What's In a Name

A classic example of emergence lies in the flocking behaviour of birds. A computer simulation can use as few as three simple rules (along the lines of, "Don't run into each other.") and suddenly you get very complex behaviour as the flock wends and wafts its way gracefully through the sky. None of this advanced behaviour is specified by the rules; it emerges from the dynamics of the system. Simple rules, as with the birds in the simulation, lead to complex behaviour. Complex rules lead to stupid behaviour.

-Andrew Hunt
The Pragmatic Programmers
(Quoted in "Getting Real: The smarter, faster, easier way to build a successful web application" by 37signals)