From Lankaster to Lorenz, scientists have gotten it wrong. Parasites are complex, highly adapted creatures that are at the heart of the story of life. If there hadn't been such high walls dividing scientists who study life - the zoologists, the immunologists, the mathematical biologists, the ecologists - parasites might have been recognized sooner as not disgusting, or at least not merely disgusting. If parasites were so feeble, so lazy, how was it that they could manage to live inside every free-living species and infect billions of people? How could they change with time so that medicines that could once treat them became useless? How could parasites defy vaccines, which could corral brutal killers like smallpox and polio?
Carl Zimmer, Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures
evolution, parasites, vaccines