Easy, we do not even know when or where civilization started, and we can't ever know that the world now represents the highest level of civilization, we do not know the cataclysmic past of this planet, we have regularly suppressed archeological evidence by burning and dumping artifacts that do not fit the established paradigm. In summary, history is a mystery and that is by design. As example, and just one, the histories of North America refuse to teach about the mound builders of this continents earliest yet identified inhabitants,these mounts in the early eighteen hundreds numbered in the thousands, artifacts recovered included, copper and iron tools, script similar to, Sumerian, none of it part of popular histories. The total destruction of flora and fauna of North America at around, 12,500 BC by cometary entry to the biosphere, avoided like the plaque. So in summary of the sciences history is the most unreliable and misused to base any conclusions on especially one so insane as the OP presents. No figures whatever exist to support his claims and to make such claims he must be totally and willfully ignoring the fact of the dismal state of recorded reliable human history. We have no idea of ancient population numbers which could with ease have been much higher than they are today, as was the case with the big reptiles.