Europeans ate their way through the island nation of Mauritius, most famously eliminating the dodo bird by 1700. Less well known was their effect on the Mauritian island now known as Ile aux Aigrettes, where they exterminated giant skinks and tortoises and logged the native ebony trees for firewood.

In 1965 the largely denuded 25 hectares of the island were declared a nature reserve. But even in the absence of logging, the slow-growing ebony forests failed to thrive. Why? Because they had lost the animals that ate their fruit and dispersed their seeds. So in 2000 scientists relocated four giant tortoises from the nearby Aldabra atoll in the Seychelles, and by 2009 a total of 19 such introduced tortoises roamed the island, eating the large fruits and leaving behind more than 500 dense patches of seedlings. The team reported its results in April in the journal Current Biology.

For this tiny island, at least, rewilding appears to have worked. And that holds out hope for other restoration ecology projects in the midst of the sixth mass extinction in the earth’s history. In Europe conservationists have received €3.1 million to begin bringing bison, bovines and horses back to “abandoned” agricultural lands in places such as western Spain or the Carpathian Mountains. Ecologists have proposed repopulating parts of the U.S. with elephants, which would replace extinct mastodons. The Dutch, for their part, have already built what amounts to a Pleistocene park at Oostvaardersplassen, adding Konik horses and Heck cattle to replace extinct wild horses and cattle.

Of course, humans have a mixed track record when it comes to interfering in natural ecological systems—the introduction of the cane toad to Australia to manage other pests has resulted in a frog march of havoc across the continent. “There are no guarantees when trying to manipulate nature,” notes ecologist Mark A. Davis of Macalester College in Minnesota. Others argue that humans should fix what they have broken. “There is no place on this planet that humans have not interfered with, and it is time for us to become actively involved in engineering solutions,” says marine biologist Ove Hoegh-Guldberg of the University of Queensland in Australia. “There are no other options except extinction at this point.”