Biological heredity and social system, erroneously regarded by some behavioral scientists as an irreconcilable dichotomy, are only two different factors in human behavior, especially in deviance and criminality. Biological criminology and criminal genetics are contributing new insights to the study of criminal behavior and vindicating some of the early criminological theories. While the latter were oversimplistic in using biological determinism as the only explanation of criminality, the latest discoveries in cytogenetics show a definite correlation between abnormal genotypes and aggression in male subjects. In the past, sociological criminologists studied entire families in which criminal behavior was transmitted from generation to generation, theorizing that criminal behavior is learned through family example and perpetuates itself together with the criminogenic conditions that caused it, while continued rejection of these marginal, socially handicapped groups by the mainstream of society isolates them and creates self-reinforcing criminal subcultures. Yet there is mounting evidence that hereditary genetic and physical abnormalities are correlated to aggression and criminal behavior of the most serious and recidivist kind. A recent survey conducted in Italy among an unusually large number of male subjects of varying ages (335, all carriers of the XYY syndrome) confirmed the hypothesized correlation between chromosomal abnormality and violent criminal behavior, even when the presence of the extra Y chromosome was accompanied only by some of the physical traits associated with it (e.g., unusual height) and the IQ of the subjects was average. Of course, biological heredity and genetic determinism are not the only explanations for criminal behavior, a complex phenomenon involving juridical and philosophical considerations and requiring contributions from many disciplines if it is to be realistically evaluated. Italian, French, English, Spanish, and German abstracts are provided. A table summarizes the findings of a survey on the behavior of 335 XYY carriers, and some footnotes contain bibliographic references. --in Italian.