Everyday Examples

Bird flock
A flock of birds hundreds strong wheeling in perfect synchrony overhead is one of nature's great sights. If a single bird fell out of line, utter confusion could ensue, yet none does. Harmony reigns, spawning a behavior (flocking, with its swift motion and sudden course changes) that is not predictable from knowing all there is to know about any single bird. Flocking "emerges" from simple rules instinctively followed by each bird: keep a precise distance away from and stay aligned with your nearest neighbors, and avoid predators. The "wave" in a stadium operates along similar lines (minus the predator part).

Ant colony
Ants are not mental giants, and they can't see the big picture. Yet out of their simple behaviors—follow the strongest pheromone trail, say, or save the queen at all costs when under attack—arises a classic example of emergence: the ant colony. The colony exhibits an extraordinary ability to explore and exploit its surroundings. It is aware of and reacts to food sources, floods, enemies, and other phenomena, over a substantial piece of ground. Each ant dies after days or months, but the colony survives for years, becoming more stable and organized over time.

Slime mold
Turn over a rotting log in a forest and you might see a fungus-like blob coating a patch of the decomposing wood. Return the next day and it might have vanished. Where did it go? Nowhere. It is Dictyostelium discoideum, the slime mold. For most of its life, the slime mold exists as thousands of single-celled organisms, invisible to the naked eye as they dine on decaying leaves and wood. But when weather conditions become less than ideal, those cells band together, forming a single entity—"they" become an "it." If you used time-lapse photography, you could actually see the macroorganism crawl along, slow as a starfish.

Water
A molecule of water is as basic as it gets—just an oxygen atom with two hydrogen atoms adhering to it. But throw a jillion of them together, and voilà, you get a substance with characteristics that the individual molecules do not possess on their own—liquidity, for instance. Emergent properties often beget emergent behaviors, and those of water are no exception. Cool water down enough and it becomes a solid, for instance; warm it up enough and it becomes a gas.

Hurricane
Take a small atmospheric disturbance whirling around in a stretch of warm tropical ocean, at least 80°F. Make sure it's 300 miles or more from the equator so it's sufficiently stirred by the Earth's rotation. Season it with evaporating seawater, which condenses when it rises high enough into the atmosphere. Lower the atmospheric pressure near the surface. What do you get? The emergent happening known as a hurricane, with its emergent attributes (e.g., winds of at least 74 miles per hour) and its emergent behaviors (e.g., an ability to suddenly alter course).

City
Cities have a remarkable ability to self-organize as they grow. Neighborhoods of like-minded people and similar kinds of businesses establish themselves organically, from the bottom up. Thus, New York gained Chinatown and Little Italy, the Garment District and the Flower District, enclaves that appeared regardless of such top-down forces as planning commissions and zoning laws. Such communities-within-the-community emerge on their own, lending cities their distinctive personalities.

Stock market
In the 17th century, the economist Adam Smith described an "invisible hand" that guides markets to produce just the amount and variety of goods that the public needs. The stock market has its own "invisible hand." The purely self-interested actions of thousands of buyers and sellers result in the purely blind workings of the stock market—the sudden shifts in activity and valuations, the bubbles and crashes—as well as the market's notorious properties of stupendous intricacy and frustrating unpredictability.

Chess
There's hardly a better example of emergence than chess. Out of a game with fewer than two dozen rules comes complexity to challenge the greatest minds on Earth. As the emergence expert John Holland notes, if you have a game that ends after 50 moves and offers 10 possible moves from any configuration along the way—a length of game and number of options roughly equivalent to that found in chess—you will have 10⁵⁰ ways of playing the game, "a number," he says, "which substantially exceeds the number of atoms in the whole of our planet Earth."

Consciousness
For some experts, the mind is the ultimate exemplar of emergence. Your brain contains several billion neurons that perform a very simple function: relaying electrical messages across synapses to their neighbors. It's a physical action, yet out of their collective firings somehow arises a psychological phenomenon—the conscious mind. Can consciousness be reduced to the interactions of neurons? Experts have no way of knowing, because the brain is orders of magnitude more complex than any computer today, making answering that question at present difficult if not impossible.

Life
Are you an emergent phenomenon? Consider this: At any given time, some 75 trillion cells are doing their thing in your body. But they are constantly dying and being replaced by new ones, such that in less than two years you won't have a single cell you have today. Yet you remain you. How is this possible? Even though each of your cells contains your entire genome, you would hardly say that any one of your cells constitutes you. But taken together they amount to you. Life, says the theoretical biologist Stuart Kauffman, is indeed an emergent event.