Whether ecosystems are structured from the top-down (i.e., predator driven) or bottom-up (i.e., food limited) has been debated by ecologists for nearly a century. Many marine and freshwater aquatic systems appear to be under top-down control, but less evidence exists that predators have had a similar effect in terrestrial systems, especially those systems involving large ungulates. Earlier research, however, omitted any serious discussion of Native Americans. Contrary to prevailing beliefs, Native Americans were not conservationists, and they had dramatic impacts on wildlife populations. Native Americans were the ultimate keystone predator and the ultimate keystone species through activities such as aboriginal burning. Moreover, the idea that North America was a 'wilderness' untouched by the hand of man prior to 1492 A.D. is incorrect, as recent population estimates indicate that native people may have numbered as many as 100 million, or more, before they were decimated by introduced diseases and other colonial processes. Until the importance of aboriginal land management is recognized and modern management practices change accordingly, our ecosystems will continue to lose the biological diversity and ecological integrity they once had, even in national parks and other protected areas. © The Wildlife Society. Abstract reproduced by permission.