We are currently in the midst of earth's "sixth great extinction." For the past 10,000 years, existing species have been dying out faster than new species have been evolving, say scientists. Big Think expert and famed Harvard biologist E.O. Wilson has estimated the annual species extinction rate to be around 30,000, and the International Union for Conservation of Nature calculated that the rate of extinction is 100-1,000 times greater than it was before man evolved. And with the threat of further climate change and man's exponential population growth, things are only getting worse. 

Conservationist and Cornell visiting fellow Josh Donlan tells Big Think that to mitigate this extinction, we should not just be trying to slow the rate of biodiversity loss—we should actively be working to reverse it. We must be "pro-active," he says, insisting on "countering the default scenario of more homogeneous landscapes." And the answer, he says, is to reintroduce big game animals like elephants and lions into middle America. "Big animals tend to be very important for generating biodiversity in the long haul," says Donlan.

Most conservationists set their benchmark for conservation of North America at 1492, the year Columbus landed in the New World, but Donlan argues we should push the clock back even farther, when these large animals roamed the great plains. Historical narratives paint the Europeans' arrival as having devastated a pristine Americans, but man had been responsible for environment change for millenia. Humans arrived in North America around 13,000 years ago, and their arrival heralded the extinction of dozens of species of fauna, especially large animals. Donlan says North America lost around 65 species over 100 lbs. around this time. 

Repopulating North America's extinct big animals might be possible (even without cloning wooly mammoths from DNA in their fossils, as some have proposed) because many of the species that died out in North America have very similar relatives elsewhere in the world, says Donlan: the African lion is almost genetically identical to one that lived in North America; the Asian or African elephant could serve as a proxy for the mammoths that once roamed the Great Plains; and we even once had cheetahs roaming our continent. Re-wilding North America would not only help restore biodiversity here, it would repopulate big species like the African elephant, which are in danger of extinction.

Donlan imagines creating a giant ecological park in economically depressed parts of the MidWest. "As in Africa and regions surrounding some North American national parks, nearby towns would benefit economically from land management and tourism-related jobs," he says.