Another dynamic facet of living cells that display multiplicity of attractors is transcriptional networks that control shifting expression patterns, which mediate cell type transitions. Employing a Boolean analysis of such gene regulatory networks, a study based on information for nearly 1,600 human transcription factors (67) validated the proposal (68) that such networks converge upon attractors in gene expression space, and that some of the attractors showed expression patterns reminiscent of experimentally observed cell types . In laboratory experiments, when external chemical inputs were applied, the trajectories moved out of the realm of one computationally predicted attractor into the basin of another attractor. The same attractor shift elicited by environmental changes was observed in in-silico analyses of multilevel evolution .