What is complexity?
Consider the molecular makeup of these three objects: an empty room, a lump of carbon, and a guppy.1
The empty room may not look very interesting, but it is actually highly unstable: air molecules are colliding and interacting with each other in all sorts of unpredictable ways. An empty room is chaotic.
Next, think about a lump of carbon. Its molecular movement can be brought almost to a complete stop as its temperature decreases. Chilled carbon is virtually static and unchanging.
Now, think about a guppy. Its molecular structure is much less chaotic than the empty room, but also more active than the lump of carbon. Unlike the room full of air, it is highly ordered and structured—but unlike the lump of carbon, it is neither inanimate nor fully stable. The simple guppy is a complex organism.
Kluger, Jeffrey. (2008). Simplexity: Why Simple Things Become Complex (And How Complex Things Can Be Made Simple). New York: Hyperion pp. 27-29 ↩