  The concept of neutral evolutionary networks being a significant factor in
evolutionary dynamics was first proposed by Huynen {\em et al.} about 7 years
ago. In one sense, the principle is easy to state -- because most mutations to
an organism are deleterious, one would expect that neutral mutations that don't
affect the phenotype will have disproportionately greater representation
amongst successor organisms than one would expect if each mutation was equally
likely. So it was with great surprise that I noted neutral mutations being very
rare in a visualisation of phylogenetic trees generated in {\em Tierra}, since
I already knew that there was a significant amount of neutrality in the Tierra
genotype-phenotype map. It turns out that competition for resources between
host and parasite inhibits neutral evolution.
