FIERY CUSHMAN: Oh, man, I am so excited to be here. This is my second Welcome Weekend at Harvard because my first one I attended many, many years ago. And I still have friends that I'm in touch with and see at reunions that I met at this weekend so many years ago. 

When I came here, I studied biology. But I kept taking philosophy because I felt like in biology, somehow the questions, they were really interesting. But they were a little bit small for me. In philosophy, the questions were really big and exciting. But it felt like maybe we weren't making as much progress on those questions as I wanted. And then I kind of stumbled into psychology at the very, very end of my time at Harvard, in my senior year. 

And now I teach social psychology. And I start that lecture by trying to explain to students why I've organized my life around studying this thing, why, like, every single morning, I get up. And as soon as I've got the kids at school, I race to the office to study psychology all day long. I come home to cook dinner for the kids. I put them to bed, pull out my laptop, and get right back to psychology again. 

And although the thing that I've studied for the last 15 years or so is mostly moral judgment, and I find moral judgment really interesting, a fascinating part of our psychology, when I teach undergraduates, I start with two slides that are focused on those big, almost philosophy-level questions that are the ones that really get me out of bed in the morning. And these two slides, they can summarize in two pictures the question that I find so motivating. 

So here's the first picture. This is a picture of the world at night, like if you were approaching it from outer space. For the first 3.5 billion years that there was life on Earth, this is kind of what you would have seen from outer space. And then the second picture is the world tonight. So after all of this time of life evolving on Earth, there's one species that so radically transforms everything about what's going on here that if you knew nothing about the planet Earth, and you were coming from outer space, it would be the first thing that you would see. 

And when you got here, it would just be totally clear that there is one kind of life that is doing something way different than all the other kinds of life. And I'm trying to understand how did that happen. What is it that makes us so different from all the other species on Earth? This is a question that people have been asking for a really, really long time. And what I would say in my corner of the literature and my corner of the academic world, people have offered two different types of answers. 

One of them is pretty intuitive. It says, look, we evolved very, very big and powerful brains. They allow us to reason and solve problems. And then the other key thing that we have is culture, which operates a little bit like a gigantic textbook. When people have smart ideas, we pass them on to the people who come after us in a chain. Like, I pass it to you, you pass it to your kids, or the people that you teach in school one day. And so according to this view, most of the heavy lifting is being done by our intellects. 

But culture and social learning, they play a role too, like a textbook does, just getting the information from generation to generation. It seems like that's got to be part of the answer. I mean, there are textbooks, and we do communicate that way. But recently, people have emphasized another very different type of answer, which is that culture is a little bit more like our DNA. Our DNA is modified by random mutations, not by-- we don't have intelligent cells. We don't have intelligent transcription. There's just purely random accidents, but some of them turn out to be useful. 

And because they're successful, they get passed on. People have said, maybe culture works that way too. Maybe we're kidding ourselves thinking that we're coming up with great ideas using our intellect. We're just kind of randomly stumbling into different ways of living, different values, different beliefs. And the people who have good values or good beliefs or useful values, useful beliefs, they're more successful. So they get copied by other people. And it's just like DNA evolving but through social learning. 

I want to give you-- this is a kind of a weird way of thinking. And I'm not sure it's right. I just find it interesting. So I want to give you one of the examples that people in the literature have used to suggest that something like this could be going on. There's many different examples, but the one that I'll talk about is called nixtamalization. So many people who came to the Americas from other parts of the world, the way that we make corn flour and eat corn, we just-- we either eat the corn, or if we want to make corn flour, we dry it out, we grind it up, and we bake with it. 

But if you look at indigenous communities, they do something different. They make masa. They make hominy. These are things that take a lot of work to make. Here's a little schematic of the process called nixtamalization that transforms corn into things like hominy and masa. It has a lot of steps. It's a little bit complicated, not that complicated. Why are they putting all this effort into doing that? 

If you went to ask them, they would say, well, it's a little easier to chew. Or they would just say, like, look, this is the way-- how else would you make a corn tortilla? This is the way that you do it. I want to draw your attention to one particular part of this process, which is counterintuitive. 

