The possibility of a mandatory life sentence is not an effective crime deterrent. When committing a crime of passion, people seldom pause to calculate the consequences (which explains why even capital punishment does not predict lower state homicide rates). Any deterrence effect comes more from swift and sure arrest. What matters is not the length of a punishment but its probability.

If violent criminal tendencies seldom extend to midlife, and if mandatory life sentences offer little added deterrent effect but considerable financial and social cost, then is it time to rethink life-without-parole sentencing? Will today’s prolonged mass incarceration seem to our grandchildren as merciless and foolish as yesteryear’s debtors’ prison?

Social psychologist Brett Pelham has an answer. In his new book manuscript, Pants on Fire: Evolutionary Psychology, he notes that “Today, the U.S. makes up less than 5% of the earth’s population but about 25% of the earth’s prison population. Arguably, the biggest part of this huge problem is not that we put way too many people in prison. It’s that we keep them there for a very, very long time.”