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Emergence
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The creation of entirely new behavior from assembly of elements who individually lack such behavior.
This is so exciting, important and hard to explain that we revert to a passage from the book "Complexity - The Emerging Science at the Edge of Order and Chaos" by Waldrop, page 82. Bolding is added for emphasis.
"Take water for example. There's nothing very complicated about a water molecule: it's just one big oxygen atom with two little hydrogen atoms stuck to it like Mickey Mouse ears. Its behavior is governed by well-understood equations of atomic physics. But now put a few zillion of those molecules together in the same pot. Suddenly you've got a substance that shimmers and gurgles and sloshes. Those zillions of molecules have collectively acquired a property, liquidity, that none of them possesses alone. In fact, unless you know precisely where and how to look for it, there's nothing in those well-understood equations of atomic physics that even hints at such a property. The liquidity is "emergent".
"In much the same way, says Anderson, emergent properties often produce emergent behaviors. Cool those liquid water molecules down a bit, for example, and at 32 degrees F they will suddenly quit tumbling over one another at random. Instead they will undergo a "phase transition," locking themselves into the orderly crystalline array known as ice. Or if you were to go the other direction and heat the liquid, those same tymbling water molecules will suddenly fly apart and undergo a phase transition into water vapor. Neither phase transition would have any meaning for one molecule alone.
"And so it goes, says Anderson. Weather is an emergent property: take your water vapor out over the Gulf of Mexico and let it interact with sunlight and wind, and it can organize itself into an emergent structure known as a hurricane. Life is an emergent property, the product of DNA molecules and protein molecules and myraid other kinds of molecules, all obeying the laws of chemistry. The mind is an emergent property, the product of several billion neurons obeying the biological laws of the living cell. In fact, as Anderson pointed out in the 1972 paper, you can think of the universe as forming a kind of hierarchy: 'At each level of complexity, entire new properties appear. [And] at each stage, entirely new laws, concepts, and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology, nor is biology applied chemistry.'
"No one reading that 1972 article or talking to its author could have any doubt where his sympathies lay. To Anderson, emergence in all is infinite variety was the most compelling mystery in science. Next to that, quarks seemed so -- boring. That's why he had gone into condensed-matter physics in the first place. It was a wonderland of emergent phenomena."
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Nearly
all significant behavior depends directly on emergence.