This book is about learning to see ourselves as one entity. It’s about seeing the forest, not the trees. Of course, that could mean a lot of things, so instead of listing all the branches of forestry that this book isn’t about let me tell you a story. In 1958 some couples in Washington, D.C., formed a babysitting co-op. A couple could babysit and thus earn vouchers, which they could later pay to another couple to buy a night out. In effect, the vouchers were a form of money, a scrip. It was a clever idea, but there were problems. For instance, many parents wanted to go out on Saturday nights, but few wanted to sit. To cover such problems, they made up lots of bylaws—seven pages in all. The scheme then tootled along pretty well until 1974, when the co-op’s size ballooned to 150 couples. Suddenly, vouchers were in short supply. Couples didn’t want to spend scrip, afraid that they wouldn’t have any for special occasions. Since no one could earn if no one spent, their little economy seized up. Too many sitters were chasing too few vouchers. A recession resulted. As panic spread, cries of hoarding and shirking filled the air. There was talk of creating a ‘truth squad’ that would grill couples who hadn’t gone out recently. That went nowhere. Then they tried a new bylaw that forced couples to go out at least once every six months. That failed too. Then they flooded the market by creating scrip out of nothing. That worked—but it didn’t last. Over the next couple years they printed so much scrip that soon too many vouchers were chasing too few sitters. The result was budget deficits and inflation.

That story suggests three things. First, we swim in an ocean of tools. Even scrip—and money too—is a tool. It’s just as much a tool as a shovel. Such tools help us do things—in this case, organize ourselves. The story further suggests that we don’t have to be dolts for stuff to go wrong. Many in the co-op were lawyers working for the United States Congress. Some were economists on the level of deputy directors at the United States Treasury. Yet they bungled their own babysitting. But the main point of the story isn’t just that we’re all tool-users, or that we’re all bunglers. It’s that our schemes can fail simply because we’re too used to looking at the trees, not the forest. Often, it’s the forest—that is, our group dynamics—that matters, not our individual intentions, however well-meaning.

For example, you’re driving on a highway and suddenly the cars ahead of you slow down. After a while, they speed up again. Why? Any slowdown on a highway full of fast-moving cars makes a clot of slow-moving cars. So cars entering the clot’s rear slow down. Cars exiting the clot’s front speed up. Thus the clot’s front decays while its rear grows. So it concertinas backward down the road, like a slinky walking itself down a staircase. That clot isn’t like the things we usually think about. It isn’t a single car, nor any particular group of cars. It’s a network effect; something that comes about because of how we affect each other. It’s also self-persistent, despite all our bobbing and weaving and honking.

That clot is like a simple cell that lives on highways. It eats fast-moving cars at its rear and poops slow-moving cars out its front. In a way, it’s like a living thing—it acts in a coherent way, as if designed to do so. It’s made by our actions but none of us controls it, or intends it, or even wants it, yet still it appears to act as if it’s purposeful. An economy is similar—whether it’s a small co-op or the richest nation on earth. Despite our belief that we control it, in many ways it controls us. It’s like a living thing, of which we’re only parts.

If those two examples mean anything, then we collectively needn’t behave as we individually intend. However, our collective needn’t behave randomly either. There are patterns in how we behave even when we don’t intend them. However such large-scale yet unintended patterns are hard for us to see. We tend to focus on individual will—the tree, not the forest.

This book is thus about a new kind of physics—the ‘physics’ of complex networks. To make its ideas concrete, it analyzes our food, jobs, tools, economies, ways of life. It thus discusses oil and water and poverty and slavery and tariffs and women’s rights and bond markets and even the definition of life itself. But its purpose is to figure out our collective, our swarm.

By now you’re probably pretty suspicious. You’re right to worry. We have a word for folks who claim to explain the world with one idea—they’re called cranks. Our swarm can’t explain everything about us. The world is too complicated for that. Plus, we still know very little, so a lot of it is going to change as we learn more. Still, this book may give you some idea of how we fit into something far larger and older than ourselves, and what that might mean for our future.