Here was my idea. I call it “The Wedge.” See, there’s this wedge of, well, effect, emanating from the cluster of black hoes near the center of the galaxy, and sweeping around like a lighthouse beam, with one rotation every several thousand years (details to be worked out). While The Wedge is shining on your plant, things work one way. When it passes, things go back to normal. Our solar system has been within the Wedge Zone for thousand of years (except may be it flicked off now and then, say, during Egyptian times, or whatever). Never mind the details.
In Poul Anderson’s Brain Wave (a novel*) which is at this exact moment available by Kindle for a mere $1.99 (at least in the US), instead of a galaxy level wedge, there is a magnetic force that switches off. The magnetic force has been keeping intelligence out of the evolutionary process on Earth. Mostly. Then it goes off.
My story might be better. In my story, the solar system has plenty of intelligent life forms that know all about the Wedge. Then,they show up on Earth in advance of the Waning of the Wedge, which is going to result in a world in which current Earthling Science will suddenly have access to technology that will allow the ravaging and conquering of other worlds. So they send this guy with this big metal killing machine, in order to have a talk with the Earth’s world leaders but then he get shot and “killed” and … well, you get the point.
So, anyway, I’m glad that I can pick up Brain Wave for next to nothing!