In 1986 a computer scientist named Craig Reynolds wondered about how birds flock, and if they do so through some form of central control, or whether they use principles of self-organization.
He wrote a computer program in which a number of "boids", a word he created, all follow the exact same rules. As it turned out, these virtual birds behaved...the "flocked"...in a way that was visually very similar to what we see from real birds.
Here's the original video he made, 30 years ago: