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Chimp Fights and Trolley Rides

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First up, we the streets. Join us in Times Square as we poll dozens of people waiting in line to buy discount Broadway tickets. Share in the outrage and mental grunt-work as these thrifty theater-goers try to answer tough moral quandaries. The questions -- which force you to decide between homicidal scenarios -- are the same ones being asked by Dr. Joshua Greene. He'll tell us about using modern brain scanning techniques to take snapshots of the brain as it struggles to resolve these moral conflicts. And he'll describe what he sees in these images: quite literally, a battle taking place in the brain between an "inner chimp" and a calculator-wielding rationale.

Then, we move from inner chimp to outer. Dr. Frans de Waals lets us watch a chimp fight at the Yerkes National Primate Research Center in Atlanta. And we turn our navel-gazing toward the furrier navels of the chimps to learn a little more about this thing called morality: where it comes from, its evolutionary benefit, and why you can't guilt-trip an ape.

Read more:

Joshua Greene: Moral Tribes: Emotion, Reason, and the Gap Between Us and Them

Frans de Waal: The Bonobo and the Atheist: In Search of Humanism Among the Primates

Comments [44]

Wyatt Fehlhaber from Seattle

Scenario 1: "Pulling the lever", is not the same as Scenario 2: "Pushing the guy". The difference is in Scenario 1, you leave out that the man has eyes, ears, and all the same seven senses that we all have. So in pulling the lever we don't kill anyone. If we assume or hope the man can and will jump out of the way at the least minute. If you were in his shoes I bet you would at least try to save your own life, and jump out of the way. Scenario 2 is still Murder. You physically will kill the large man.

Jun. 13 2016 05:52 PM
Leaf from Jackson, WY

My siblings used to create pathways in the 2-3' of snow in the backyard in the winter and play with the pet rabbit and black lab. The dog knew he should not bother the rabbit. One time everyone went inside and forgot to put the rabbit back in his pen. The dog came inside later and was acting strangely all day. He would cower, slink and whine whenever anyone came near him. We never beat the dog, and he had never behaved like this in the past. Everyone kept saying: "what is wrong with the dog?" Later in the day my brother discovered that the rabbit had been slaughtered in the back yard. We assumed that the dogs instincts got the better better of him in the absence of humans to reprimand him. He sure acted like he felt guilty.

Jun. 12 2016 04:33 PM
barbara from Clovis CA

Wanted to offer my solution to the very real possibility of my baby making a sound that would alert the enemy to the location of all in the village. I would cradle my baby and walk out to face the enemy and we would die together and spare those in the village. I agree with those who offered the 3rd solution to the lever pulling and would throw myself on the tracks to stop the train. I always thought a 'hero' sacrificed their life for the many and have seen that in the history of the world.

Jun. 11 2016 04:55 PM
Eileen from Brooklyn, NY

Re-listening to this episode, when the scientists did their experiment observing the lateral frontal poles, did the scientists account for the subjects having children or childless when answering the questions? I wonder if having personal experience would make the subjects decide differently.

May. 17 2016 01:57 PM
Ericka from NY

Jad has kids now! What would he say now?

Dec. 06 2015 06:43 PM

The difference between pulling the lever and pushing the man down is direct vs indirect action. Now think about this: if you stand next to the man on the bridge, I stand below, see the train coming, and shout at you to push the man. If you push him, I would feel as much guilt as pulling the lever, and later on, I would tell you, "Don't feel bad. You did the right thing. You saved 4 people." You, however, wouldn't feel good at all. You have just murdered someone.

If you look through our history, you will see a long list of people who talked other people into killing (some killed millions), but they didn't kill a single person themselves.

Jun. 02 2015 04:44 PM
Jeffrey Weiss from Dallas

Shall we give credit where due? The Trolley Problem has not "been floating around forever." Philippa Foot devised the Trolley Problem in her article "The Problem of Abortion and the Doctrine of the Double Effect" (1967).

