Andrew Grant in Discover:
Most current research into the causes of cancer focuses on genes and environmental triggers. Evolutionary biologist Paul Ewald of the University of Louisville in Kentucky argues that scientists have overlooked the most important cause: parasites, especially viruses. Blending medicine and Darwinian biology, Ewald considers cancer and other diseases from the pathogen’s point of view, showing how natural selection determines why the smallpox virus, for instance, is a ruthless killer while viruses for the common cold are relatively benign. He says that once we identify the viruses that trigger cancer, we can work to prevent their transmission and force them to evolve from fatal scourges into mere nuisances, eventually turning cancer into a manageable disease.
DISCOVER: What is new about the way you are thinking about disease?
Paul Ewald: I apply Darwinian principles to medicine with the goal of solving problems. Medicine is not very good at addressing evolution, and to me that’s a great problem in regard to infectious disease. Humans barely evolve quickly enough to adjust to rapidly evolving infectious agents.
D: Why do you believe that viruses lie behind many types of cancer?
PE: To progress toward cancer, you need a few specific genes to be mutated, within a limited number of cell divisions, to cause the cells to divide uncontrollably. But if you mutated almost any of the other 30,000 genes, the cells would die or be crippled. So how do all those specific mutations occur so rapidly without destroying the cells? It turns out that each virus that’s been studied and associated with cancer—such as hepatitis B with liver cancer or human papilloma virus with cervical cancer—evolves characteristics that allow it to target those genes immediately upon infection. They’re pushing cells to the brink of cancer because the cells will grow faster with the virus embedded inside and won’t be able to stop dividing. These viruses don’t really benefit if you get cancer, but they do benefit when the viral genome can replicate and persist despite a sophisticated immune system.