See step two-- it says add lime and cook. You might be forgiven that thinking what they're talking about is like the citrus fruit lime. But that's not what they're talking about at all. They're talking about calcium hydroxide. They're talking about a chemical which is very alkaline substance, which actually, if you ate it in a concentrated form, could give you chemical burns. It's not good for you at all. 

These indigenous communities are getting it by burning things, and they take the ash, which has a lot of this-- different alkalines, and especially calcium hydroxide in it. They combine it with the corn. They let it sit for a long time. And then they have to wash it out because it's actually not good for you. And again, they don't have a lot of explanation for why it is that you would want to make your corn products this way. But when scientists went and studied it, they realized that it literally quadruples the nutrient value of corn to do this. 

In particular, it makes available a vitamin B3 which is otherwise absent in the diets of the communities that relied on this practice. And the civilizations that we knew about-- enormous, powerful civilizations in the Americas-- would not have been possible had people not been finding a way to get more nutrient value out of corn than it would have had otherwise. 

But not only are these communities not able to tell you that it's an alkaline substance that unlocks vitamin B3. It might not be surprising to know that that's not the explanation they would give. They wouldn't talk about nutrition at all. They wouldn't tell you this makes it more nutritious or this makes it healthier. They just say this is how you make a tortilla. This is what makes it good. 

And so some people have argued that this should be our basic paradigm for understanding how it is that humans got to where we are today. The thing that makes us so different from other species is just that we copy each other. And the rest is like natural selection. People are just trying different things. And if it works well, if it makes you a little fitter, you have a bigger family, other people copy you. 

So we wanted to explore that in our lab. I teach this stuff in my undergraduate lecture. And a few years ago, there was this student, Danish Bajwa, who kept showing up to my office hours. And we were having fascinating chats together. He thinks he wants to go to law school or become a journalist. I think he should really become a psychologist. I'm still trying to convince him of that. I've got one year left. 

But Danish and I started working on a project together that was a very new and different kind of project for me. But it was exciting because after all of these years studying moral psychology, which I really do love, finally, with Danish, I was doing that research project that felt like it was starting to address the thing that got me up out of bed every morning, like the big questions that I really cared about. 

And recently, I also hired Linas Nasvytis, who will be staying in psychology and going to graduate school at Stanford next year. So the challenge that we face-- because we're experimental psychologists. So what we do is we try to bring interesting things in the world into the lab and run experiments on humans on those things. How are you going to bring nixtamalization into the lab and run experiments on humans? 

It's not easy to figure out how you take a cultural process that takes hundreds of years and generations of people from childhood to adulthood, and then, like, over the course of a weekend reproduce that and play with it in the laboratory. And it took a long time for Danish and I to start to make progress. I don't think you're going to be very impressed with the progress because we're still very much at the beginning of this project. But it's exciting to me. So I want to share it. This is the first version that Danish came up with after really about a year of work that started to reliably work pretty well. 

And it's a very simple idea. There's this character that's you in the middle. And you get to wander around this environment and collect mushrooms. We tell you that you're making a mushroom soup because you belong to a community where people like to eat mushroom soup. The first people who participate in this experiment, that is all we tell them. And they can go around and collect whatever mushrooms they want. 

These people are very confused. They have no idea which mushrooms they're supposed to collect or what the point of this experiment is. But that's OK with us. I'll give you an example of the type of thing that might happen. Oh, I'll tell you. But we don't tell participants. So they don't know this. Only you know this. Those mushrooms are healthy and good, according to us, the experimenters. And these mushrooms are toxic and will kill you. 

But we didn't tell them, and we're not going to tell them. At no point in the entire experiment are we ever going to reveal that. Imagine that they're the kind of toxins that kill you eventually, like after years. But it's not like you taste one, and immediately, you get sick. So you don't know that you're doing a bad thing. 

OK, so people just choose some random path through this environment. They're, like, doing their best to collect these mushrooms. You know, maybe this is like-- you're not feeling great at the end of this trip. But there could be somebody else who does especially poorly. You know, there could be somebody who maybe just through sheer dumb luck, they just happen to think that these mushrooms look a little better than the other ones. 

Remember, there's no red and blue indicating for them. And so this person does really well. So we just collect a ton of data like this. And people are-- some people are having good experiences. Some people are having bad experiences. But then what we do is we decide we're going to kill off all the ones who ate the toxic mushrooms. We're going to assume that they didn't do very well. I mean, maybe they literally died, or maybe they just were a little sickly or they weren't having big families or they weren't as successful in their communities. 