Jul. 13 2014 11:19 PM

The two trolley scenarios (pulling the lever vs. pushing the man down) are NOT moral equivalents, contrary to what was expressed in the radio broadcast. I am going along with the game and keeping the assumptions of both scenarios & questions intact. The simple explanation why people respond differently to each scenario is because the physical act is so different. To push a man down with our own bare hands would look, feel, and react differently than pulling a lever. If a computer was responding to each of these scenarios, it could respond that either scenario is "moraly equivelant" because it has no flesh, blood, spirit, feelings, etc. If a person were to see no difference between pulling a lever or pushing a person down, I would probably say that this person was extremely desensitized to violence.

Why couldn't Jad simply say that the brain scan revealed which part of the brain picks up sensitivity to violence, ties to the emotional nerves, or whatever. Instead, the whole program digresses to monkeys & chimps, a fascinating but possibly unrelated topic, scientifically speaking.

Jul. 12 2014 11:40 PM
Jay from NYC

in 1979 Palestinian Terrorists came into a house in the town of Naharia in Northern Israel. The mother was hiding in the attic storage space with her 2 years old baby who was crying. She had to put her hand on the mouth of the baby girl and she died. The mother was the only survivor, as her husband and the 4 years old girls were murdered too.

Jul. 12 2014 10:46 PM
Josh Lobel from Philadelphia, PA

I'm just listening to this for the first time, and I'm wondering if now that Jad has a child he would answer the question about sacrificing his child for the village differently?

Jul. 11 2014 10:27 AM
Samantha Jones from Chicago, IL

The first scenario - where 9 out of 10 people would pull the lever to kill the man but only 1 out of 10 would physically push the man off the bridge themselves - this is the same principal involved with vegetarianism. Forget about the part of the quandary where killing 1 man save 5 others. Rather, focus on the very fact that if people have to physically push a human being off the bridge and do the murdering with their own hands, it is so deeply unconscionable to them that they can't do it. But if they need only pull a lever and watch from a distance as the man is killed, they can do it. This is directly analogous to vegetarianism. If we go to the super market and buy a package of ground round -already processed, wrapped in plastic & resting on a styrofoam container - we can grill it up and eat it without a second thought. Someone else has done the killing. Or more appropriate to the example, someone else has pulled the lever. If we were face to face with the cow that was to be our dinner, it's highly probable that not even 1 out of 10 would choose to do the killing.

Though we are still responsible for the killing, the more we distance ourselves from it the easier it becomes. It is killing nonetheless.

Nov. 18 2013 12:06 AM
melissa from connecticut

I think the specification that the other guy on the bridge was large is supposed to mean he was large enough to stop the train, and I am not, taking the self-sacrifice element out of the equation. They should have made that clearer, if that is the case.

My explanation, which would carry over to the baby question as well, is that the guy on the bridge is perceived as a real human being, not an abstract human life. Neuroscientist/philosopher Josh does not seem to have entertained that possibility.

Nov. 16 2013 04:04 PM
GreenBeanDemon from Hueytown, AL

This \/ down there exactly!
If this is one of those.. Oh well you do not have that option things. Then I will go with pick another situation, as that as no option is so abstracted from the situation, I find myself to distracted by said abstraction decide poop! 8p

Quoted from a post below..............................
Dawn from California
HOW is it possible that NO one has mentioned the real difference between scenerio 1 and 2?
(train track lever vs Train track Push innocent bystander.)

If you assume that the result of pushing a body on the track will stop the train (a big assumption agreed!) then - the actual reason this feels wrong is this: There is another option that is not mentioned.

OPTION #3 - you jump in front of the train yourself! This is why it feels so wrong to PUSH someone else! Why didn't anyone else mention this, it is so clear to me!

