I haven't been able to pin down what it is now, that determines civ levels.
The first 2 weeks our wildlife stayed at lev X, even though we already had a village up, a lot of hearthfires together, and some personal claims with large timber houses nearby.
Now, it has dropped to VII. Our hearthfires aren't cluttered together anymore as they were before, so I guess we can rule those out.
What is it? Paving? Pallisades? Cutting of trees? Or buildings / claims, but with delayed effect?
Anyone got more insights than I do?