In Alaska, hunters will be allowed to use bait when they go after grizzly bears in a 3,000-square-mile area near the Canadian border, but not because of problems with humans. The practice will be allowed for the first time since Alaska gained statehood because grizzlies are being blamed for the decimation of the moose population in parts of the interior of the state.
In some areas where bears and people have been rubbing shoulders too much, authorities have been trying some novel approaches to separate the two.
In addition to trying to teach humans how not to encourage bears to dig into their garbage cans for food, police and game officials in some towns in California, Colorado, New Mexico and other states in the West have been armed with guns that shoot beanbags, horns that blast loud noises and other devices to annoy bears found roaming too close to town.
"The first time bears come into a residential area, before they've gotten addicted to human food and don't associate humans with food, it works fairly well," Klein said. "Once they've gotten addicted to human food, it won't work anymore."
In New Jersey, there is a $100 fine for feeding bears, and in Colorado you can be fined for even inadvertently feeding bears, for example, if your garbage is left out in containers that bears can open.
Of all the big predators, though, it is probably the gray wolf that has raised the most opposition, even though it would seem that it poses the least direct threat to humans. According to wolf biologists with the U.S. Fish and Wildlife Service, there are no recorded fatal attacks on humans by a healthy wolf in North America.
But wolves have a taste for livestock.
"Livestock people generally detest, loathe and fear them, and sometimes with good reason," Quammen said.
Wolf populations in Montana, Idaho and Wyoming have reached levels where Fish and Wildlife is ready to de-list them and turn management over to the states, but that plan has been held up over a dispute between Wyoming and the federal government over the state's proposed management plan.
Wyoming's plan, backed by ranchers concerned about their herds, would allow wolves to be shot on sight in most of the state.
But the return of the wolf to the Northern Rockies has provided a valuable lesson for biologists, because of the wide-ranging effects on the environment they have seen there. The effects were not limited to the wolf's prey, but extended to vegetation and even erosion patterns, and none of it was expected.
"If we didn't know about it for wolves, one of the most closely studied species, I don't even want to say what we don't know for the effects of other species," Fascione said. "You want to play it safe, because once a species is gone, it's gone."
The dispute over the wolf is emblematic of the whole problem, though, because, scientists say, people on both sides of the argument do not really see the animal clearly, either taken in by its charisma or seeing it as evil because of its skill as a predator of sheep and cattle.
"Our big problem is we don't understand adequately the complexity of nature, how animals and humans can all fit into the system," Klein said. "We have the potential, we have the knowledge -- if we use it -- to create a beautiful environment, but people have to be educated."
ABC News affiliate KATU-TV in Portland, Ore., contributed to this report.