Aug. 30 2013 05:51 AM
Kage Kaneshiro from Chicago

We have a quality vs. quantity issue here. It wasn't mentioned so we can only assume. Now assuming those 5 men were a bunch of idiots, because they were not looking out for the train. Perhaps the guy on the other track was the next Einstein, how are we to know? Now would you save Einstein, by killing 5 idiots? Or would you kill Einstein by saving 5 guys? What if the fat guy had a cure for cancer/aids? Would you give that up by sacrificing 5 average Joes? Now who am I to say, we shouldn't even judge whether or not we have the right to control the lives of men. But our government does this all the time, think saving Private Ryan, was it like a whole battalion of men that got wiped out just so that Private F%$#^@%# Ryan can come home to his mommy. Come on!

Oct. 02 2012 10:51 PM

I heard a rebroadcast of this show recently, and seem to remember hearing it a couple of years ago.

The most interesting possibility is that the brain may have more than one way to handle complex decisions. I'd have to say that at this point science can't say much beyond that when it comes to morality and ethics. Morality and ethics are constructs we come up with to try and put some order into personal actions both on an inter-personal level and in larger groups and societies as a whole.

The examples used are totally contrived and meaningless. A little story might give a better example. Locally, a couple of robbers burst into a bank to rob it, killed a guard, and started rounding up the employees. A woman manager grabbed her purse and hid in the closet. When one of the robbers opened the door she used her gun and shot him. She then went into the lobby and shot at the other robber, chasing him out into the street where he was shot and apprehended by the police. Both robbers went to the hospital, and then were convicted and sent to prison.

Did she do the right thing, or should she have put a second bullet in the first robber to make sure he was dead before going to help the other people?

Sep. 01 2012 10:03 PM
Jeff Winchell from Germany

I found it most revealing when they said the proportion of people voting for killing their baby versus not doing this was 50/50. This is the same ratio of people who are Ts or Fs in Myers-Briggs or Jungian personality models. Since scientists have already found brain evidence that describes why Is and Es (Introverts and Extroverts) are different. I imagine they are also getting close to showing brain differences between those who are a "T" and those who are an "F".

May. 31 2011 04:09 PM
Dawn from California

HOW is it possible that NO one has mentioned the real difference between scenerio 1 and 2?
(train track lever vs Train track Push innocent bystander.)

If you assume that the result of pushing a body on the track will stop the train (a big assumption agreed!) then - the actual reason this feels wrong is this: There is another option that is not mentioned.

OPTION #3 - you jump in front of the train yourself! This is why it feels so wrong to PUSH someone else! Why didn't anyone else mention this, it is so clear to me!

Feb. 17 2011 04:19 PM

How fat is the guy? If he is fat enough to stop a train, he probably won't live very long even without the push. Also, he would probably be too big to push. Or if big meant big, as opposed to fat, a guy that big isn't likely to be someone you would push under any circumstances.

Jan. 20 2011 04:49 PM
Byram from los angeles

Interesting way of presenting this. Amazing how resistant we humans are to including our relatives in the concepts behind is because we are also hard wired to prejudice.

This is an interesting animation on the Empathetic Civilization by Jeremy Rifkin and the RSA:

Sep. 19 2010 02:38 PM
Josh Brown from Dayton, OH

HOMESTEAD!!! Please let me know how to find this game! We played that game in 4th grade and I STILL think about it. It is one of my earliest experiences that I distinctly remember having the Machiavelli brought out in me. I NEED to know how to find this game! I have often remembered but have never been able to come up with a name or anything else that would give me hope to find it.

Jul. 15 2010 10:28 AM
Michael from Oceanside, CA

Good discussion here. I agree, the train scenario is compelling at first glance but flawed on second thought.

For you data counters, I personally lean to the notion that unless a person is guilty of actively taking life for selfish gain, I am not justified in playing a hand in their death. No one ought to be on the tracks, let alone not looking around. They ought to suffer the consequences, and I shouldn't make assumptions about what they will or will not do. What if they are expecting to move at the last moment, out of experience? The one on the other tracks would not be expecting the train. He is innocent. As for pushing a man off, he was not involved, and why not throw myself over if we're talking morals! Why was that idea not even mentioned?!

