  Which factors govern the evolution of mutation rates and emergence of
species? Here, we address this question using a first principles model of life
where population dynamics of asexual organisms is coupled to molecular
properties and interactions of proteins encoded in their genomes. Simulating
evolution of populations, we found that fitness increases in punctuated steps
via epistatic events, leading to formation of stable and functionally
interacting proteins. At low mutation rates, species - populations of organisms
with identical genotypes - form, while at higher mutation rates, species are
lost through delocalization in sequence space without an apparent loss of
fitness. However, when mutation rate was a selectable trait, the population
initially maintained high mutation rate until a high fitness level is reached,
after which organisms with low mutation rates are gradually selected, with the
population eventually reaching mutation rates comparable to those of modern
DNA-based organisms. These results provide microscopic insights into the
dynamic fitness landscape of asexual populations of unicellular organisms.
