" Forced to carry tiny genomes, viruses could not make room for genes that did anything beyond make new viruses and help those viruses escape destruction. They could carry genes to let them eat, for example. They could not turn raw ingredients into new genes and proteins on their own. They could not grow. They could not expel waste. They could not defend against hot and cold. They could not reproduce by splitting in two. All those nots added up to one great, devastating Not. Viruses were not alive. "

― Carl Zimmer , A Planet of Viruses