George Johnson in The New York Times:
The powerful algorithm that has populated the earth with 10 million species, each occupying a different ecological niche, is an example of what computer scientists call “random generate and test.” Start with the DNA alphabet, then blindly shuffle the letters to produce a kaleidoscope of living forms. The fittest, selected by the demands of the environment, will multiply and fill their habitats. The Darwinian principle is also at work inside the body, though in very different ways. Through random variation and selection, the immune system spins out the endless diversity of antibodies that it uses to stop microscopic invaders. But cancer also thrives through this evolutionary imperative as, mutation by mutation, a normal human cell transforms into a deadly tumor, which becomes fitter and fitter at the expense of its host. Among the advantages it evolves is the ability to outwit our immunological defenses.
One of the most encouraging developments in medical research has been the effort to help the immune system fight back, beating cancer at its own evolutionary game. That was a dominant theme last month at the annual meeting of the American Association for Cancer Research in Philadelphia as scientists discussed recent successes in immunotherapy while considering how far the field still has to go. Why have these treatments been working so well with some cancers but not others? And why, even in the best cases, do not all patients respond? The realization that Darwinian forces, for good and bad, are at work inside us can be traced to the early 1950s, when Frank Macfarlane Burnet, an Australian virologist, was pondering how we manage to fight off a potentially infinite variety of invading microbes, tailoring an antibody against each one. One possibility was that when an interloper is identified, by its molecular bumps and grooves, the immune system systematically engineers an appropriate weapon. Nature doesn’t work in such a methodical manner, and Burnet suggested a messier, more intuitive explanation: the clonal selection theory of immunity.