by Chi Chi Sileo

About the author: Chi Chi Sileo is a former contributing editor of Insight, a weekly newsmagazine.

In the movie The Bad Seed, a mother reluctantly comes to realize that her angelic-looking little girl is a cold-blooded killer. That was fiction, of course— a story that built on the notion that someone could be “born bad”—and was overly simplistic as an explanation of evil. But new research is suggesting that that notion might be closer to truth than previously believed.

Scientists have begun to ask whether there is something biologically “wrong,” or different, about people who become violent criminals. And they are disclosing intriguing answers. Moreover, they say, criminal behavior can be spotted at a very early age—even as young as 6 years old, the age of the girl...