On a recent episode of TWiV, we posed the question, 'Can computer viruses evolve'? and asked listeners to weigh in. The author of the blog nostacktrace spent some time thinking about this issue and concludes that the evolution of real computer programs doesn't really work. Software instructions are very brittle. They cary out a specific set of instructions, and those instructions are so densely coded that almost all mutations or recombinations would yield completely non-functional programs. But he agrees that computational evolution might not be impossible.