Regarded objectively, as an espisode in the development of life on earth, a nuclear holocaust that brought about the extinction of manking and other species by mutilating the ecosphere would constitute an evolutionary setback of possibly limited extent—the first to result from a deliberate action taken by the creature extinguished but perhaps no greater than any of several evolutionary setbacks, such as the extinction of the dinosaurs, of which the geological record offers evidence. […] However, regarded subjectively, from within human life, where we are all actually situated, and as something that would happen to us, human extinction assumes awesome, inapprehensible proportions. It is of the essence of the human condition that we are bornm live for a while, and then die. Through mishaps of all kindsm we may also suffer untimely death, and in extinction by nuclear arms the number of untimely deaths would reach the limit for any one catastrophe: everyone in the world would die. But although the untimely death of everyone in the world would in itself constitute an unimaginably huge loss, it would bring with it a separate, distinct loss that would be in a sense even huger—the cancellation of all future generations of human beings. According to the Bible, when Adam and Eve ate the fruit of the tree of knowledge God punished them by withdrawing from them the privilege of immortality and dooming them and their kind to die. Now our species has eaten more deeply of the fruit of the tree of knowledge, and has brought itself face to face with a second death—the death of mankind. In doing so, we have caused a basic change in the circumstances in which life was given to us, which is to say that we have altered the human condition. The distinctiveness of this second death from the deaths of all the people on earth can be illustrated by picturing two different global catastrophes. In the first, le ut suppose that most of th people on earth were killed in a nuclear holocaust but that a few million survived and the earth happened to remain habitable by human beings. In this catastrophe, billions of people would perish, but the species would survive, and perhaps one day would even repopulate the earth in its former numbers. But now let us suppose that a substance was released into the environment which had the effect of sterilizing all the people in the world but otherwise leaving them unharmed. Then, as the existing population died off, the world would empty of eople, until no one was left. Not one life would have been shortened by a single day, but the species would die. In extinction by nuclear arms, the death of the species and the death of all the people in the wold would happen together, but it is important to make a clear distinction between the two losses; otherwise, the mind, overwhelmed by the thought of the deaths of the billions of living people,  might stagger back without realizing that behind this already ungraspable loss there lies the separate loss of the future generations.

Jonathan Schell, The Fate of the Earth, New York 1982, pp. 114-115