The first aquatic creatures crawled onto dry land in the Silurian era, more than three hundred million years ago. They may have been unprepossessing brutes, but had they been clobbered, the evolution of land-based fauna would have been jeopardised. Likewise, the post-human potential is so immense that not even the most misanthropic amongst us would countenance its being foreclosed by human actions.

Martin Rees, Our Final Hour: A Scientist’s Warning: How Terror, Error and Environmental Disaster Threaten Humankind’s Future in this Century—On Earth and Beyond, New York, 2003, p. 183