Forgiveness of others long predates organized religion as a desirable practice.

Michael McCullough, a psychologist at the University of Miami and author of a forthcoming book on the subject, surmises that higher primates and early humans who were more forgiving were more likely to maintain the family and social relations that would help them fend off predators, secure food and go on to reproduce, thereby passing a tendency to forgive on to future generations.

“All critters that make their way through cooperation have to have forgiveness, or the math just doesn’t work out,” McCullough says. “I think people are built to do it.” But when they are taught how to forgive, he adds, they can get better at it.

The impulse is helped along in societies with well-functioning systems of justice. Where courts and prisons can be depended on to mete out punishment or retribution for wrongdoing, individuals find it a little easier to forgive, McCullough says.

Early brain-imaging studies of forgiveness show, too, that this most altruistic of behaviors is not wholly unselfish. In a 2001 study, conducted by psychiatrist Thomas Farrow of the University of Sheffield, England, and published in Neuroreport, volunteers presented with scenarios in which they were asked to forgive others showed strong activity in several parts of the brain.

While forgiving, blood rushed to a part of the prefrontal cortex associated with emotion, problem-solving and complex thought. But it also surged in an area of the brain that weighs reward.

Some people are better at forgiving than others. One of the forgiveness field’s earliest studies, by geneticist Lyndon Eaves, found that twins are alike in their propensity to forgive, suggesting that forgiving attitudes have a strong genetic component.

Psychologist Loren Toussaint of Luther University in Decorah, Iowa, has found that women (who typically outlive men) are more forgiving than men. So are those with higher education. Married people, Toussaint found in a 2002 survey, are more forgiving of themselves and others.