For most of us, viruses are the stuff of nightmares — mysterious micro-agents spreading pandemics like Ebola, polio, and HIV. But there’s much we are still learning about the virosphere, from the origins of viruses themselves to their effects on evolution and the natural world.
In their book Viruses as Complex Adaptive Systems, SFI External Professors Ricard Solé (Universitat Pompeu Fabra) and Santiago F. Elena (Spain National Research Council) employ biology, physics, and mathematics to understand the impact of viral robustness and pervasiveness. “Viruses are everywhere,” says Solé. “Emergent viruses are an inevitable consequence of the novel opportunities provided by overpopulation, from humans to cattle, and the disruption of diverse ecosystems.”
The secret to the success of viral evolution lies in their population size and generation time, which allow viruses to skirt the effects of mutation that can cripple the advancement of other species. “Population size for viruses is massively larger than for their hosts,” says Elena. “And while generation time for humans is 25 years, for lytic viruses (those killing the infected cell), it is hours or, at best, days.”
But what exactly are viruses? And are they even alive? Defining viruses and understanding their role in various ecosystems is complicated by the range of viral complexity and the unknowns surrounding their genesis. “The origin of viruses is still a quite open and debated topic,” says Elena. “Likewise, some people still consider them as nonliving entities.”
In 1992, a group of scientists stumbled upon the Mimivirus, a giant virus whose genome is both large and elaborate. This discovery directly called into question previous wisdom that viruses are small and simple, closer to androids than living beings. “The more we find new viruses, the more blurred are the boundaries,” says Solé. “The problem is that biology offers multiple exceptions to most definitions of living that you can provide.”
However, computer viruses, which most would agree are not living, provide a neat analogy for biological viruses and offer insights into their complexity. “The parallels between virus evolution and computer virus evolution are rather remarkable,” says Solé. Although computer viruses are man-made, they also operate through infection (in this case, of computer memory, not of cellular hosts), diversify their traits, and evolve to combat antiviral software.
“The more we learn about viruses, the more complex mechanisms of interaction we find,” says Solé. Viruses as Complex Adaptive Systems uses many different vantage points to create a more fully realized picture of viral complexity, even while most of us continue to primarily interact with viruses through a bout of the winter flu.