Figure 2.

Evolution in the presence of stereotyped noise. M = 100, R = 2, μ = 0.005/element/generation. (A) Fitness improves steadily over two orders of magnitude. Labels c, d, and e indicate the generations used to generate the corresponding lower panels. (B) Noise vulnerability V_noise, defined as the population mean of the fraction of network elements whose states depend on noise information, for the 25 output elements (solid) and the set of all elements causally connected to the output (dashed). V_noise invariably increases to near unity as evolution progresses, indicating that the network structure that evolves has higher functional connectivity than the randomly constructed starting network. (C) Random output of the starting network (solid), the target function (dotted), and the fixed randomly chosen binary noise pattern (Lower). (D) The network evolved after 2,500 generations generates a good approximation of the target function. (E) The same network as in D but operated in the absence of noise fails completely, indicating that the evolved network has been “imprinted” by the arbitrary noise sequence present during its evolution and requires it to function.