Jul. 11 2010 02:28 AM
Paul Howell from Morro Bay, CA

I tend towards the camp of Florent of Burma. If I had a moment to consider, I think that I would do nothing. Why should I feel guilt or shame about something that isn't my doing or responsibility?

Jul. 09 2010 06:35 PM
Paul Howell from Morro Bay, CA

During this episode, Robert Krulwich makes reference to Moses receiving the 10 commandments as if it actually took place. I find it difficult to fathom how a person can attempt to be intelligent and yet be so superstitious to believe the christian myths as historical events.

Jul. 09 2010 06:28 PM
Toby Saunders from GA, USA

I'm atheist and an ethical-vegan, by the way.

May. 02 2010 06:05 PM
Toby Saunders from GA, USA

I'm not satisfied enough with the train scenario to believe it's an accurate way to measure one's sense of ethics... why would a person in the track stop a train but pulling the lever and making the train switch tracks would not? I wouldn't push the person or pull the lever (I'm the one out of ten) because there are untold factors, like punishment for murder and tampering with a railroad. It's such a flimsy situation!

May. 02 2010 06:02 PM
Heather Burdeaux from Houston, TX

I came to say something similar to the first comment, Lynda's.
The 2 questions being held as parallels is flawed. We do not have the option in the first to personally be hurt. In the 2nd scenario, you can be involved - totally different.

Apr. 17 2010 12:36 PM
Jeff Haynes from Rochester, NY

I'm listening to all the episodes (again) and listening to Jad say to Robert, "I would kill the baby ... you're gonna erase all those people based on your, one, child? ... I couldn't live with myself if I didn't act on behalf of the greater good."

Jad, now that you're a father, the question is no longer abstract. So I'm wondering:

Would you still kill the baby?

Nov. 09 2009 03:12 PM
Jocelyn Brambila from thousand oaks, ca

first, i guess i am the only one but i would neither push nor switch a flick to save five people. The reasoning behind my decision is completely religious. I do not believe i should make the decision between life and death. it is not in my place to alter Gods plan if he believes that five should be killed there is a reason. Not only that, but I could never consciencely kill a person even if im saving others life. By changing the trains path or pushing a person i would be destroying someones life first hand; to me it would be murder.
I can see why most people would have different answers. I do believe that different sides of the brain is used when answering the two questions. most people think rationally when it comes to the first question. when it comes to the second question people are more emotional than.
this was a very interesting clip that makes people think. i truly enjoyed it.

Sep. 09 2009 05:29 PM
Florent from Burma

I asked the question about the lever to my students who are mostly Buddhists. Guess what? About 40% of them said they would not pull the lever. When I listened to the podcast first, I didn't even question the assumption that "hundreds of thousands of people have been questioned by email and 90% of them would pull the lever". It was even mentioned at some point that this is a UNIVERSAL response. This is a very quick shortcut I find. One should not jump to conclusions so quickly. Do the people who have access to internet really represent the majority of people on this planet? I doubt it. The students had a totally different reasoning. If the five guys are on the tracks and are going to die, that's their kamma. If you pull the lever, then you are actively causing the death of that one person, whereas if you don't pull it, you are passively witnessing the death of five people.

Aug. 10 2009 12:25 AM
Mary from Lexington Park, MD

I listened to the rebroadcast of this show and the following thought came to mind-- what would happen if these brainscans were done on people outside of the Western world? People whose cultures carry fundamentally different ideas of death, and more poignantly, of morality? Dualistic thinking (right/wrong, good/bad, which was featured so heavily in the show) has Western roots in Plato and Aristotle, and is totally absent in many Eastern and indigenous cultures. Although these results get us somewhere in a discussion on the biological basis of morality, I am not completely convinced that it's so cut and dry as evolution vs. inner chimp. I would be interested to see some research that spans geography and culture to give a more inclusive perspective on our species.

Mar. 30 2009 12:46 AM
Dave from Minnesota

I also heard the re-broadcast.

I recently heard what a great show this is and this was one the first podcasts that I've listened to. Very disappointing.

I found very disturbing the way the some of the "moral equivalences" were presented as matters of fact - when, in fact, they weren't even close.

