We’ve got a sick orchard, not bad apples


John Havlik (left) and Maura Clement led our experiments on rat bystanders.

Human exceptionalism incurs another blow. In work published today in Science Advances, my laboratory demonstrates the Bystander Effect in rats: rats are less likely to help in the presence of rats who are not helping – confederate rats or as my students love to say, confederats. On the other hand, in the presence of naive rats, who could potentially help, rats are more likely to help than when they are alone, recapitulating recent findings in humans. Thus bystanders either facilitate or antagonize helping depending on their status as naive or confederate. Applied to our human society, this means that people who don’t help are not bad apples; they’re in a sick (confederate) orchard.

One day in 2017, an experiment was born…

Since our introduction of the trapped rat paradigm in 2011, students repeatedly suggested to me that we tackle the bystander effect in rats. I always rebuffed them as I did not immediately know how to make the rat equivalent of human confederates, people who are part of the research team and purposely do not help. Then after a discussion of John Darley and Bibb Latané’s monograph entitled The Unresponsive Bystander: Why doesn’t he help?, John Havlik brought the idea up again. I quickly rebuffed him. But John would not take no for an answer. He read the Latané and Darley book and kept coming back, pushing me to think further. At the time, there was no one else in the lab available to help John run the study. I fell back on, “Okay, but you will have to do the whole thing yourself.” Given that this meant placing four rats from four different cages into one arena within a minute or two and then doing that eight times, I thought I had him. But no. John said, “Fine.” True to his word, he ran the experiment solo in the dog days of August.

The results were so spectacular that the bystander experiments instantly became a focus of my laboratory and more people got involved. Maura Jacobi, then a Pritzker medical student, came on board in the summer of 2018. Rahul Kukreja, a UChicago College student, spent the summer of 2019 running our final bystander experiment using different strains of rats. Yuri Sugano, another UChicago College student, was invaluable in helping me analyze the results and write the paper. Maura’s husband, John Jacobi, got us started with the code for a simulation we ran (see below).

For all of our experiments, we used the paradigm we introduced in 2011 where a rat is trapped in a tube (restrainer) that can only be opened from the outside. A free rat on the outside can then either ignore the trapped rat or help him by opening the restrainer door. Most free rats respond to the distress of the trapped rat, figure out how to open the door (not easy in rat-land) and thereby liberate the trapped rat.

Here are five takeaways from our bystander-work:

#1 Not helping (in the presence of others who don’t help) is being a mammal. It is not a result of the moral decay of society.

The canonical Bystander Effect, hitherto only tested in humans, refers to the lower likelihood that an individual will help in the presence of bystanders than when alone. The paradigm for examining the Bystander Effect has been to use research team members who act as confederates, appearing as subjects but purposely not helping. Psychological experiments on the Bystander Effect have always employed confederates. So we can restate the canonical Bystander Effect as the lower probability of helping when in the presence of confederates than when alone.

To test the canonical Bystander Effect, we made rat versions of confederates by administering midazolam, an anxiolytic similar to Valium. Thereby chilled out, the rats did not help. In the presence of one or two confederats, rats helped very little. And in line with our expectations and with findings in humans, helping was even more antagonized by two confederats than by one.

Rats show the Bystander Effect not because they have reasoned through their role in society or thought about their individual responsibility. They show it because they are good, social mammals and evolution has favored conformity to the actions – or inactions – of other individuals. Darwin would tell us that we are good mammals just as rats are. I would argue that we act as we do because of subcortical affective circuits that closely resemble those in operation in rats.

#2 The presence of other naive individuals facilitates helping.

Compared to one rat alone, duos and trios of naive rats help more. Immediately, this tells us that the canonical Bystander Effect depends entirely on the bystanders being non-helping. When not so specifically instructed, bystanders favor helping. This is in line with results from Philpot et al showing that bystanders intervened in more than 90% of violent street conflicts caught on surveillance video. Philpot et al did not study the likelihood of one person intervening and so strictly speaking, this is not a test of the effect of bystanders (no comparison to solo). But the study does reveal that the likelihood of help being proffered is quite high. Since it is hard to imagine that one lone passerby to a violent conflict would intervene in most instances, the clear conclusion is that naive human bystanders do not suppress helping.

