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The tragedy unfolded just before sunrise on a mid-April morning in Queens, New York. A man and woman who apparently knew one another fought with increasing venom, and a homeless Guatemalan man named Hugo Alfredo Tale-Yax intervened to help the struggling woman. Her male companion turned on Tale-Yax and stabbed him several times in the torso. For ninety minutes, Tale-Yax lay in a growing pool of his own blood as dozens of passers-by ignored him, took photos, or stared briefly before continuing on their way. By the time firefighters arrived to help, the sun had risen and Tale-Yax had died. 
Tale-Yax's death inspires a predictable stream of responses, beginning with contempt for human nature and ending with questions about how and when humans lost their humanity. Were we better citizens 50 years ago? Or 10 years ago? Does New York attract particularly callous residents, or are good people turned vile after spending too long in the city?
Some of the answers are disturbingly clear. Bystander non-intervention is not merely a product of post-millennial depravity, and similar incidents have been reported as far back as the 1960s. One incident that attracted widespread media attention (and the attention of a couple of brilliant social psychologists) was the stabbing murder of Kitty Genovese, also a Queens resident, in 1964. The details of the attack remain contentious, but the basic facts are disturbing: as Genovese arrived home from work at 3:15am, an assailant stabbed her in full view of at least a dozen apartment residents. None of the residents called the police during the attack, which lasted half an hour, and Genovese ultimately died in the ambulance on her way to the emergency room. The passersby who ignored Tale-Yax behaved just as their counterparts did a half century ago, suggesting that bystander apathy emerged long before 2010.
The effect may not be new, but that doesn't explain why our moral compasses seem to be broken. There are at least two explanations for bystander apathy: either there's something wrong with our moral wiring, or our moral wiring is fine and there's something special about these situations that causes us not to respond. Both explanations attract support. According to psychologist Michael Bradley, interviewed in an ABC story, there is indeed something wrong with our moral wiring: "We have this kind of 24/7 pounding of violence. We now know that that pounding of violence actually causes brain changes where people start to not distinguish between real violence and cyberviolence. We're actually rewiring our brains to not react to violence and pain the way we should." Simply put, it takes a lot for us to respond to violence, because what used to warrant a response no longer registers on our violence-detecting radar. Violent videogames, films, and TV shows have dampened our sensitivity to real life violence, so public stabbings don't register as strongly as they used to.
That explanation sounds plausible, but it neither explains why bystander apathy predates the rise of violent media, nor why researchers have shown that bystanders aren't equally apathetic across different situations. If bystanders are only apathetic sometimes, it seems less likely that our wiring is faulty than that certain situations dampen our tendency to intervene.
The first proponents of the situational explanation were two social psychologists, John Darley (who was also my Ph.D. dissertation advisor) and Bibb Latane. Darley and Latane observed the media storm that followed the Genovese murder, and were convinced that commentators and the media were oversimplifying the story. Instead of blaming New York City or the inherent heartlessness of New Yorkers, Darley and Latane set out to determine whether specific features of the situation may have dissuaded the onlookers from intervening. Their key insight was that the very feature that made the situation so shocking-that there were so many observers and not one of them intervened-ironically explained why the observers were so apathetic in the first place.
To understand their insight, imagine this situation: you and a stranger are stranded on a desert island. Apart from the two of you, there isn't another soul for miles. All of a sudden, the stranger collapses to the sand and lies motionless. How strongly do you feel the need to intervene? If you're like most people, your drive to help the collapsed stranger is overwhelming. It's very difficult to imagine carrying on with your day while your fellow castaway lies unconscious nearby.
Now, imagine a slightly different situation: this time, imagine there are ten of you on the same island. You're all strangers, and none of you is trained as a doctor. Again, one of the other castaways collapses to the sand. Now, how strong is your desire to help? Surely, if you don't help, one of the other castaways will intervene? And what if there were 100 people on the island? Isn't the desire to help even weaker? Ironically, as Darley and Latane observed, the responsibility to help is compelling when you're the only potential source of help, but that same sense of personal responsibility is much weaker when it's divided amongst you and several other potential helpers.
Darley and Latane conducted a series of elegant experiments that demonstrated this diffusion of responsibility principle. In one experiment, students sat in a waiting room and completed a questionnaire before they were due to participate in an experiment in another part of the building. Sometimes, the students sat alone in the waiting room and sometimes they sat with several others. After a few minutes, the experimenters turned on a smoke machine in an adjacent room. Smoke began to filter under the closed door connecting the adjacent room to the room where the students waited for the next phase of their experiment. The waiting room slowly filled with smoke, and the students were compelled to notice that an unexplained source in the adjacent room was producing smoke. Keeping in mind the desert island example, and the fact that numerous passersby ignored Tale-Yax and Genovese, how do you think the students responded?
When the students sat in the room alone, they were quick to leave the room to alert the experimenter to the thickening pall of smoke. But, when they sat with other students, they glanced around nervously at one another and often failed to respond at all. You can imagine the scene: four students attempt to preserve cool detachment as the room becomes so thickly filled with smoke that they can hardly see the questionnaires on their laps. In this and later experiments, Darley and Latane showed that people in groups fail to respond to emergencies, in part because they feel less personal responsibility to help, and in part because they're not sure whether the situation is an emergency at all. It's a classic stale-mate: no one wants to cry "emergency" when there's no emergency at all, so everyone continues to sit coolly by as the room fills with smoke.
Returning to the tragic case of Hugo Tale-Yax, why didn't the bystanders intervene? Perhaps some of the passersby were callous and indifferent-but a surveillance camera nearby suggests more nuanced explanations that make sense in light of Darley and Latane's research. Many of the passersby seemed unsure whether Tale-Yax actually needed help. Since no one else seemed to have intervened, they followed the course taken by the students who sat in the smoke-filled room alongside several other students: they did nothing. Or, perhaps they realized that Tale-Yax needed help, but since there were so many other people in the area, they either assumed that help was on its way, or decided that the responsibility to help wasn't great enough to compel action. Not everyone lives up to Hugo Tale-Yax's heroic and ultimately tragic example; but it seems simplistic to claim that we fail to intervene because our moral wiring has been eroded by graphic videogames and violent movies.
Related media coverage (and thanks to Danny Oppenheimer for pointing out this story):
ABC story with quotes by psychologist Michael Bradley and a catalogue of similar incidents.
Sydney Morning Herald story with embedded video showing footage from the surveillance camera.
Wikipedia article on the Kitty Genovese story.
