Genetics and the Spiral Staircase
Next time you look into a mirror, gaze into your eyes, those remarkable, colorful organs of sight whose worth and beauty have been sung in story and song. Each is an intricate camera with a lens that focuses colored pictures on a sensitive film. The film is the retina, located at the back of the eye, and after the pictures are registered there, they are sent along the optic nerve to the brain. But just how they are transmitted, and how they are actually seen by us, remains unclear.
Equally baffling is how these sophisticated organs arose and developed at all. Geneticists, specialists in that branch of biology that deals with inheritance, assume that the eyes emerged gradually in the same slow mutational process that changed single-celled organisms to simple, multicellular forms, and then directed these, in turn, so that some evolved into plants, others into insects, and still others into animals. Some organs, like the appendix in humans, became small and useless, while others, like the