I will discuss how transfer of genetic information between individuals influences the phase diagram and mean fitness of both the Eigen and the parallel, or Crow- Kimura, models of evolution. In the absence of genetic transfer, these physical models of evolution consider the replication and point mutation of the genomes of independent individuals in a large population. A phase transition occurs, such that below a critical mutation rate an identifiable quasispecies forms. I will generalize these models of quasispecies evolution to include horizontal gene transfer. I will show how transfer of genetic information changes the phase diagram and mean fitness and introduces metastability in quasispecies theory, via an analytic field theoretic mapping.