  Because organisms synthesize component molecules at rates that reflect those
molecules' adaptive utility, we expect a population of biota to leave a
distinctive chemical signature on their environment that is anomalous given the
local (abiotic) chemistry. We observe the same effect in the distribution of
computer instructions used by an evolving population of digital organisms, and
characterize the robustness of the evolved signature with respect to a number
of different changes in the system's physics. The observed instruction
abundance anomaly has features that are consistent over a large number of
evolutionary trials and alterations in system parameters, which makes it a
candidate for a non-Earth-centric life-diagnostic
