De-Extinction is the idea of resurrecting animals we killed off through cloning and selective breeding. Scientists are currently working on creating a mammoth clone or genetically engineered arctic elephant to be transported to the arctic in order to complete the long left ecological role they played in the arctic grasslands. Horses, bison, tigers, wolves and musk ox are being transported to Russia and in North America, there is talk of cloning the Passenger Pigeon, a pigeon that was hunted to extinction by man for cheap slave meat in the 18th century. Researchers are breeding primitive breeds of cattle and releasing them into the wild to replace their ancestors and extinct subspecies, the aurochs.