Did it happen all at once, or in certain parts of the world first?
What role did language play in this?
What was an average number of people in a group in a hunter gatherer society? How about agrarian?
Hi there, this is a good question, but you might have better luck over in either /r/asksocialscience, /r/askanthropology, or possibly even /r/askscience, as they have a greater critical mass of people who study the development of prehistorical social structures.