You will have notices swarms of insects, for example, swarming around a light. These insects apparently have all spontaneously decided to 'buzz' the light. Is there a lead insect that gives orders, or that they follow. Biologists don't think so.
Similarly you can observe flocks of birds. For example is a bunch of pigeons are suddenly disturbed while feeding on the ground they will fly together in a swirling motion towards some place of safety, such as a roof. This is flocking. Again, there might appear to be a leader selecting the safety perch, but studies have shown that this is not true. Certain kinds of fish exhibit similar behaviour. They travel in schools, as a group, with no apparent leader.
Here we see again, global, collective, organized behaviour, apparently being generated from local individual actions of individual members of the swarm, flock or school.
(from the boids example below)
Each boid has direct access to the whole scene's geometric description, but reacts only to flock mates within a certain small radius of itself. The basic flocking model consists of three simple steering behaviors:
(from the author's web page)
(1) If you don't know where bread crumbs** are, try to find some.
(2) If you see another ant, ask if they know where bread crumbs are. If they know, head toward them. If not, run away from that ant (because after all, food probably isn't near them if they don't know where food is.)
(3) If you find bread crumbs, take it back to the hole, and return to the place where you found food (because where there is food, there is probably more food.) If you don't find any crumbs where you thought they were supposed to be, start searching again (and tell other ants there is no food there).
The emergent behaviour generated by these rules is quite amazing. The antz behave like ants!
local version of the antz applet. source etc (zip file)
It might seem that these aLife things are just for fun. However, there are appliclations.