Viral evolution theories suggest that viruses did not come from a single common ancestor. There are three main hypotheses for the origin of viruses: that they devolved from cellular organisms like bacteria and lost components over time; that genetic material escaped from cells wrapped in a protein coat; or that self-replicating particles co-evolved alongside cells and adapted to new cell types.

1. Theories of Viral Evolution

2. Analysis of viral genetic material suggests
viruses DO NOT come from a single common
ancestor.
Three hypotheses to explain the origin of
viruses:

3. 1. Devolution (Regression) Hypothesis
•Viral ancestors were cellular organisms similar
to bacteria.
•Evolved into obligate parasites
•Parasites lost cellular components as it was
more efficient to reproduce without.
•

4. 2. Escapist (Progressive) Hypothesis
•Genetic material from a free living (non-parasitic)
cell “escaped” wrapped in protein coat
•Explains viral-host specificity (viruses are able to
attack and take over host because they came from
them)

5. 3. Self-Replication (Co-evolution)
Hypothesis
•Particles with the ability to self-replicate
evolved alongside the cells
•As new cell types evolved, new viruses that
could target that cell evolved (co-evolution)