The rogue proteins behind variant CJD, the human form of mad cow disease, have revealed their benign side. Prions, it seems, lie at theheartofa newly discovered form of near-instant evolution that provides life with a third way to adapt to potentially lethal environments. Crucially, it involves neither genetic nor epigenetic changes to DNA. The conventional view is that new traits can only evolve if DNA itself changes in some way. The classic way to do this is by mutating the genetic code itself. More recently, researchers have discovered that molecules can clamp onto DNA and prevent some parts of the sequence from being read, leading to genetic changes through a process that is known as epigenetics.
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