Two of his collaborators, George L. Kelling of the Manhattan Institute and John J. DiIulio Jr. of the University of Pennsylvania, have joined with prominent scholars and politicians, including Jeb Bush and Newt Gingrich, in a group called Right on Crime. It advocates more selective incarceration and warns that current policies “have the unintended consequence of hardening nonviolent, low-risk offenders” so that they become “a greater risk to the public than when they entered.”

These views are hardly universal, particularly among elected officials worried about a surge in crime if the prison population shrinks. Prosecutors have resisted attempts to change the system, contending that the strict sentences deter crime and induce suspects to cooperate because the penalties provide the police and prosecutors with so much leverage.

Some of the strongest evidence for the benefit of incarceration came from studies by a University of Chicago economist, Steven D. Levitt, who found that penal policies were a major factor in reducing crime during the 1990s. But as crime continued declining and the prison population kept growing, the returns diminished.

“We know that harsher punishments lead to less crime, but we also know that the millionth prisoner we lock up is a lot less dangerous to society than the first guy we lock up,” Dr. Levitt said. “In the mid-1990s I concluded that the social benefits approximately equaled the costs of incarceration. Today, my guess is that the costs outweigh the benefits at the margins. I think we should be shrinking the prison population by at least one-third.”

Some social scientists argue that the incarceration rate is now so high that the net effect is “crimogenic”: creating more crime over the long term by harming the social fabric in communities and permanently damaging the economic prospects of prisoners as well as their families. Nationally, about one in 40 children have a parent in prison. Among black children, one in 15 have a parent in prison.

Cocaine in the Attic

Ms. George was a young single mother when she first got in trouble with drugs and the law. One of her children was fathered by a crack dealer, Michael Dickey, who went to prison in the early 1990s for drug and firearm offenses.

“When he went away, I was at home with the kids struggling to pay bills,” Ms. George said. “The only way I knew to get money quick was selling crack. I was never a user, but from being around him I pretty much knew how to get it.”