I think there might have been a tipping-point crossed when the brain achieved a certain capacity. Of course, cultural aspects were critical to catalyse this phenomenon, which is evident when you examine remote tribes such as those in the southern Nicobar islands, who are anatomically modern humans, but behave more or less like advanced orangutans.
A sort-of runaway event that lead us to be what we are today. Nonetheless, natural selection is very much in play here. By ‘natural’ I include those actions that human individuals influenced, as well. We are a part of the natural world.
By that definition what isn't natural? Man made, managed, or altered by definition is not natural. Modern humans have very little to do with nature, and many of us have a false impression of what nature is from watching Hollywood entertainment. It's a stretch to say humans living in modern civilization are a part of the natural world.