The idea that there is a gene that predisposes its possessors to criminal or aberrant behavior. In the 19th century, Italian physician Cesare Lom-Broso claimed to have identified features that characterized criminals: “the enormous jaws, high cheek bones, prominent superciliary arches, solitary lines in the palms, extreme size of the orbits, handle-shaped ears,” characteristics shared by criminals, savages, and apes, which led them to exhibit “insensibility to pain, extremely acute sight, tattooing, excessive idleness, love of orgies, and the irresponsible craving of evil for its own sake, the desire not only to extinguish life in the victim, but to mutilate the corpse, tear its flesh and drink its blood.”
Modern proponents of the idea that criminality is inherited now focus on genes. Quite recently, researchers testing inmates of a U.S. prison found that there was a higher-than-usual incidence of men carrying an extra Y on the sex chromosome (the female sex chromosome has XX; the normal male sex chromosome, XY). These abnormal individuals had XYY. The claim was then made that the extra Y extra maleness led to criminal tendencies. The motivation of such studies is to identify those individuals with these criminal traits and to persuade or induce them not to reproduce; in this way, the criminal behavior in society will diminish and perhaps eventually disappear. It is one stand of eugenics, the belief that social and medical problems can be bred out. All such claims have eventually been discredited or disproved.