The XYY chromosome affair

The XYY chromosome episode may have been the most publicized criminological event of the century. Males usually have 46 chromosomes; two of these are the sex chromosomes, one X and one Y. (XY is the notation for this configuration.) The normal female sex chromosomes are XX; the male sex chromosome is Y. In 1961 Sandberg, Koeph, Ishihara, and Hauschka found a man with an extra Y chromosome (XYY). This man was not especially aggressive or criminal, but, to some, the extra male chromosome suggested the possibility of exaggerated maleness, aggressiveness, and violence. Indeed, following this discovery, chromosome surveys were undertaken in some institutions for the criminally insane, and the results seemed to suggest that XYY men were exceptionally violent. The press presented descriptions of the crimes perpetrated by some of these men that could have furnished material for a series of lurid horror films. The popular press (and some scientific publications) began to develop an image of a huge hulk of supermaleness, spurred on to aggressive, violent acts by his extra Y chromosome.

I am describing this phenomenon of the late 1960s and 1970s because it is an outstanding example of a specific biological factor being linked causally to criminal behavior. The reaction of some social scientists to this suggestion of a biological basis for criminal behavior was instructive. In 1970, two responses were published. Kessler and Moos (1970) dispassionately and incisively surveyed the literature and noted that the mental hospital findings were quite inconsistent.