The pristine natural world has been gone for a long time; get used to it.
Nearly all of the earthworms in New England and the upper Midwest were inadvertently imported from Europe. The American earthworms were wiped out by the last Ice Age. That's why when European colonists first got here, many forest floors were covered in deep drifts of wet leaves. The wild horses of the American West may be no less invasive than the Asian carp advancing on the Great Lakes. Most species of the tumbleweed, icon of the Old West, are actually from Russia or Asia.
The notion that America was "wild" when Europeans found it is more than a little racist; it assumes Indians didn't act like humans everywhere else by changing their environment. Native Americans weren't Ur-hippies taking only photos -- or I guess drawings -- and leaving only footprints. They cultivated plants, cleared forests with extensive burning to boost the population of desired animals, and otherwise altered the landscape in ways that may have seemed natural to newcomers but were nonetheless profound. As biologist Charles Kay observes, "Native Americans were the ultimate keystone species, and their removal has completely altered ecosystems ... throughout North America."
Kay goes on to note that when we set aside a "wilderness" and then let "nature take its course," we aren't preserving "some remnant of the past." We are instead creating "conditions that have not existed for the last 10,000 years."
And even then, these supposedly wild places aren't truly wild. That's because to the extent they are preserved in their seemingly natural state, it is by humanity's will. Also, the remaining wild animals in those places are often the ones we decided should live or didn't accidentally kill. And the plants and animals that ate -- or were eaten by -- those creatures have never been the same. Without humans, dogs, cows, pigs and chickens wouldn't have evolved the way they have.
The wild environment isn't just about trees and bears and other forms of charismatic mega flora and fauna. I heard Bill Gates on NPR the other day talking about the great strides his foundation has made against malaria and how we may be on the brink of actually eradicating polio forever. Diseases play a huge part of any natural ecosystem, and we've been trying to drive them to extinction for centuries.
In other words, we pick and choose what should be "wild" and what shouldn't all of the time.