" RNA viruses are limited to small genomes because their mutation rates are so high, and their mutation rates are so high because they’re limited to small genomes. In fact, there’s a fancy name for that bind: Eigen’s paradox. Manfred Eigen is a German chemist, a Nobel winner, who has studied the chemical reactions that yield self-organization of longer molecules, a process that might lead to life. His paradox describes a size limit for such self-replicating molecules, beyond which their mutation rate gives them too many errors and they cease to replicate. They die out. RNA "

― David Quammen , Spillover: Animal Infections and the Next Human Pandemic