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Three models for the loss and/or gain of the viral envelope during evolutionary history, as well as putative host jump events. The phylogenetic tree is the same as that used in Fig. 1. (A) Early, nonenveloped viruses with subsequent gain (multiple times independently) of the viral envelope. (B) Early, enveloped viruses with its subsequent loss in multiple host lineages. (C) Early, coexisting nonenveloped and enveloped viruses.
