  The role of historical contingency in the origin of life is one of the great
unknowns in modern science. Only one example of life exists--one that proceeded
from a single self-replicating organism (or a set of replicating hyper-cycles)
to the vast complexity we see today in Earth's biosphere. We know that emergent
life has the potential to evolve great increases in complexity, but it is
unknown if evolvability is automatic given any self-replicating organism. At
the same time, it is difficult to test such questions in biochemical systems.
Laboratory studies with RNA replicators have had some success with exploring
the capacities of simple self-replicators, but these experiments are still
limited in both capabilities and scope. Here, we use the digital evolution
system Avida to explore the interaction between emergent replicators (rare
randomly-assembled self-replicators) and evolvability. We find that we can
classify fixed-length emergent replicators in Avida into two classes based on
functional analysis. One class is more evolvable in the sense of optimizing
their replication abilities. However, the other class is more evolvable in the
sense of acquiring evolutionary innovations. We tie this trade-off in
evolvability to the structure of the respective classes' replication machinery,
and speculate on the relevance of these results to biochemical replicators.
