I think the driving force for cultural evolution is this desire for groups to be splitting off and separating and forming subgroups insofar as the environment will allow it. We see great cultural diversity and large numbers of cultures per unit area in regions of the world in which the environment is really rich.
Humans like to think of themselves as unusual. We've got big brains that make it possible for us to think, and we think that we have free will and that our behavior can't be described by some mechanistic set of theorems or ideas. But even in terms of much of our behavior, we really aren't very different from other animals.