Theories of Viral Evolution

Analysis of viral genetic material suggests viruses DO NOT come from a single common ancestor.

Three hypotheses to explain the origin of viruses:

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.•

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)

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)