Socrates, Swammerdam, and Paley had drawn from the adaptations of nature proofs of the omnipotence and beneficence of the Creator. Darwin, while admitting that every organism is exquisitely adapted to its own mode of life, believed that the adaptations have been perfected by slow degrees, and that they cannot be proved to have been consciously devised. This interpretation deprives the theologian of valued arguments, but at the same time rids him of difficulties. Even before Darwin's day some few natural theologians had the courage to bring forward instances of the harshness of nature. Kirby and Spence[48] thought that no injustice was done to certain predatory insects by comparing them to devils. Others blessed the mercy of heaven, which, after creating noxious animals, created others to keep them in check. Darwin, when reflecting upon the odious instincts which urge the young cuckoo to eject its foster-brothers, some species of ants to enslave others, and a multitude of ichneumons to lay their eggs in the bodies of live caterpillars, found it a relief to be able to shift the responsibility to an unconscious natural process.[49] In his autobiography Darwin remarks that he had thought it almost useless to endeavour to prove by indirect evidence that species had been modified until he was able to show how the adaptations could be explained. Some of them alarmed him by their difficulty; to suppose that the eye, with all its inimitable adjustments, had been formed by an unconscious natural process seemed to him absurd until he had traced a good many intermediate steps between the mere colour-spot and the eye of the eagle. He writes to Asa Gray (September 5, 1857) that the facts which had done most to keep him scientifically orthodox were facts of adaptation, the pollen-masses of Asclepias, the mistletoe with its pollen carried by insects and its seeds by birds, the woodpecker exquisitely fitted by feet, tail, beak, and tongue to climb trees and capture insects.