The Sixth Extinction is the title of a book published in 1995 by the paleo- anthropologist, Richard Leakey and the award-winning science writer, Roger Lewin. They subtitled their book, Biodiversity and its Survival. They pointed out that over the last 530 million years there have been five mass extinctions of species, the fourth 65 million years ago, when the dinosaurs disappeared. Their book was at once a celebration of the biodiversity of animal and plant life on our planet – Darwin’s “endless forms most beautiful” – and a severe warning, backed up by analysis of the science, that we may now be on the verge of a sixth extinction, caused this time, not by an asteroid collision, but by ourselves. Human beings, they contended – “with their relentless expansion and limitless appetites” – are now able to exert as much influence on life around the world as the calamity that caused the last great extinction.