As the most numerous and genetically diverse biological agents on Earth, viruses populate the oceans in quantities that dwarf the number of stars in the universe—yet their evolutionary origins remain elusive. A recent study published in Frontiers in Virology offers fresh perspectives on how viruses may have originated and diversified over time.
The origins of viruses remain one of biology’s most enduring puzzles, with several competing hypotheses in play. Did viruses escape from cellular organisms, evolve from more complex cells that lost functionality, or even predate the first cells themselves? To explore one of these possibilities — the escape hypothesis originally proposed by Forterre and Krupovic — scientists from the Department of Biology and the Bipartisan Commission on Biodefense conducted an in-depth analysis using both theoretical modelling and numerical simulations.
The escape hypothesis suggests that viruses may have started out as bits of genetic material that broke away from living cells. Over time, these fragments developed the ability to survive on their own and infect other cells, eventually evolving into the viruses we know today.
This new study has determined that for viruses to successfully emerge and persist via the escape hypothesis then both the viral death rate and the infected cell death rate must exceed a minimum threshold. If these death rates are too low, the system doesn’t allow enough selection to drive the evolution of the infectious traits (like spreading efficiently). Higher death rates force the virus and infected cells to replicate faster and more efficiently in order to survive – which is what allows a virus to evolve and become persistent in a population.
In addition, cell division must be imperfect – otherwise the system remains too uniform and there’s nothing to drive the emergence of virus like elements.
As the lead author of the study John O’Brien, DPhil student in Biology and researcher at the Bipartisan Commission on Biodefense, explains, certain biological pressures are essential for viral evolution:
“Our findings show that viruses can only emerge and persist if there’s enough pressure to drive evolution—without high enough death rates or uneven cell division, there’s simply no spark.”
Finally, they investigated different ways that the early virus may reproduce to see which is more effective.
Co-author of the study, Michael Bonsall, Professor of Mathematical Biology in the Department, says:
“We compared the slow and steady method—budding—with the fast, aggressive strategy of lysing — split cells open to release new virus — to explore how early viruses might have chosen their path to survival. Although both methods were proven to be effective, overall, shorter reproduction delays were better for virus survival.”
Asha George, Director of the Bipartisan Commission on Biodefense, concludes:
“Numerical modelling allows us to simulate complex biological processes—like the evolution of viruses—in ways that are impossible to observe directly. In this case we were able to get a compelling look at how simple genetic elements might have escaped cellular life and evolved into the viruses we know today.”
Understanding these origins can help scientists better predict and respond to emerging viruses by revealing how new infectious agents can arise.
To read more about this research, published in Frontiers in Virology, visit: The origins of viruses: evolutionary dynamics of the escape hypothesis.