Worse yet, this was "backed up" by functional MRI junk science.

The fact that a different part of the brain lit up when considering pushing the fat guy? Did anyone consider that the brain was evaluating whether pushing a human body in front of a trolley would even be able to stop it?

My goodness, this was really claptrap.

Oh, then there was even one of my pet peeves: "I have a theory." It's supposed to be a science show - please don't use the word theory in such a sloppy manner.

Feb. 27 2009 04:21 PM
N.S. Palmer from USA

A fairly interesting discussion that is hampered by over-dramatization and heavy-breathing background music. Perhaps the producers felt that listeners couldn't focus on the program for an hour unless it contained a lot of irrelevant theatrics.

Jan. 25 2009 11:48 AM
Frank Matheson from Salt Lake City

Letting this logic run its course, anyone would feel empowered to kill another based solely on his own assumptions and judgment of what might happen in the future and his own calculations of what represents the greater good. It would put all of our lives at risk at any given time. While this piece was interesting from the perspective of scanned brain activity, it was shallow, morally and intellectually deficient, and frankly, offensive.

Aug. 04 2008 02:30 PM
Frank Matheson from Salt Lake City

In taking the baby's life, the parent is making a series of assumptions, any one of which could be flawed. Based on those series of assumption the parent is taking unto himself the right to kill another human being.

In the case of the train, 5 workers had put themselves at risk by being on the tracks and not paying attention to an incoming train. An individual on another track had placed himself in the same position. The parties are equivalents. Additionally, by pulling the lever to change the tracks you are not precluding any of the individuals from sparing themselves at the last minute, or from the train miraculously coming to a stop.

However, taking the initiative to choose an uninvolved party, throw him over the railing to his certain death is not an equivalent.

Aug. 04 2008 02:29 PM
Frank Matheson from Salt Lake City

This piece was rebroadcast yesterday and while i found it interesting, it was also terribly flawed and disturbing. While there is some merit in looking at brain scans to understand how we are able to respond to a moral dilemma in a split second, without having the time to analyze or understand our reasoning. I was disturbed that the moral dilemmas presented were not explored and in fact represented the choices were presented as logical equivalents. Which they are not.

In the the later case it was presented that taking the baby's life would save the lives of the rest of the village, a logical and justifiable trade-off. In fact, it would merely eliminate the chance that the baby would alert the army to the village's presence. What if the baby were allowed to survive and didn't make a sound? What if the baby were killed and someone else sneezed and the village were was then wiped out? What if the baby made a sound but the army didn't hear it or recognize it? What if the presence of the village were discovered but the army decided to spare part or all of the village. What if the the army did shoot the villagers but the baby somehow survived, hidden among the villagers? what odds would you accept of survival (if it were possible to know) would you kill your child, 10% 20% 50%?

Aug. 04 2008 02:28 PM
Muzz from Evanston, IL

What about a brain scan of a utilitarian?

I would argue that it is moral, thought painful, to push the large man off the bridge. I have serious emotional qualms about that answer, and would probably not actually have the gall to do it in real life.

So I suspect a brain scan of me answering that question would look mostly identical to those who answered no, as we both experience the same emotional revulsion. Our brains look similar, thought we answer differently.


May. 28 2008 03:44 PM

I'm with Gary and Brian on the fat guy and the trolley scenario. I think even those who don't see it obviously, understand that no matter how much you tell people that they can stop the trolley by pushing somebody in its way, no one is going to believe you. You are going to kill six people rather than five if you push him.

May. 08 2008 08:19 PM

I just heard this program (apparently a rerun) today. I had the same thought as Larry. The idea of stopping the train by pushing the guy onto the tracks didn't register with me as a clear way to prevent the deaths of the other five (even though the hypo told me to assume otherwise). I think that plays into the decision subconsciously even for those who think it doesn't.

Jan. 05 2008 01:00 AM
Alex Hayes from Baltimore, MD

Does this idea of chimp morality fly in the face of the judeo-christian concept of original sin?

