Prion evolution

One of the big unanswered questions in biology is what is life? Some philosophers of science have pointed out that a science (biology) where the topic of study (life) cannot be defined is unacceptable. Drawing the boundary between life and non-life is hard because of a number of discoveries that appear to exist in the gray area - from viruses, to viroids, to satellites, to prions.

Prions are just proteins and do not show metabolism or contain any nucleic acid or genetic code but they have recently been shown to undergo Darwinian selection in the same way as living organisms. Check out the Science paper from last month, Darwinian Evolution of Prions in Cell Culture, or the BBC report on the research, 'Lifeless' prion proteins are 'capable of evolution'.

"Now we know that the abnormal prions replicate, and create variants, perhaps at a low level initially.

"But once they are transferred to a new host, natural selection will eventually choose the more virulent and aggressive variants."