> Something clearly operated to keep human population in check before its explosion over the last couple of centuries. But it was generally not starvation. The real problem is that population growth begets population density, and population density, in the absence of sanitation, antiobiotics, and other checks on infection, begets disease and death

That's an interesting opinion, but how does that model explains why eastern Asian countries (where rice was available) where able to achieve and sustain far higher population density than areas fed by wheat?

Also, pre-modern cities like Rome or Baghdad where much more densely populated than the average and have seen such population level for centuries, which means than population density in the rural world was far lower than some hypothetical limit level.