Viewpoint: Yes, the best studies of XYY males indicate that they are more prone to aggressive behavior than XY males.

Viewpoint: No, the presence of the extra Y chromosome in XYY males does not in and of itself produce aggressive behavior in those affected; dealing with aspects of the condition during adolescence is a more likely explanation for any later social difficulties experienced by XYY males.

The debate about the XYY karyotype can be seen as part of the old debate about nature and nurture. The belief that nature, or biological determinism and inheritance, is more important than environment and education was the basis of the field that Francis Galton (1822-1911) called "eugenics." According to Galton, talent, character, intellect, disposition, and other aspects of "natural ability," as well...