I noticed this too, that the evolution stayed at 0.0 for nearly the whole game of at least 200 hr. The only time I saw it bounce up above zero were:
Exploring far from base once and a forest fire started by fire spitters must have caused enough pollution to get to 1-2%, before dropping back down in less than a minute.
The big Rampant v2 update recently caused evolution to spike to 85% while recalculating changes (causing a lot of panic and havoc that luckily ended as quickly as it started). I kind of ignored the 0% evolution issue until this happened, then I started to dig into it again.
I did start the game with a large starting area, was relatively green, and killed spawners in my pollution cloud for first half of game. For latter half though I get an small, easily deflected, pollution induced attack about once a minute once I stopped caring about pollution.
The /rampantEvolution command was informative:
0%: Current Evolution
18.54%: Tile Absorbed Pollution Contribution
-631.26%: Tree Absorbed Pollution Contribution
82.46%: Tree Damaged by Pollution Contribution
15.42%: Spawner Absorbed Pollution Contribution
2%: Killed Spawners Contribution
-0.01%: Killed Units Contribution
(Rest were zero)
Maybe I will play with setting for tree absorbed pollution, after installing some nontrivial defenses.