After decades of researching the impact that humans are having on animal and plant species around the world, Chris Thomas has a simple message: Cheer up. Yes, we’ve wiped out woolly mammoths and ground sloths, and are finishing off black rhinos and Siberian tigers, but the doom is not all gloom. Myriad species, thanks in large part to humans who inadvertently transport them around the world, have blossomed in new regions, mated with like species and formed new hybrids that have themselves gone forth and prospered. We’re talking mammals, birds, trees, insects, microbes—all your flora and fauna. “Virtually all countries and islands in the world have experienced substantial increases in the numbers of species that can be found in and on them,” writes Thomas in his new book, Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction.

Thomas is a professor of conservation biology at the University of York in England. He is not easily pigeonholed. He has been a go-to scientist for the media and lawmakers on how climate change is scorching the life out of animals and plants. At the same time he can turn around and write, “Wild geese, swans, storks, herons and cranes are returning as well, and the great whales, the largest animals ever to have lived on Earth, are once more plying their way across our seaways in numbers after centuries of unsustainable butchery.” Glass half empty, meet Chris Thomas.