When confronted with environmental change, the presence of so many diverse mutations is an advantage. When the human body creates antibodies to fight the virus, for example, there are always a few mutants that turn out to be unscathed and live to reproduce. This is the reason that HIV is notoriously difficult to treat. One drug cannot kill off all the diverse mutations. Some always survive.
Error catastrophe takes a different approach.
Loeb and Mullins speed up the viral mutation by introducing a compound known as a nucleoside analog. The mutation rates are so high that too many damaging mutations accumulate and too few viruses survive to maintain the infection. In eight out of the nine cultures treated, the HIV levels declined below measurable levels. Most of the mutations do no harm. But eventually the virus accumulates so many errors that they inactivate it.