At the beginning of the Christian religion, Augustine warned against the dangers of literalism. The Jewish scholars who preceded him always viewed the Genesis story as a metaphor for truths that could not be accessed in any other way. It was only with the rise of modern science that the Genesis myth came to be misunderstood as an explanatory theory.
Yet Darwinism was still a major threat to religion, for it confronted Victorians with the prospect of their final mortality. Darwin forced them to ask why their lives should not end like those of other animals, in nothingness.
If this was so, how could human existence have meaning? How could human values be maintained if human personality was destroyed at death? No one was more haunted by these questions than Henry Sidgwick.
Along with many eminent Victorians, Sidgwick could not accept revealed religion. Unlike most of them, he acted on his doubts and in 1869 resigned from his Fellowship at Trinity College, Cambridge, which required Fellows to subscribe to the Thirty-nine Articles of Anglican doctrine.
Much admired at Trinity, he was reappointed as a lecturer in Moral Science. Later Sidgwick became a professor and resumed his Fellowship. He never returned to the Christian faith he had lost. But neither did he give up hoping that theism - the belief in a Supreme Being that created the universe - might be true:
"It is now a long time since I could even imagine myself believing in Christianity in any orthodox fashion ... But as regards Theism the case is different ... I do not know whether I believe or merely hope that there is a moral order in this universe that we know, a supreme principle of Wisdom and Benevolence, guiding all things to good ends, and to the happiness of the Good ... Duty to me is as real a thing as the physical world, though it is not apprehended in the same way; but all my apparent knowledge of duty falls into chaos if my belief in the moral government of the world is conceived to be withdrawn."
Here Sidgwick gives the reason for his continuing need for belief in God. Unless theism is true there can be no "moral government of the world." In that case, living by any code of morality is senseless.
In arguing for the necessity of theism Sidgwick was not accepting the authority of religion. A thoroughly modern thinker, he accepted science as the standard by which all knowledge must be judged. If death was the end, the world was chaotic; but Sidgwick could not take life hereafter on trust. He had to have proof, and only science could supply that.
Nonetheless, Sidgwick distinguished between science as a fixed body of knowledge and science as a method of inquiry. As pictured by materialism the universe had no human meaning; but the solution was not to reject science. It was to apply the scientific method, which could show materialism to be false.
Like so many others, then and later, Sidgwick looked to science for salvation from science. If science had brought about the disenchantment of the world, only science could re-enchant it.
The result of scientific inquiry seemed to be that humankind was alone. Evolution would bring about the extinction of the species and eventually, as the sun cooled and the planet ceased to be habitable, life itself would die out. It was a desolate prospect, but one that could be accepted if science could also show that human personality would survive the universal extinction.
Paradoxically, Darwin's theory of evolution rekindled the hope of immortality. Darwin recognized the link, when he wrote in his Autobiography:
"With respect to immortality, nothing shows me so clearly how strong and almost instinctive a belief it is, as the consideration of the view now held by most physicists, namely, that the sun with all the planets will in time grow too cold for life, unless indeed some new great body dashes into the sun, and thus gives it fresh life. Believing as I do that man in the distant future will be a far more perfect creature than he now is, it is an intolerable thought that he and all other sentient beings are doomed to complete annihilation after such long-continued slow progress. To those who fully admit the immortality of the human soul, the destruction of our world will not appear so dreadful."
Sidgwick's search for evidence of survival was intertwined with his work in ethics. Unless human personality survived bodily death, he believed, morality is pointless. Theism posits a universe that is friendly to human values: goodness may go unrewarded here on Earth, but the imbalance will be righted in the hereafter. Without this assurance, Sidgwick believed, there was no reason why humans should not yield to self-interest or their passing desires.
Sidgwick feared scientific materialism because it meant humans were trapped in a "non-moral universe." He could not share the confidence of the secular thinkers of his day such as Auguste Comte, John Stuart Mill and George Eliot - who believed belief in progress could be a substitute for religion.
With his more penetrating intelligence, Sidgwick understood that this faith is an illusion. For Sidgwick morality was categorical: it told people to do the right thing. Almost by definition, moral values were more important than anything else. But why not pursue other things - beauty or pleasure, say? Why should anyone do what morality tells them is their duty? Only theism, Sidgwick believed, could give them good reason.
Victorian secular thinkers imagined that when God had faded away, morality would fill the space that was left. But when theism has gone the very idea of a categorical morality becomes meaningless.
Like Nietzsche - with whom he had very little else in common - Sidgwick understood that theism and morality cannot be separated. If belief in God is given up, the idea of morality as a system of duties soon follows.
Sidgwick was more sceptical, as well as more realistic, in doubting that the sense of duty could persist once religion had faded away. For a time people would retain their moral sense. As disbelief replaced doubt regarding the claims of religion, they might even find a sort of solace in doing their duty.
Sidgwick's argument that an afterlife could fill the hole he had found in ethics was hardly watertight. If the two principles of self-interest and universal benevolence were really contradictory, the existence of an afterlife could not alter that fact. The most an afterlife could do would be to ensure that the consequences of following the principles were the same.
But what Sidgwick wanted from theism was a world in which duty and self-interest pointed in the same direction. In such a world, he thought, the two principles would not really be at odds.
Of course a future life might be just a fact. Among Victorian seekers after immortality there were atheists and agnostics who believed that, if a future life existed, it was as part of the natural order of things. There were many who believed a future life was implied by the fact of evolution. "Spiritualism," wrote one leading advocate, the Egyptologist and poet Gerald Massey, "will accept Darwinism and complete and clinch it on the other side."
For these non-theists, Spiritualism was not a philosophy of immaterialism in which the physical world is an illusion, such as the nineteenth-century German philosopher Arthur Schopenhauer (influenced by Hindu and Buddhist thinking) had formulated. Spiritualism was another version of naturalism, an account of the material universe enlarged to encompass an invisible world.
Even if an afterlife were a natural fact, it would not mean that human personality would endure for ever. If Darwinism is true, it is hard to see how such a thing could be possible. If there is no insuperable barrier between human minds and the minds of other animals, there seems no reason why the after-world should be populated only by humans.
But if other animals also pass over into the after-world at death, do they survive as disembodied minds or do they acquire new bodies? Either way, was the after-world empty until life evolved and death appeared?
None of these questions can be answered, and in truth Darwinism cannot be reconciled with any idea of a post-mortem world. In Darwin's scheme of things species are not fixed or everlasting; their boundaries are blurred and shifting. How then could only one species go on to a world beyond the grave?
Victorian seekers after evidence of survival often imagined evolution continuing into the after-world. But they always did so in a way that distorted Darwin's vision, injecting into evolution ideas of purpose and progress for which it has no place.
John Gray is one of Britain's most prescient and controversial public intellectuals. He is Emeritus Professor of European Thought at the London School of Economics, and the author of many books, including Straw Dogs: Thoughts on Humans and Other Animals (Granta Books, 2003), False Dawn: The Delusions of Global Capitalism (Granta Books, second edition, 2009), Black Mass: Apocalyptic Religion and the Death of Utopia (Penguin, 2008) and Gray's Anatomy: Selected Writings (Penguin, 2009). This article is an edited extract from his most recent book, The Immortalization Commission: Science and the Strange Quest to Cheat Death (Penguin, 2011).