Like I replied elsewhere, I think because nature selects for survival, there is something to be learned from the fact that human societies always tend towards hierarchy. I am not saying we should there have as much hierarchy as possible, but I am certainly opposed to any form of anarchism (which I don't believe would last long anyway). Give anarchy a month at most, and you'll have leaders with followers popping up everywhere, which will eventually combine into a smaller number of large hierarchies.