Probably plenty of factors, including chance, mostly chance I suspect. A combination of particular needs, like what you are describing, opportunities, like the

Probably plenty of factors, including chance, mostly chance I suspect. A combination of particular needs, like what you are describing, opportunities, like the right species of plants and animals, the rights ideas, enough success for the agricultural tribes to survive and a willingness to expand and develop the ideas. It can take quite a while before everything goes together.