Nathan S. Jacobs: How do schools of fish swim in harmony?

How do schools of fish swim in harmony? And how do the tiny cells in your brain give rise to the complex thoughts, memories, and consciousness that are you? Oddly enough, those questions have the same general answer: emergence, or the spontaneous creation of sophisticated behaviors and functions from large groups of simple elements. Like many animals, fish stick together in groups, but that's not just because they enjoy each other's company. It's a matter of survival. Schools of fish exhibit complex swarming behaviors that help them evade hungry predators, while a lone fish is quickly singled out as easy prey. So which brilliant fish leader is the one in charge? Actually, no one is, and everyone is. So what does that mean? While the school of fish is elegantly twisting, turning, and dodging sharks in what looks like deliberate coordination, each individual fish is actually just following two basic rules that have nothing to do with the shark: one, stay close, but not too close to your neighbor, and two, keep swimmming. As individuals, the fish are focused on the minutiae of these local interactions, but if enough fish join the group, something remarkable happens. The movement of individual fish is eclipsed by an entirely new entity: the school, which has its own unique set of behaviors. The school isn't controlled by any single fish. It simply emerges if you have enough fish following the right set of local rules. It's like an accident that happens over and over again, allowing fish all across the ocean to reliably avoid predation. And it's not just fish. Emergence is a basic property of many complex systems of interacting elements. For example, the specific way in which millions of grains of sand collide and tumble over each other almost always produces the same basic pattern of ripples. And when moisture freezes in the atmosphere, the specific binding properties of water molecules reliably produce radiating lattices that form into beautiful snowflakes. What makes emergence so complex is that you can't understand it by simply taking it apart, like the engine of a car. Taking things apart is a good first step to understanding a complex system. But if you reduce a school of fish to individuals, it loses the ability to evade predators, and there's nothing left to study. And if you reduce the brain to individual neurons, you're left with something that is notoriously unreliable, and nothing like how we think and behave, at least most of the time. Regardless, whatever you're thinking about right now isn't reliant on a single neuron lodged in the corner of your brain. Rather, the mind emerges from the collective activities of many, many neurons. There are billions of neurons in the human brain, and trillions of connections between all those neurons. When you turn such a complicated system like that on, it could behave in all sorts of weird ways, but it doesn't. The neurons in our brain follow simple rules, just like the fish, so that as a group, their activity self-organizes into reliable patterns that let you do things like recognize faces, successfully repeat the same task over and over again, and keep all those silly little habits that everyone likes about you. So, what are the simple rules when it comes to the brain? The basic function of each neuron in the brain is to either excite or inhibit other neurons. If you connect a few neurons together into a simple circuit, you can generate rhythmic patterns of activity, feedback loops that ramp up or shut down a signal, coincidence detectors, and disinhibition, where two inhibitory neurons can actually activate another neuron by removing inhibitory brakes. As more and more neurons are connected, increasingly complex patterns of activity emerge from the network. Soon, so many neurons are interacting in so many different ways at once that the system becomes chaotic. The trajectory of the network's activity cannot be easily explained by the simple local circuits described earlier. And yet, from this chaos, patterns can emerge, and then emerge again and again in a reproducible manner. At some point, these emergent patterns of activity become sufficiently complex, and curious to begin studying their own biological origins, not to mention emergence. And what we found in emergent phenomena at vastly different scales is that same remarkable characteristic as the fish displayed: That emergence doesn't require someone or something to be in charge. If the right rules are in place, and some basic conditions are met, a complex system will fall into the same habits over and over again, turning chaos into order. That's true in the molecular pandemonium that lets your cells function, the tangled thicket of neurons that produces your thoughts and identity, your network of friends and family, all the way up to the structures and economies of our cities across the planet.