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.
游動的魚群如何保持協調性? 你腦中那些微小的細胞, 又是如何產生複雜的思想、 記憶 與意識,而形成「你」? 令人驚奇的是, 這些問題有著共通的答案: 突現 (emergence) 也就是由一大群的基本單體 所自發產生的複雜行為與能力 和許多動物一樣,魚聚集形成群體 但那不是因為牠們喜歡陪伴彼此 而是攸關存活 魚群可以展現複雜的群體行為 幫助牠們迴避飢餓的獵食者 落單的魚則會 被迅速鎖定為易捕食的獵物 所以哪隻聰明的魚領袖 負責引導大家? 實際上,沒有一隻魚是 大家都是 這意味著什麼? 當魚群優雅地迴旋、旋轉, 巧妙地避開鯊魚 顯現出深思熟慮後的協調性 每一隻魚本身其實 都只遵守兩個基本原則 跟鯊魚一點關係也沒有 第一點:保持緊密,但也不要太靠近你鄰居 第二點:一直游 作為一個個體,魚們專注在 自己區域間互動的細節 但如果加入群體的魚夠多, 神奇的事情就會發生 單一隻魚的動作 被全新的龐大群體所掩蓋 魚群,擁有它獨特的行為模式 魚群,不被任何單一隻魚控制 只要有夠多魚遵循一定的自身原則, 魚群就出現了 就像是一再出現的意外 使全海洋的魚群能安然避開獵食者 不只魚會如此 「突現」是許多複雜系統中 單體互動的基本性質 舉例來說,數百萬沙粒以獨特的方式 彼此之間碰撞、翻滾 幾乎總是會產生相同基本型態的波紋 而當水氣在大氣中凝固 水分子間特定的連結方式 一致產生放射狀晶格, 形成美麗的雪花 「突現」會顯得複雜 是因為你無法將它拆成 一小塊一小塊來理解 就像汽車引擎 將事物拆解 是了解複雜系統的第一步 但如果你把魚群拆成單一隻魚 牠就失去了躲避獵食者的能力 也就沒什麼好研究的了 而如果你把大腦拆成單一個神經元 你只會剩下極不可靠的資訊 一點也不像我們 思考或做出行為的方式 至少大多時候如此 無論如何,你此刻所想的事情 並非起源於你腦中的單一神經元 相反地,思想由許多神經元 共同活化而產生 人類大腦中有數十億個神經元 這些神經元間有著數兆的連結 當你啟動這麼複雜的系統 它很有可能以各種 奇怪的方式呈現,但它沒有 我們腦中的神經元 遵守簡單的規則,就像魚群 所以群體的動作 自我組織成可信賴的模式 使你可以辨識人臉、 成功地一再重複相同任務、 以及保持令人喜愛的呆萌習慣 所以,大腦中的簡單規則是什麼? 大腦中每一個神經元的基本功能 是要活化或抑制其他神經元 如果你將一些神經元 集合成一個簡單迴路 你能產生一個有節律的活動模式 回饋迴圈會增加或停止信號、 共同探測器, 和去抑制 兩個抑制性神經元可以藉由移除 抑制性阻礙物,活化另一個神經元 當連結的神經元越來越多 網絡便能產生更多複雜的行為模式 很快地,許多神經元同時 用許多不同的方式互動 使得系統變得混亂 神經網路的活動軌跡無法只用 先前說的簡易區域迴圈解釋 而且,即便一團混亂,仍能產生規律 並以可重複的方式一再呈現 某些時刻,這些突現的活動模式 變得足夠複雜 還會因為好奇 而開始研究自己的生物起源 更遑論突現現象 我們觀察到許多截然不同的突現現象 就跟魚群展現的優越特性一樣: 突現無須某人或某物來指揮 只要規則已制定 基本條件被滿足 複雜的系統 就會一再陷入相同的慣性模式 亂而有序 事實是分子們亂舞 讓你的細胞發揮功能 神經元糾結 讓你的思想與個性顯現 你與朋友、家人的社交網絡 這一切造就了這個星球上 眾多城市的結構與經濟