DID A HIGH MUTATION RATE EMERGE AS A SIDE EFFECT OF SELECTION FOR FAST REPLICATION?
One simple possible alternative to the adaptive value of the high mutation rate is the existence of a trade-off between replication efficiency and fidelity; i.e., increasing fidelity would come at a cost, resulting in a lower replication rate (10, 24). Biochemical assays of HIV-1 mutants resistant to nucleoside reverse transcriptase inhibitors suggest that this might be the case (1, 35). This hypothesis is in good agreement with RNA virus ecology. RNA viruses represent an extreme case of r-selection (i.e., selection for fast replication with poor resource exploitation), in which faster replicators are favored. As expected under r-selection, experimental evolution of viral populations faced with constant environments demonstrated that growth rates always increased dramatically (4, 6, 16, 19, 32, 37, 47). Therefore, shorter genomes might be favored by natural selection due to their fast replication, even with a fidelity cost. However, further experimental evidence is needed to support th
