Host-Virus Arms Races and the Red Queen

 

"It takes all the running you can do, to keep in the same place."

-- The Red Queen, in Lewis Carroll's Through the Looking Glass


Viruses cause disease, and more susceptible individuals die with bias. In this way, all organisms have evolved highly refined mechanisms of viral immunity. But because viruses evolve rapidly, continued selection to adapt to a "moving target" results in the simultaneous rapid evolution of host genes that defend against viruses. This creates an ever-escalating arms race between host and virus. The evolutionary "Red Queen" hypothesis addresses such immunity genes, which must constantly keep step with viruses on their accelerated evolutionary course.



New adversaries grinningly replace the losers

“ We can think of the Red Queen's Hypothesis in terms of an unorthodox game theory. To a good approximation, each species is part of a zero-sum game against other species. Which adversary is most important for a species may vary from time to time and for some or even most species no one adversary may ever be paramount. Furthermore, no species can ever win, and new adversaries grinningly replace the losers. 


From this overlook we see dynamic equilibria on an immense scale, determining much of the course of evolution by their self-perpetuating fluctuations. This is a novel way of looking at the world, one with which I am not yet comfortable. But I have not yet found evidence against it, and it does make visible new paths and it may even approach reality. “


-- By Leigh Van Valen, University of Chicago, 1973, Evolutionary Theory