P.S. Regarding Crocodile's statements about Paleolithic food-production -- Croc definitely should've used some qualifying phrase like "per capita", but otherwise the observation has empirical evidence from archeology to support it.

For example, some Paleolithic hunters definitely used the hunting method of "stampeding the entire herd of bison over the cliff to their deaths; then butchering five or six bison for their meat and hides while leaving the rest of the dead animals to rot in the sun." * On a per capita basis (that is, considered as a ratio of the number of animals killed against the number of humans who were sustained by the meat and hides harvested) this stampede-hunting was almost unbelievably wasteful and inefficient, but since human populations were so small, the inefficiency wasn't very destructive to the environment. Also, some primitive agricultural peoples used the wasteful practice of deliberately burning down large areas of forest or grassland in order to kill two birds with one stone: it quickly got rid of the native plants so that the open fields could be planted with crops, and also enriched the soil with ashes.

Nowadays, we are in many ways vastly more efficient at food production, but our population numbers are also vastly larger, and thus our "total environmental footprint" as a species is bigger/worse than in Paleolithic times.

* At least some American Indians apparently continued to use this method until Europeans reintroduced ** the horse to North America, as well as firearms. Horses and guns from Europe made it possible for Native Americans to hunt more selectively and efficiently than they ever had in pre-Columbian times, killing only as many animals as they needed. Meanwhile, some of the Europeans went around shooting thousands of bison just "for sport" from moving trains, thus helping to create the modern perceptions about wasteful white people vs. indigenous-brown-people in harmony with Mother Earth.

** Some scientists believe that horses went extinct in the Americas (where they had originally evolved, and had lived for millions of years) because they were overhunted by the prehistoric humans who had recently invaded arrived in the Americas from Siberia. So the Europeans HAD TO "reintroduce" the horse to America because the ancestors of nature-loving Amerindians had totally wiped out the animals! Mind you, this theory is difficult to prove with certainty, and an alternative hypothesis is that long-term climate changes and the resulting changes to vegetation were the main factor that killed off the equines in their native continent. It may also be that there's truth to both hypotheses -- that climate change had caused the population of horses to shrink dramatically, and overhunting by prehistoric humans was the "final nail in the coffin". There's little doubt, however, that Paleolithic hunters who arrived via the Bering Strait did cause "stress" to indigenous American mammal populations, thousands of years before the white Europeans arrived across the Atlantic.