Searching for the mark of Cain.

MEDFORD, MASSACHUSETTS--Hampered by political, ethical, and methodological problems, a small group of researchers is trying to understand the biological roots of violence. The field has generated some interesting findings and hypotheses about how hormones, genes, and the brain control aggressive behavior. But although the goal is to ultimately find a treatment for violent behavior, researchers emphasize that they are not advocating drugging everybody who has ever committed a crime--or is deemed prone to do so.