And so when the next generation was born, they're only going to see the people and want to copy the people who did well. OK? So we're going to show a new generation of people the same experiment, but the difference is first we say, I'm just going to show you how a couple of other people in this experiment did this when we gave them the chance. 

We don't say that these were good people. We don't say they were the survivors. We don't say you should copy them. We just say, like, before you do it, we're going to give you a chance to see what some other people did. And then it's going to be your turn. And then we iterate that over and over and over, generation after generation, showing people the strongest survivors. If you've ever studied natural selection, this should feel really familiar. If it works for your DNA, it should work for culture too. 

And that's exactly what we find. On a scale from dead to flourishing, we find that over the course of generations, our population starts to do better and better and better. Now an interesting question we can ask is, what are they saying to themselves and saying to us about why they're doing the things that they're doing? Is it consistent with this idea that they're just adhering to a rigid cultural practice without much thought given to why it is that, in my culture-- microculture that we've created in the lab-- we make soup this way? 

And here's an example of some comments that were consistent with that. These participants are basically telling us, look, I don't know. I just saw some other people do things. It seemed like I should do what they did. So I copied them. That's consistent with the basic model that I presented. But one of the things that popped out to us is that there were also a lot of people who were trying to make sense out of what was happening, who were trying to extract textbook style knowledge. 

They were looking at what other people around them did, and although nobody said to them these ones are poisonous or these ones are healthy, they were trying to make sense out of it. And by trying to make sense out of it, they were actually recovering true facts. It's kind of cool to me that, like, of all the people in this experiment, not a single one was ever told that some are nutritious and some are poisonous. 

But by the end of the experiment, they know that. They figured it out for themselves. In social psychology, which is the field that I sit in, we do think a lot about this process where we find justifications for our behaviors, our cultural practices, and share them with each other. And the predominant view has been to call that rationalization in a kind of a pejorative sense. Like, I hold my values. And now, just to save face or to look good to you, I'm going to construct some reasons post-hoc that make sense out of those values. 

I have no doubt that sometimes rationalization is a kind of pernicious thing, the kind of thing that we should view in through a pejorative lens. But on the other hand, like an experience that I've had is that sometimes if I'm in a conversation with someone about my deeply held values that I learn from others, that I learned from people who came before me, I learn something about why I hold those values by having to explain them to someone else. 

And the things I learned feel true. It feels like what I'm reconstructing is why those are actually pretty reasonable values to hold. And we think on a micro scale, we're starting to pick up on that in this experiment. You can see that in the data as well. We ask people, I know we didn't tell you that any mushrooms were good or any mushrooms were bad. But can you tell me, if you had to guess which mushrooms are good or bad, what would you say? 

And we find that at the beginning of this experiment, people are at chance, where that red bar is. By the end of the experience, they're showing a lot of insight because they're making sense out of their culturally inherited values. 

I should also say that there are some people who just decide to strike off on their own and not do it the culturally inherited way at all. You know, they say things like, hey, wouldn't it be great to have this many mushrooms in a soup? It would be really expensive to have a mushroom soup like this in real life. I hope these mushrooms are non-toxic. 

Obviously, these people all died in our experiment. It emphasizes to me-- you know, to come back to this big picture theme, you all know Newton's quote. Newton famously said, "If I've seen farther than others--" you know, in inventing physics and calculus-- "it's by standing on the shoulders of giants." And for me, it's fun to be able to take that phenomenon, that standing on the shoulders of giants phenomenon that makes us so different than all other species, and to bring it under experimental control and to begin to be able to play with it. 

I will also just share with you that my own experience at Harvard is one where I do feel incredibly lucky to be able to stand on the shoulders of, for instance, the kinds of speakers that you just heard from this morning, where every once in a while, you get that feeling like you're seeing just a little bit further than other people have seen in some direction or another. 

But the thing that I most love about Harvard that I think Newton actually didn't capture-- I love finding people like Danish around me and hoisting them up on my shoulders and then getting a perspective on the world that I never, never would have had otherwise if I hadn't had their help looking in a direction that I've never looked before. So thanks very much. Enjoy your time here.