I think we were both hunters and gatherers for the great bulk of human and pre-human history and we certainly eradicated all the large mammals (and huge birds) from most of the world - Africa was the exception because the gradual evolution of human hunting gave that fauna time to evolve antipredator behavior towards human hunting. Subsequent to those extinctions, I don't think that agriculture per se was responsible for environmental devastation - that has been due to the immense increase in human numbers that agriculture, domestic livestock, and much more recently, medicine, has made possible. The earth would be in fine shape if there were perhaps one billion people; with eight billion, we and our children are witnessing the eradication of a vast number of species and the destruction of most ecosystems. All environmental problems are the result of too many people.
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