Steven Pinker, a professor of psychology at Harvard whose forthcoming book, “The Better Angels of Our Nature,” argues that humans have become less violent over the millenniums, suggests that the way to think about genetics and crime is to start with human nature and then look at what causes the switch for a particular trait to be flipped on or off.

“It is not a claim about how John and Bill differ, but about how every male is the same,” he said. Understanding the genetics of violence can “tell you what aspect of the environment you should look at.”

He mentioned one of the biggest risk factors leading to crime: remaining single instead of getting married, a link uncovered by Mr. Laub and Robert J. Sampson, a Harvard sociologist who was a co-winner of the Stockholm Prize. Marriage may serve as a switch that directs male energies toward investing in a family rather than competing with other males, Mr. Pinker said.

Kevin Beaver, an associate professor at Florida State University’s College of Criminology and Criminal Justice, said genetics may account for, say, half of a person’s aggressive behavior, but that 50 percent comprises hundreds or thousands of genes that express themselves differently depending on the environment.

He has tried to measure which circumstances — having delinquent friends, living in a disadvantaged neighborhood — influence whether a predisposition to violence surfaces. After studying twins and siblings, he came up with an astonishing result: In boys not exposed to the risk factors, genetics played no role in any of their violent behavior. The positive environment had prevented the genetic switches — to use Mr. Pinker’s word — that affect aggression from being turned on. In boys with eight or more risk factors, however, genes explained 80 percent of their violence. Their switches had been flipped.

A rash of new research has focused on self-control as well as callousness and a lack of empathy, traits regularly implicated in the decision to commit a crime. Like other personality traits, these are believed to have environmental and genetic components, although the degree of heritability is debated.