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How do schools of fish swim in harmony?

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And how do the tiny cells in your brain[br]give rise to the complex thoughts,

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memories,

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and consciousness that are you?

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Oddly enough, those questions have[br]the same general answer:

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emergence,

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or the spontaneous creation of[br]sophisticated behaviors and functions

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from large groups of simple elements.

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Like many animals, [br]fish stick together in groups,

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but that's not just because[br]they enjoy each other's company.

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It's a matter of survival.

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Schools of fish exhibit [br]complex swarming behaviors

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that help them evade hungry predators,

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while a lone fish is quickly singled out[br]as easy prey.

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So which brilliant fish leader[br]is the one in charge?

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Actually, no one is,

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and everyone is.

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So what does that mean?

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While the school of fish is elegantly[br]twisting, turning, and dodging sharks

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in what looks [br]like deliberate coordination,

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each individual fish is actually[br]just following two basic rules

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that have nothing to do with the shark:

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one, stay close, but not too close[br]to your neighbor,

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and two, keep swimmming.

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As individuals, the fish are focused on[br]the minutiae of these local interactions,

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but if enough fish join the group,[br]something remarkable happens.

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The movement of individual fish [br]is eclipsed by an entirely new entity:

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the school, which has its own[br]unique set of behaviors.

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The school isn't controlled[br]by any single fish.

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It simply emerges if you have enough fish[br]following the right set of local rules.

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It's like an accident that happens over[br]and over again,

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allowing fish all across the ocean[br]to reliably avoid predation.

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And it's not just fish.

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Emergence is a basic property of many[br]complex systems of interacting elements.

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For example, the specific way in which[br]millions of grains of sand

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collide and tumble over each other

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almost always produces the same[br]basic pattern of ripples.

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And when moisture freezes[br]in the atmosphere,

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the specific binding properties[br]of water molecules

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reliably produce radiating lattices[br]that form into beautiful snowflakes.

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What makes emergence so complex

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is that you can't understand it[br]by simply taking it apart,

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like the engine of a car.

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Taking things apart is a good first step[br]to understanding a complex system.

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But if you reduce a school of fish[br]to individuals,

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it loses the ability to evade predators,

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and there's nothing left to study.

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And if you reduce the brain [br]to individual neurons,

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you're left with something that is[br]notoriously unreliable,

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and nothing like how we think and behave,

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at least most of the time.

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Regardless, whatever you're thinking about[br]right now

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isn't reliant on a single neuron[br]lodged in the corner of your brain.

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Rather, the mind emerges from[br]the collective activities

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of many, many neurons.

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There are billions of neurons [br]in the human brain,

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and trillions of connections between[br]all those neurons.

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When you turn such a complicated[br]system like that on,

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it could behave in all sorts[br]of weird ways, but it doesn't.

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The neurons in our brain follow[br]simple rules, just like the fish,

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so that as a group, their activity[br]self-organizes into reliable patterns

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that let you do things [br]like recognize faces,

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successfully repeat the same task[br]over and over again,

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and keep all those silly little habits[br]that everyone likes about you.

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So, what are the simple rules [br]when it comes to the brain?

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The basic function of each neuron[br]in the brain

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is to either excite or inhibit[br]other neurons.

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If you connect a few neurons together[br]into a simple circuit,

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you can generate rhythmic patterns[br]of activity,

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feedback loops that ramp up[br]or shut down a signal,

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coincidence detectors,

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and disinhibition,

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where two inhibitory neurons[br]can actually activate another neuron

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by removing inhibitory brakes.

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As more and more neurons are connected,

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increasingly complex patterns [br]of activity emerge from the network.

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Soon, so many neurons are interacting[br]in so many different ways at once

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that the system becomes chaotic.

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The trajectory of the network's activity[br]cannot be easily explained

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by the simple local circuits[br]described earlier.

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And yet, from this chaos,[br]patterns can emerge,

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and then emerge again and again[br]in a reproducible manner.

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At some point, these emergent[br]patterns of activity

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become sufficiently complex,

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and curious to begin studying[br]their own biological origins,

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not to mention emergence.

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And what we found in emergent phenomena[br]at vastly different scales

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is that same remarkable[br]characteristic as the fish displayed:

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That emergence doesn't require[br]someone or something to be in charge.

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If the right rules are in place,

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and some basic conditions are met,

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a complex system will fall into[br]the same habits over and over again,

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turning chaos into order.

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That's true in the molecular pandemonium[br]that lets your cells function,

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the tangled thicket of neurons[br]that produces your thoughts and identity,

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your network of friends and family,

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all the way up to the structures and[br]economies of our cities across the planet.