 The comparability of these very different media can be taken further, because of the capabilities discussed already for maintaining a “frozen fossil record” by reviving ancestral populations and studying their evolutionary trajectories. This allows researchers to “back up” a population’s evolutionary trajectory and “rerun” it an arbitrary number of times from an earlier timepoint, by defrosting and reviving (repeatedly) a frozen ancestral population sample (e.g., Travisano et al. 1995). This backing up and re-running of population trajectories is very similar to the recursivity of algorithms in computer simulations. It also resonates with thought experiments such as Gould’s (1989) famous idea about “replaying the tape of life”. While Gould originally presented the thought experiment as a metaphor, and had in mind rewinding and replaying all of life on earth, long-term microbial evolution experiments show how at least a subset of “life”s tape’ can actually be replayed (see Beatty 2006 for discussion of the extent to which this sort of experimental work fits Gould’s ideas about his thought experiment).