Symmetry breaking and adaptation: evidence from a 'toy model' of a virus

We argue that an induced breaking of the genetic synonym symmetry due to th e action of genetic operators such as mutation can enhance the adaptability of a species to changes in the environment. In the case of a virus', the c laim is that the codon bias in the neutralization epitope improves the viru s' ability to generate mutants that evade the induced immune response. We s upport our claim with a simple 'toy model' of a viral epitope evolving in c ompetition with the immune system. The effective selective advantage of a h igher mutability leads to a dominance of codons that favor non-synonymous m utations. As further evidence we present a simple model for a genetic regul atory network that leads to adaptive evolution in a population of giraffes by means of an induced symmetry breaking rather than through any direct sel ective advantage. (C) 1999 Elsevier Science Ireland Ltd. All rights reserve d.