Prey by Michael Crichton, Day 6 08:12am

Nor were individual birds genetically programmed for flocking behaviour. Flocking was nto hard-wired. There was nothing in the bird brain that said, "When thus-and-such happens, start flocking." On the contrary, flocking simply emerged within the group as a result of much simpler, low-level rules. Rules like, "Stay close to the birds nearest you, but don't bump into them." From those rules, the entire group flocked in smooth coordination.
Because flocking arose from low-level rules, it was called emergent behaviour. [p125]