362 | Luis Bettencourt on the Universal Properties of Self-Organizing Cities

**SPEAKER_1** (0:00)
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**SPEAKER_2** (1:27)
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**Sean Carroll** (1:57)
Hello, everyone, and welcome to the Mindscape Podcast. I'm your host, Sean Carroll. One of the most vivid thought experiments or metaphors in biology is the idea of replaying the tape of life. This is popularized by Stephen Jay Gould, who had the idea that if you went back to some point in evolutionary history, and I don't think that he used quite these words because he was not a physicist, he was biologist, but if you kept the macro state of the system, so you kept the earth and all the critters on it, but you could change the microscopic features, and then you let the evolution of life go on from that point. Gould argued that you might get very different answers, or at least you could imagine you could get very different answers.
For sure, in the details, that can be true. If an asteroid does or does not hit the earth, the evolution of the dinosaurs would be very different. In fact, we had an episode of Mindscape with my evil twin, Sean B for Biologist Carroll, where he emphasized all of the contingencies and the randomness and how things that you can't control can have a big impact on biology. But there is also an aspect of what you might think of as universality. There are things that are going to happen biologically, whether or not you play the tape once or many, many times. Things like this we've talked about with Jeffrey West, for example, the Santa Fe Institute professor who talks about scaling in biology. The idea that if you think about the mass of different kinds of mammals, let's say, and relate them to their metabolic rates and their lifespans, they all fit on a straight line on a log-log plot, which is to say a power law, a scaling relation, and they can even explain why those power laws are there based on arguments from networks and the geometry of space and things like that.
You can have both and it's really important that you have contingency and you also have laws of physics and constraints from natural reality that lead things to fill certain niches and take certain forms. All of this is to build up to today's podcast with Luis Bettencourt who is actually a collaborator of Jeffrey West, another complex systems theorist who works on cities, not on biology. Probably he's done some biology in his life, but his focus is on cities as complex systems. Like biological organisms, cities are large things made of little things that interact in various ways and have specialization of roles and all this stuff. And guess what?
Much like in biological organisms, cities obey scaling relations. There are certain facts about cities, whether it's the amount of crime that you have or the amount of innovation you have, the new patents or works of art or whatever it is, that are pretty dependably related to the population of the city.
And this is kind of an astonishing fact. I'm speaking to you from Santa Fe, New Mexico, where the Santa Fe Institute is located. Luis is speaking to you on this podcast or will be from Chicago, Illinois, another city I spent a lot of my life in. And when I think about all the cities that I've spent serious time in, Philadelphia, Boston, Los Angeles, Baltimore now, even Santa Barbara and Santa Fe, they're very different. Different histories, different cultures, different people. And yet, if you know the population, you can make very accurate predictions for things like the crime rate, the rate of innovation, the amount of infrastructure you need, et cetera. And amazingly, it's not just the bigger the city. Well, it is true that the bigger city, the more, let's say, patents you have. But it's not if you double the size of the city, you get double the patents. You get more than double the patents. And you can make a prediction for what the scaling relation is, and it comes out to be pretty darn accurate. Not just right now, but even through history and in different countries and so forth. So, to me, this is just the quintessentially beautiful example of why it is useful to think of complex systems as a domain of study all their own. Because very similar kinds of reasoning lead you to insight about both biological organisms and about cities, which are completely different kinds of things. There's something to be said for thinking of the nature of complexity itself and how it shows up in many, many different areas of human interaction, biological interaction, physical instantiations of matter, and all that stuff. By doing it, as we'll see at the end of the podcast, you learn things about how to make better cities and how to move things forward in useful ways. Since most of us in the modern world live in cities, this is relevant to many, many people out there. Let's go.