This chapter is the first of two concerning the possibility that, with all social and learning factors held constant, some individuals are more likely to become criminals than others. It considers the genetio inheritance of criminal behavior by means of data on the anatomical correlates of crime, sex differences, chromosomal anomalies, family, adoption, and twin studies.

The main purpose of research in this area is to separate out fully the influences of biological inheritance from those of the post-natal environment. As will be seen, all methods fall short of this target, essentially because the requisite degree of experimental control is rarely, if ever, obtainable. But something remains, sufficient to keep alive the possibility that biological factors play a more than trivial role in the criminal behavior of at least some offenders.

Anatomical correlates

The quotation from Julius Caesar which heads this chapter embodies a very old belief, which antedates Shakespeare by at least 3,500 years. It is found in Egyptian writings, in Homer's epics, in the Hippocratic and Galenic doctrines of medicine, and in the Bible. A law of medieval England stated: “If two persons fell under suspicion of crime, the uglier or more deformed was to be regarded as more probably guilty” (Ellis 1914, cited by Wilson and Herrnstein 1985, p. 71).