you may have better luck in /r/askscience here is one I found with a very quick search this is just due to the fact that there in my understanding very limited oral or written history over 8000 years old which is a fraction of the time humans have been a species hence historians will not have much to base answers off and anthropologist may have a better time

(http://www.reddit.com/r/askscience/comments/1e863u/what_is_the_entire_population_of_human_history/)