Many viruses (including SARS, influenza, HBV, HCV, and HIV) encode their genome in RNA rather than DNA. Unlike DNA viruses, RNA viruses lack the ability to detect and repair mistakes during replication [1] and, as a result, their mutation rate can be as high as 1 mutation per each 1,000-100,000 bases copied per replication cycle [2] . Many of the mutations are well tolerated and passed down to descendants, producing a family of co-existing related variants of the original viral genome referred to as quasispecies, a concept that originally described a mutation-selection balance [3] [4] [5] [6] [7] .