So, humans are actu­al­ly remark­ably averse to per­form­ing harm­ful actions. And para­dox­i­cal­ly, one of the best exam­ples of this is war. After the Battle of Gettysburg, 27,500 mus­kets were recov­ered. And the US Army expect­ed to find almost all of them emp­ty. Because what sol­diers were trained to do is to load a car­tridge in the rifle and then as soon as they had it loaded, point it at the ene­my and shoot. But when the Army ana­lyzed the the mus­kets that were col­lect­ed, what they found is only about 15% of them were emp­ty. And maybe 45% or so were loaded with one car­tridge. But amaz­ing­ly, almost a quar­ter were loaded with two car­tridges, one right on top of the oth­er. And the remain­ing quar­ter or so were loaded with three or even more. Sometimes up to twen­ty car­tridges stacked one on top of the other.

And when the Army tried to fig­ure out what was going on, what they real­ized was that the sol­diers were load­ing, they were try­ing to shoot but they could­n’t pull the trig­ger. So they would pre­tend. And then they would load again, and pre­tend again, until final­ly some­body shot them.

So, for the US mil­i­tary, they con­sid­er this an enor­mous prob­lem and you can under­stand why. It hap­pens in con­flict after con­flict. It’s not just the Civil War. Front line GIs are real­ly resis­tant to killing. But from my per­spec­tive, I hope from yours too, you don’t see this as a prob­lem but an extra­or­di­nary oppor­tu­ni­ty to try to under­stand the emo­tion­al mech­a­nisms that pre­vent humans from doing harm to each oth­er, but also to under­stand their limitations. 

So in my lab we’ve been doing a lot of work on this. One of the most recent par­a­digms that we’ve used to try to get this under exper­i­men­tal con­trol is to ask peo­ple to act out pre­tend harm­ful actions. So for instance, we’ll give them a dis­abled hand­gun. We’ll show them that it’s fake. That it could­n’t pos­si­bly harm a fly. We put it in their hands and then we ask them to shoot us in the head. Actually, most of the time it’s my grad­u­ate student. 

So then what we do, we have them hooked up to to mea­sure­ment devices that record their blood pres­sure, heart rate, so on and so forth. And those are reli­able indi­ca­tors of a kind of aver­sive emo­tion­al response. And we find that even for a total­ly pre­tend behav­ior, peo­ple have a real­ly dra­mat­ic emo­tion­al response to this.

But inter­est­ing­ly, if we ask them to just watch as one grad­u­ate stu­dent shoots anoth­er grad­u­ate stu­dent, the response is sig­nif­i­cant­ly weak­er. And this teach­es us some­thing real­ly impor­tant about the nature of our aver­sion to harm. So, naïve­ly you might think that the rea­son that we don’t like to shoot a gun is because we don’t like the out­come. We don’t like the fact that it’s going to kill a per­son. But even though that’s almost cer­tain­ly true, it could­n’t pos­si­bly explain the data that I showed you, because first of all peo­ple knew that there was no actu­al harm that was going to occur. And sec­ond of all, if they’d been wor­ried about even an imag­ined out­come, they should’ve been just as wor­ried when they were wit­ness­ing as when they were doing it themselves.

So what it looks like is part of our aver­sion to harm is real­ly just an aver­sion to the phys­i­cal action. It’s an aver­sion to feel­ing the weight of the met­al in your hand and wrap­ping your fin­ger around the trig­ger. In a follow-up study, we cre­at­ed a new ver­sion of this where instead of hav­ing peo­ple pull the trig­ger with their own fin­ger, we just tied a six-inch rope around and had them pull the rope. And under those con­di­tions, you find that the emo­tion­al response dropped by almost half. And this is real­ly real­ly sig­nif­i­cant in an era when bat­tle­field tech­nolo­gies are chang­ing the types of phys­i­cal actions that sol­diers are called upon to per­form, in ways mak­ing them much more dis­tant from their vic­tims. But I think equal­ly impor­tant­ly in oth­er ways bring­ing them much much clos­er to their victims. 

And this isn’t just a mat­ter of war, either. I mean, all of you have tech­nol­o­gy in your pock­ets that in ways make you much much more dis­tant from peo­ple, and in equal­ly impor­tant ways bring us much clos­er togeth­er. And this rais­es deep ques­tions for how you’d want to design and use that type of technology.

But for me per­son­al­ly, what’s most excit­ing about this research is that all around the world I have col­leagues who are mak­ing great strides in under­stand­ing human learn­ing. The neur­al and a com­pu­ta­tion­al mech­a­nisms that trans­late the expe­ri­ences that we under­go into the behav­iors that we per­form. And in my lab we’re try­ing to take these mod­els and use them to under­stand moral behav­ior. And so this presents us with a real­ly big ques­tion. And this isn’t just a ques­tion for me or for my lab but for the whole field of moral psy­chol­o­gy. Which is, as we gain a bet­ter sci­en­tif­ic under­stand­ing of human morals, is it pos­si­ble that we can actu­al­ly over­come some of its limitations?

Thank you very much.