In our study, we were able to take our conclusions one step further and show that naive bystanders actually facilitate helping relative to one rat alone. We did this by making up simulated groups of two or three rats from 48 rats who had been tested alone. In other words, we made in-silica-groups out of control (solo tested) rats. We found that the actual groups helped far more on the first day of testing than did the simulated groups.

This fits with both the Philpot et al results and what sociologists such as Enrico Quarantelli have long established: people help in times of disaster. They do not hesitate or consider the race or gender of the victim. They jump in with others and help, often at great risk to themselves. Our rat results show that the situation does not need to be so dire as life or death.

#3 Bystanders can either degrade or amplify the reward of helping another.

Rats and humans get an internal reward from helping and this reinforces helping. In other words, we feel so warm and good from helping that we help again. We call that reinforcement. And one solo rat is so reinforced by helping once that he helps again on the next day more than 90% of the time. After two days of helping, a rat is more than 99% likely to help on the third day. You get the idea: That felt great. I am going to do it again the first chance I get. Essentially, rats convert to helpers and once converted, they help every day at short latency.

When in the presence of confederats, rats help for the first time on a day and time that is similar to what solo rats do. The difference comes on subsequent days when they don’t help again. Thus, confederats have a chilling effect on helping by antagonizing reinforcement. To put it into human terms, it is as though the perceived indifference of the confederat bystanders makes the rat doubt his own good feeling. These other rats didn’t seem to care yesterday. I guess it was not such a great thing that I did. Not going to do it again.

The presence of naive (competent to help) bystanders amplifies the reward that a helping rat feels. How we figured this out takes a bit of explaining. When we tested trios of naive rats, they all started helping on the first and second day. By day four, it was obvious to John and me that we were not going to learn anything by testing them for the entire twelve days of a typical experiment. The trios had converted and that was that.

Given the futility of learning anything new from further testing, John and I decided to test rats individually on days 7 through 12. Honestly, I have to say that we didn’t have any great plan in mind. It just seemed like a good idea at the time. What a fortuitous decision.

When the rats had been in trios, it was typically the same rat that opened day after day. This is not to say that the others would not have opened but at the very least it was the same rat that beat the others to it on most days. Then when the rats were tested individually we saw that the rats that had been the openers stopped opening. Without their previous audience of two rats, these helpers reverted back to not helping or helping intermittently. This tells us that the audience amplified the reward to an extent that the rat, when on his own, could not match. What is truly remarkable about this result is that rats tested alone are better reinforced than rats tested alone after having had experience with an audience. After the high of the other rats’ approval, helping solo is an enormous come-down.

In sum, if rats are on their own, their own assessment of their actions rules. But in the presence of others, the rats’ perception of the others’ reactions overwrite their own assessment. Sound familiar? I suspect everyone has had the experience of losing enthusiasm for something that others are ho-hum about and getting turbo charged by the excited reactions of others.

#4 Only in-group bystanders matter 

Rahul was the last to came onto Team Bystander. He was interested in how the Bystander Effect would interact with the socially selective effect that we had previously found. In 2014, we showed that rats help strangers but only from strangers of a familiar rat type. In other words, an albino rat who has never met a black-caped rat will not help a black-caped rat. But if an albino rat has lived with one black-caped rat for at least two weeks, then he will help any black-caped rat. This is not some biological basis for for own-race-bias because an albino rat raised with black-caped rats and prevented from ever seeing another albino rat will not help another albino rat (although they do of course help black-caped rats with whom they have lived all their lives).

With that background, let’s return to bystander-land. The setup was an albino trapped rat, an albino free rat, and a black-caped confederat. The only difference between the two groups was that one group of free rats (albino) had never seen a black-caped rat and the other group had lived with one. Those albino rats that were familiar with black-caped rats didn’t help whereas those unfamiliar with black-caped rats helped as though they were solo. In other words, having an unfamiliar type of individual present is the same as being alone. Rats of unfamiliar types are ignored.

