Full Idea
Candidates for the most important idea in human history are: mimetic thinking (imitation), the soul, the experiment, the One True God, the heliocentric universe, and evolution.
Gist of Idea
The big idea: imitation, the soul, experiments, God, heliocentric universe, evolution?
Source
Peter Watson (Ideas [2005], Ch.03)
Book Reference
Watson,Peter: 'Ideas: from fire to Freud' [Phoenix 2006], p.72
A Reaction
From this list I would choose the heliocentric universe, because it so dramatically downgraded the importance of our species (effectively we went from everything to nothing). We still haven't recovered from the shock.