In 1995, a small group of wolves was released into Yellowstone National Park in the United States, seventy years after the last wolves there had been hunted to extinction. The decision was controversial, and few could have predicted just how dramatically it would transform the landscape. The story of Yellowstone’s wolves has since become one of the most famous examples of how a single species can reshape an entire ecosystem.

Before the wolves returned, the park’s deer population had grown enormous, with no natural predator to keep it in check. The deer grazed heavily on young trees and plants, stripping the land bare in many areas, particularly along rivers. When the wolves arrived, they did not merely reduce the number of deer; they changed the deer’s behaviour, keeping them moving and away from the most vulnerable valleys and gorges. Freed from constant grazing, trees and vegetation began to recover.

The effects rippled outwards in remarkable ways. As forests returned along the riverbanks, birds came back, and beavers, which feed on trees, increased in number. The dams built by the beavers created habitats for fish, insects and other creatures. The regrowth of vegetation even stabilised the riverbanks, so that the rivers themselves changed course less and ran clearer. A single predator, it turned out, had triggered a chain of changes that reached all the way to the shape of the landscape.

The Yellowstone story has become a powerful symbol for the growing movement known as “rewilding”, which aims to restore natural processes by returning missing species to the wild. It is not without its critics or its complications: reintroducing large predators can create real conflicts with farmers, and the science is more complex than simple stories sometimes suggest. Nevertheless, the return of the wolf offers a hopeful lesson. Nature, given the chance, has an extraordinary ability to heal itself – and sometimes the most effective thing we can do is simply to step back and allow it to.