Fig. 8

The results of a theoretical model (not, as it is sometimes described, a “simulation”) developed by Nilsson and Pelger (1994) to test the time required for a complex camera-type eye to evolve through a series of gradual steps from a simple patch of light-sensitive tissue consisting of an outer protective layer, a layer of receptor cells, and a bottom layer of pigment cells. The number of generations passing between each step is indicated, based on a change of only 0.005% in some parameter (length, width, or protein density) per generation with changes resulting in an improved calculated image formation retained each time. Although this model assumes a strictly gradualistic, linear model that is not necessarily the route that camera-type eye evolution actually took (Fig. 10; Table 1), it does show two important things: (1) that even very minor changes can improve image formation gradually and (2) that the time taken for this process to occur, less than 400,000 generations even under rather conservative assumptions, is remarkably fast in an evolutionary sense. From Land and Nilsson (2002) based on Nilsson and Pelger (1994), reproduced by permission of Oxford University Press and The Royal Society