Tierra's missing neutrality: case solved

Abstract

The concept of neutral evolutionary networks being asignificant factor in evolutionary dynamics was firstproposed by Huynen {\em et al.} about 7 years ago. Inone sense, the principle is easy to state -- becausemost mutations to an organism are deleterious, onewould expect that neutral mutations that don't affectthe phenotype will have disproportionately greaterrepresentation amongst successor organisms than onewould expect if each mutation was equally likely. So itwas with great surprise that I noted neutral mutationsbeing very rare in a visualisation of phylogenetictrees generated in {\em Tierra}, since I already knewthat there was a significant amount of neutrality inthe Tierra genotype-phenotype map. It turns out thatcompetition for resources between host and parasiteinhibits neutral evolution.