Might be something with the latest version that your evolution clamping isn't doing or just a vanilla bug, was working fine on 17.21, decided to get everything to latest versions, and ran into a little problem... what wasn't spawning big biters is now spewing them out, even though we're clamped at 8.4% from tech. the nests claim we're at 53%!

https://i.imgur.com/ufa8g6X.jpg

Probably related to:
https://mods.factorio.com/mod/research_causes_evolution/discussion/5c96296d43820f000b8a378d

thanks for the report. i am not sure where the problem is at the moment; i haven't tried my mod yet with the latest factorio version although i don't expect that to be the problem, but i will test it. it could also be a mod interaction issue - specifically i am wondering if any of the used mods adds additional forces for biters. (my mod only changes the factor for the force called "enemy")
Can you provide me your full list of mods? then i can take a look. I had a quick look at rampant but that seemed fine, so i have to go further.
i think the linked issue that "Research Causes Evolution" had doesn't affect mine, since my mod did not consider the ai_controlled value.

Well, it is ai_controlled, but it's because your mod didn't consider it. Rampant (and Biter Factions) both use their own ai_controlled factions that aren't enemy_faction. I did a test and used the code from RCE to call your script on both, and it worked flawlessly. https://i.imgur.com/L4qvf2B.jpg

Here's my edited file if you want it. https://drive.google.com/open?id=1iDRzFHyD2Rka8jU3v5cKd7NvdfydN1PJ

thanks! i now uploaded a new version that changes it like you proposed

Thanks man. Also makes it compatible with Rampant, which I know is really popular.

well when i was reading through Rampant it looked like they always used the "enemy" force, so i am curious if Rampant actually affects Biters when used together with Biter Factions. Maybe in your game you have some mix now where Rampant detects nest building, but not biter death for pheromones (since Biter Factions assigns them to factions after creation). could be tricky to check that one though