  The most prominent property of life on Earth is its ability to evolve. It is
often taken for granted that self-replication--the characteristic that makes
life possible--implies evolvability, but many examples such as the lack of
evolvability in computer viruses seem to challenge this view. Is evolvability
itself a property that needs to evolve, or is it automatically present within
any chemistry that supports sequences that can evolve in principle? Here, we
study evolvability in the digital life system Avida, where self-replicating
sequences written by hand are used to seed evolutionary experiments. We use 170
self-replicators that we found in a search through 3 billion randomly generated
sequences (at three different sequence lengths) to study the evolvability of
generic rather than hand-designed self-replicators. We find that most can
evolve but some are evolutionarily sterile. From this limited data set we are
led to conclude that evolvability is a likely--but not a guaranteed-- property
of random replicators in a digital chemistry.
