Single-step and multi-step evolution towards an XOR phenotype. The highlighted edges of each network correspond to the environmental transitions made during evolution (evolutionary path). The value of each edge corresponds to the average time to evolve a fit phenotype, in number of epochs. <T> and P are the average total time (traversing through the highlighted path) and the success probability (ratio of successful experiments over total experiments). (A) Direct evolution in an XOR environment is very slow and has a low probability of success (B-C) evolution to environments of lower complexity and subsequent evolution to the final environment accelerate evolution and boosts the number of successful experiments, (D) The presence of HGT in a population that pre-evolved in two simple environments further increase the evolution rate, (E) step-wise acceleration can occur in more than two steps, although at a lesser degree.