Viral Evolution, Morphology, and Classification

Evolution of Viruses

Although biologists have a significant amount of knowledge about how present-day viruses mutate and adapt, much less is known about how viruses originated in the first place. When exploring the evolutionary history of most organisms, scientists can look at fossil records and similar historic evidence. However, viruses do not fossilize, as far as we know, so researchers must extrapolate from investigations of how today’s viruses evolve and by using biochemical and genetic information to create speculative virus histories.

Most scholars agree that viruses don’t have a single common ancestor, nor is there a single reasonable hypothesis about virus origins. There are current evolutionary scenarios that may explain the origin of viruses. One such hypothesis, the “devolution” or the regressive hypothesis, suggests that viruses evolved from free-living cells, or from intracellular prokaryotic parasites. However, many components of how this process might have occurred remain a mystery. A second hypothesis, the escapist or the progressive hypothesis, suggests that viruses originated from RNA and DNA molecules that escaped from a host cell. A third hypothesis, the self-replicating hypothesis, suggests that viruses may have originated from self-replicating entities similar to transposons or other mobile genetic elements. In all cases, viruses are probably continuing to evolve along with the cells on which they rely on as hosts.

As technology advances, scientists may develop and refine additional hypotheses to explain the origins of viruses. The emerging field called virus molecular systematics attempts to do just that through comparisons of sequenced genetic material. These researchers hope one day to better understand the origin of viruses—a discovery that could lead to advances in the treatments for the ailments they produce.