Richard Hollerith: Herds of bison on the American plains numbered around 50 million in the mid 19th century numbered 60 to 100 million http://en.wikipedia.org/wiki/American_Bison . With a conservative 800 lbs/bison of meat and 8 year replacement time, that suggests a mostly bison diet could feed 15M-25M hunters on just the US great plains if herds were used efficiently and more plausibly 5M-10M with more likely levels of efficiency. A single river with a salmon run can support a primitive fishing town with a few tens of thousands of people. Throw in Africa and Asia and I would expect a few tens of millions of human hunter-gatherers. This is still consistent with a 3 to 5 fold increase in population due to the shift to agriculture, which could easily be enough to cause the replacement of hunter-gatherers (though I have alternative speculations as to what may have happened in this case) and another 3 to 5 fold increase in population subsequent to the development of agriculture but prior to industrialization due to several thousand years of improved crops, irrigation, fertilization, pest control, and organizational institutions (broadly, capital improvements). I don’t know of ANY model for hunter gatherer populations which seriously suggests that they would have grown approximately smoothly and exponentially rather than expanding to carrying capacity with some overshoot like other animals. Intuitive models for agriculture suggest a roughly linear or geometric trend ultimately leading to diminising returns as good farm land is depleted from the dissemination of agriculture followed by an initially slower exponential trend from the multiplicative impact of innovations such as better tilling methods or hybrid grains.
Richard Hollerith: Herds of bison on the American plains numbered around 50 million in the mid 19th century numbered 60 to 100 million http://en.wikipedia.org/wiki/American_Bison . With a conservative 800 lbs/bison of meat and 8 year replacement time, that suggests a mostly bison diet could feed 15M-25M hunters on just the US great plains if herds were used efficiently and more plausibly 5M-10M with more likely levels of efficiency. A single river with a salmon run can support a primitive fishing town with a few tens of thousands of people. Throw in Africa and Asia and I would expect a few tens of millions of human hunter-gatherers. This is still consistent with a 3 to 5 fold increase in population due to the shift to agriculture, which could easily be enough to cause the replacement of hunter-gatherers (though I have alternative speculations as to what may have happened in this case) and another 3 to 5 fold increase in population subsequent to the development of agriculture but prior to industrialization due to several thousand years of improved crops, irrigation, fertilization, pest control, and organizational institutions (broadly, capital improvements). I don’t know of ANY model for hunter gatherer populations which seriously suggests that they would have grown approximately smoothly and exponentially rather than expanding to carrying capacity with some overshoot like other animals. Intuitive models for agriculture suggest a roughly linear or geometric trend ultimately leading to diminising returns as good farm land is depleted from the dissemination of agriculture followed by an initially slower exponential trend from the multiplicative impact of innovations such as better tilling methods or hybrid grains.