Jan. 01 2008 08:40 AM
Meghan from Portland, Oregon

First of all, I love Radio Lab. I heard a portion of this episode on 'this american life' and was instantly hooked. I am very much looking forward to the next season... the teasers/podcasts as of late have been great, but at the same time killing me because I can't wait for the next new episodes.

Anyhow, just wanted to say that waiting in line at the grocery store, i noticed time magazine had asked 'what makes us good or evil.' i didn't purchase it but quickly found the section before checking out and just about every question you posed in this section was asked in the magazine... the train one, the baby one etc.

Made me think about the episode and now i must listen to it again.

Thanks for all the good work and good luck with the upcoming season!

Dec. 02 2007 01:42 PM
Bill Andrews from Vienna VA

Thank you for an excellent radio program and podcast. I teach a course on the psychology of combat. I've incorporated this podcast into my course, as a means to consider the biological basis for moral decisions. Thanks for a fascinating program. Some of the ideas I think about are on my personal blog at

Dec. 02 2007 11:36 AM
SJ from Austin, Texas

Let me start by saying that the editor’s choice of going with that sound-clip of the researcher saying that almost no one can say why they chose one scenario over the other was little more than a condescending copout so they could move on through the story about this mystical MRI research.

My take is that even though empathy is strong component of morality, people’s decisions are also guided by their belief in charity, manners, accountability, responsibility, fairness, blood over water, war, death to 'the other' and any number of qualities valued in societies across the globe.

In a scenario where we are powerless to affect any change we feel bad for those on the tracks, but we understand that unfortunate things do happen. Some might question why all of these participants who seem to have experience working around trains would take their complete attention away from a possible disaster with the possibility of paying for their inattention with their lives. But, certain endeavors are risky (like working on or around train tracks) and we can accept the risk taken along with the possible outcomes for those on the tracks.

In a scenario where you are forced to act, either by not pulling the lever or by pulling it, you MUST decide the fate of the workers (1 or many) because you are aware of the events unfolding. But in this situation, one possible assumption is that the people on the tracks put themselves there (active participants), no one outside actor or force moved or pushed them onto the tracks. So, your decision (pulling or not) will impact active participants in a risky endeavor, you just need to decide how many (simple math).

In the final scenario, you’re no longer just choosing how many active participants should be hurt or killed. You are faced with the choice of taking a completely inactive participant in the scene (a bystander) and involving them in the unfolding events in a non-trivial way. This bystander in the scene had nothing to do with the events transpiring and if you don’t push him he may just make it home to live another day.

Whether you gave the respondents the option of physically pushing the man over the bridge railing, or letting them pull a lever from some far away vantage that would wedge him beneath the train, or ‘wishing’ him onto the tracks, or any other contrived scenario, most would still say no because involving an outside participant challenges our sense of ‘fairness’ as they put it.

Jul. 19 2007 09:49 PM
Gary from Germany

Lynda has an interesting point. However, I believe that the problem lies in the question. The way the question set up the first scenario guarantees me that I can save five and kill one by pulling the lever. I know this, because I know the basic design of train tracks. I pull the lever to switch the tracks, the train switches tracks. That's the way trains work.

The second scenario, though, does NOT guarantee that I will save the five by killing one. My knowledge of physics says that there is no person large enough to stop a train (or even a trolley -- the sound effects were a train, though). This tells me that in the second scenario, I am going to kill a person and then see five more killed, as well.

Jul. 13 2007 12:55 PM
Lynda Lambert from Baltimore, MD

I have an answer to your connundrum. The reason why we feel it's ok to pull the lever to "kill one and save five" is because we're not close enough to do anything else, and we hope that the one might get out of the way. When the two men are on the bridge the MORAL thing to do is jump off the bridge in front of the train yourself to save all, except for you. Pushing someone else off the bridge would be actually choosing to save your own life over his; which is immoral. That's why on the bridge it would be murder and pulling the lever is a moral option.

Jul. 08 2007 06:16 PM

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