In an interesting review of Paul Bloom’s book Just Babies: The Origins of Good and Evil, Michael Shermer finds where humans learn to solve complex moral dilemmas, such as this one pitting helping vs. hurting, rescue vs. revenge:

On the platform of a subway station, a woman and two men are talking a few feet away from the open track pit. Without warning, one of the men shoves the woman. She staggers backward toward the edge. The other man reaches out to catch her, but he is too late, and down she goes onto the tracks. In an instant, he reacts. He turns on his heels and coldcocks the culprit. It is a magnificent roundhouse to the face that snaps the wrongdoer’s head back. Satisfied with this act of revenge, he turns, hesitates and dashes over to pull the woman to safety. He reassures her, then takes off after the malefactor, who has beat a hasty retreat.

 

As Shermer describes Bloom’s work, it’s clear that morality is learned very early in life:

In Bloom’s laboratory, a one-year-old baby watched puppets enact a morality play. One puppet rolled a ball to a second puppet, who passed the ball back. The first puppet then rolled the ball to a different puppet, who ran off with the ball. The baby was next given a choice between taking a treat away from the “nice” puppet or the “naughty” one. As Bloom predicted, the infant removed the treat from the naughty puppet—which is what most babies do in this experiment. But for this little moralist, removing a positive reinforcement (the treat) was not enough. “The boy then leaned over and smacked this puppet on the head,” Bloom recounts. In his inchoate moral mind, punishment was called for.

 

Read the rest of Michael Shermer’s article from Scientific American here.