Viruses are probably polyphyletic, with different lineages arising through escaped genetic elements, reduction of cellular parasites, or ancient pre-cellular replicators.
The diversity of viruses is consistent with more than one evolutionary origin, rather than one simple family tree from a single first virus.
Some viruses resemble escaped genetic elements, some may descend from reduced cellular organisms, and others may have assembled from ancient replicators. Similar functions can evolve independently, so shared genes must be interpreted with context.
When comparing origins, ask:
A capsid gene shared by distant viruses may indicate transfer or convergent function; it does not alone prove one direct ancestor.
‘All viruses evolved from one virus’ is stronger than the evidence supports.
A strong HL virus answer usually combines two moves: define the boundary, then explain the mechanism or consequence. Viruses have DNA or RNA plus a capsid but lack the machinery for independent metabolism. Their diversity is described by genome, capsid, and envelope. Lambda phage lets you contrast lytic takeover with lysogenic integration. Origin questions require competing hypotheses and polyphyly. Evolution questions require mutation, recombination, short cycles, large populations, and examples such as influenza or HIV.