EVIL, AGGRESSION, AND CRIMINALITY ARE INTERTWINED AND OFTEN CONFUSED BY LAYPEOPLE AND SCIENTISTS. ALTHOUGH HEREDITARY INFLUENCES ON AGGRESSION HAVE BEEN DEMONSTRATED IN ANIMAL STUDIES, INVESTIGATIONS OF SIMILAR CONTRIBUTIONS TO HUMAN AGGRESSIVITY ARE FREQUENTLY CONFOUNDED BY VALUE JUDGMENTS, CULTURE-BOUND MORALITY, AND SUBJECTIVE ATTITUDES REGARDING RIGHT AND WRONG. ATTEMPTS HAVE BEEN MADE TO SHOW THAT AGGRESSIVITY IN HUMAN BEINGS AS EXHIBITED IN CRIMINAL OR ANTISOCIAL BEHAVIOR, IS INHERITED. STUDIES OF TWINS GENERALLY SHOW A HIGHER RATE OF CONCORDANCE OF CRIMINALITY AMONG MONOZYGOTIC PAIRS THAN AMONG DIZYGOTIC PAIRS. BECAUSE SIBLINGS HAVE BOTH AN ENVIRONMENT AND A PROPORTION OF THEIR GENES IN COMMON HOWEVER, IT IS NOT POSSIBLE TO DISTINGUISH BETWEEN PSYCHOSOCIAL INFLUENCES ON BEHAVIOR AND POSSIBLE BIOLOGICAL INFLUENCES; AS SUCH, THE EVIDENCE DERIVED FROM FAMILY AND TWINS STUDIES IS EQUIVOCAL WITH RESPECT TO DEMONSTRATING A GENETIC INFLUENCE ON CRIMINAL BEHAVIOR. OTHER STUDIES, THOSE FOCUSING ON CHROMOSOMAL ABERRATIONS, INDICATE AN UNUSUAL INCIDENCE OF XYY MALES WITHIN THE POPULATION OF CERTAIN INSTITUTIONS. THE REASONS FOR THE APPARENTLY HIGH RATE OF XYY MALES IN THESE INSTITUTIONS IS UNKNOWN. SOME INVESTIGATORS BELIEVE THAT THESE MEN MAY HAVE SOME NEURAL DEFECT AS A CONSEQUENCE OF THEIR GENETIC MAKEUP; BUT NO CONVINCING EVIDENCE FOR A SPECIFIC DEFECT HAS BEEN ADVANCED AS YET. OTHERS BELIEVE THAT THE FINDINGS MIGHT BE ARTIFICIAL, REFLECTING SAMPLING AND METHODOLOGICAL ANOMALIES. STILL OTHER STUDIES, COMPARING THE RATES OF CRIMINALITY FOR ADOPTED CHILDREN, HAVE FOUND A HIGHER LEVEL OF CRIMINALITY AMONG INDIVIDUALS BORN TO A CRIMINAL PARENT AND GIVEN UP FOR ADOPTION AT AN EARLY AGE. THE HIGHEST RATE OF CRIMINALITY WAS OBSERVED WHEN BOTH THE NATURAL AND ADOPTIVE PARENTS HAD CRIMINAL RECORDS. REFERENCES ARE PROVIDED. (KBL)