This same selectivity is seen in humans. As Mark Levine, Professor of Social Psychology, told Nell Greenfieldboyce of NPR, “We don’t just take any information. We only take information from others we believe to be like us.”

#5 Rats can learn by watching others.

Recall that we only tested trios of naive rats for six days before testing them solo. This was an experimental course correction on the fly, in response to unexpected results. We really did not have time to develop any particular hypothesis, so we went into this with simple curiosity about what would happen. The obvious phenomenon that hit us over the head was that rats switched roles. As I said above, rats that had been helpers in the trios helped much less when solo. And rats that had never helped in the group setting helped when solo. Not only did these rats help, often after never helping over six days, but they did so after only a few minutes. They did not show the typical first-opening lollygagging, getting around to opening the door after twenty minutes or so. They helped within a few minutes. This is an impressive example of observational learning in rats.

What does this all mean for human society?

The effects of bystanders on human helping are perfectly recapitulated in rats. This takes us humans out of the exceptional category (once again) and places us squarely in the regular-mammal category. It is circumstances that determine whether we help or fail to help. In other words, those that don’t help are not bad apples. It is the orchard not the particular apple.

To make this point clearer, let’s look again at the three police officers who stood by and did not help George Floyd as he was being murdered by Derek Chauvin. I think that the current narrative sees these three as three bad apples. I see them as regular members of a confederate institution. It is to be expected that they act in accordance with their intense training and heavily socialization. To break out of that confederacy would take more than simple intention as the case of Alex Kueng, who joined the police force in large part to combat police brutality against black people, illustrates. It takes uncommon grit and conscious fortitude to defy the power of the police confederacy. Take the example of Julius Givens. Despite 22 black police officers having strong feelings of alienation from Lodge 7, only Mr Givens has forged ahead with determination to not join Lodge 7 of the Fraternal Order of Police, a lodge that has no blacks in leadership positions and endorsed Donald Trump, a man widely considered to be deeply racist.

Understanding how we, as mammals, are influenced by our surroundings gives us the informed power to build better institutions. Now would be a good time to take advantage of this opportunity.


  1. Hi ‘#psterlin’, I do think it offers hope; for we ‘can’ foster the emotional intelligence to behave more effectively than rats.
    Our basic species ancestral Enteric Nervous System triggers gut instincts we must not be controlled by, yet it offers sometimes invaluable insights favoured by human evolution. Also, especially in these times, I am keenly aware that, in some ways, rats are better than humans… The learning Professor Peggy and her Team offer inspires the reflection necessary to an emotional intelligence whereby we can transcend limitations of which we were otherwise unaware, uninformed, and therefore powerless to surmount.


  2. Dr. Mason, Thank you for this informative article and your insight into policing issues. I’d be interested in hearing your thoughts about how the police can change their confederate culture to encourage peer action to intervene when use of force becomes excessive. I’ve seen some very small moves, like requiring arrestees to be transported by an officer not involved the apprehension, particularly after a chase or use of force, but I would love to hear your ideas for more sweeping organizational change that recognizes how our brains work. (I’m a retired Police Captain.) How do doctors handle a malpracticing colleague? How do surgeons and operating teams handle it when one medical professional in the room thinks another medical professional is responding inappropriately to an immediate life-threatening emergency? How does the authority hierarchy work? Can a nurse overrule a doctor? Can an intern overrule the Chief of Surgery? Does the medical profession have a good way to interrupt the work of a fellow doctor and demand an instantaneous change in how the work is being done while still retaining the teamwork necessary to perform surgeries going forward? Is there any profession that has a workable means for colleagues to successfully intervene during high stress, dangerous, and time-sensitive activity? I can imagine all the ways these crucial interventions could go wrong, both short and long term, so it would be great if any profession has already figured out how to deal with this human tendency while still maintaining the trust, teamwork, and cooperation necessary in any dangerous vocation that impacts the health and safety of others. Clearly, the police have to find a way to do this, and I hope brain science can help.


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