the myth of a "supermale" with an extra Y chromosome still lives on in popular culture.
Watch the video above to see how the myth of the XYY "supermale" came to be.