Bill Bryson,

“I mention all this to make the point that if you were designing an organism to look after life in our lonely cosmos, to monitor where it is going and keep a record of where it has been, you wouldn't choose human beings for the job.But here's an extremely salient point: we have been chosen, by fate or Providence or whatever you wish to call it. It's an unnerving thought that we may be living the universe's supreme achievement and its worst nightmare simultaneously.Because we are so remarkably careless about looking after things, both when alive and when not, we have no idea-- really none at all-- about how many things have died off permanently, or may soon, or may never, and what role we have played in any part of the process. In 1979, in the book The Sinking Ark, the author Norman Myers suggested that human activities were causing about two extinctions a week on the planet. By the early 1990s he had raised the figure to about some six hundred per week. (That's extinctions of all types-- plants, insects, and so on as well as animals.) Others have put the figure ever higher-- to well over a thousand a week. A United Nations report of 1995, on the other hand, put the total number of known extinctions in the last four hundred years at slightly under 500 for animals and slightly over 650 for plants-- while allowing that this was "almost certainly an underestimate," particularly with regard to tropical species. A few interpreters think most extinction figures are grossly inflated.The fact is, we don't know. Don't have any idea. We don't know when we started doing many of the things we've done. We don't know what we are doing right now or how our present actions will affect the future. What we do know is that there is only one planet to do it on, and only one species of being capable of making a considered difference. Edward O. Wilson expressed it with unimprovable brevity in The Diversity of Life: "One planet, one experiment."If this book has a lesson, it is that we are awfully lucky to be here-- and by "we" i mean every living thing. To attain any kind of life in this universe of ours appears to be quite an achievement. As humans we are doubly lucky, of course: We enjoy not only the privilege of existence but also the singular ability to appreciate it and even, in a multitude of ways, to make it better. It is a talent we have only barely begun to grasp.We have arrived at this position of eminence in a stunningly short time. Behaviorally modern human beings-- that is, people who can speak and make art and organize complex activities-- have existed for only about 0.0001 percent of Earth's history. But surviving for even that little while has required a nearly endless string of good fortune.We really are at the beginning of it all. The trick, of course, is to make sure we never find the end. And that, almost certainly, will require a good deal more than lucky breaks.”