WHY WE Walk On By

With apologies to Dickens, let’s call these Two Tales of One City, unfolding within the span of a single week last September. In one, dozens of onlookers do nothing (except film the horror with their cellphones) while at least seven assailants stab a 16-year-old boy to death in broad daylight in the New York City suburb of Oceanside. In the other, two onlookers jump onto a subway track in the Bronx to save a 5-year-old girl whose father had jumped in front of an oncoming train with her in his arms. He died, she lived. The Good Samaritans knew neither the father nor the girl nor each other.

For half a century psychologists have wrestled with what they call the bystander effect. Although the phenomenon is almost certainly timeless, as a