If evolution is important, the reverse must also be interesting. Substantially the same techniques that are embodied in the de Bruijn diagrams can be used to determine the number of ancestors, and indeed, their actual composition. The computations are more arduous, resulting in just a few of the LCAU programs having an ancestor submenu; the prospect has not even been considered in two dimensions in CAMEX , although the theory is just as applicable.
Two aspects of the calculation of ancestors are often given special attention. One is to determine which configurations have no ancestors at all, the so-called Garden of Eden configurations. The other is to find automata for which evolution is reversible, in the sense that every configuration should have just one ancestor.