Stigmergy: the most important concept you’ve never heard of

[…] The concept of “stigmergy” is at precisely this stage today: sufficiently well-defined to provide us with a fundamental new insight about nature, life and society, but not yet widely known.

The principle underlying stigmergy is so simple that once once you have understood this, it becomes impossible to unsee: An action produces a trace or mark in an external medium. Perceiving the mark stimulates a next action.