Theory and Empiricism in Virulence Evolution

Dobzhansky famously wrote, “Nothing in biology makes sense except in the light of evolution.” Given the importance of viral evolution to disease emergence, pathogenesis, drug resistance, and vaccine efficacy, it has been well studied by theoreticians and experimentalists. Indeed, as the highly theoretical concepts of quasispecies and error catastrophe gained mainstream attention over the last thirty years, notions of viral populations and viral evolution became almost inseparable for many virologists. In contrast, a large body of theoretical work on the evolution of virulence has yet to gain traction in the virology community. Our purpose here is to offer a brief introduction to virulence theory, explain some of its strengths and weaknesses, and suggest how theory might be united with empiric data. While we focus our discussion on viruses, many of the concepts presented are similarly applicable to other prokaryotic and eukaryotic pathogens.