It might seem hardly worth questioning the idea that the world is made for seeing, or that eyes are consequent upon the undeniable fact that there is so much to be seen. Yet think for a moment and the inevitability of vision is much more uncertain. The world is full of signals that may be used to describe it: there are smells, chemical signals both subtle and ubiquitous, and touch is as sensitive to shape as site- more so, because it cannot be misled by trompe l’oeil
or by camouflage. Imagine a world in which the eye had never developed- not the eye of the insect, nor of fish, nor of mammal, nor yet Mankind. It easy to conceive of the other senses having taking over the comprehension of their surroundings. It would be a world of palpation, of feelers, a world in which caresses would have rendered glances superfluous. The twitching and waving of antennae would accompany every action. It is not difficult to imagine that a different evolutionary course would have selected those organs most delicately attuned to the passing molecule: even now we know of moths so sensitive to the pheromones of the opposite sex that the most evanescent whiff of a mate can stimulate a love flight across kilometers. In a sightless world, sensitivity to such stimuli would be selected and refined: it would be a world of nuance so delicate that our gross maulings would be inconceivable.
In conscious animals this most sensory of environments would entail everywhere the language of touch and smell: beauty would be aural or tactile or olfactory. Poetry would not celebrate the unfathomable mysteries of eyes and their unplumbable depths, or compare hair with flax, for visual similes would be redundant. Rather, the texture of skin might be the supreme erotic stimulus, or natural selection might have favored an ever more elaborate array of perfumes and chemical attractants, which in turn would evolve a language of which we can only dream. There might be symphonies of perfume, Mozarts of musk. Novelists might construct nasal narratives, versifiers sonnets of scent. Sculpture would entail subtleties of shape that only fingers trained through hundreds of millions of years of tactile evolution could discriminate. There would be no word for “blindness”.
So I don’t believe that light inevitably engendered sophisticated sight, simply that that particular path was taken by life on this planet, elaborating and improving upon the simple photosensitivity of single-celled organisms. The eyes of the trilobite are tangible proof of a selection of one special branch of evolution from an array of possible alternatives- an innovation that made the world visible. Once passed, this threshold could not be forgotten, even if some animals- trilobites included- once more lost sight of the world in favor of fumbling in the dark.