Confounded cytosine! Tinkering and the evolution of DNA

Abstract
Early in the history of DNA, thymine replaced uracil, thus solving a short-term problem for storing genetic information — mutation of cytosine to uracil through deamination. Any engineer would have replaced cytosine, but evolution is a tinkerer not an engineer. By keeping cytosine and replacing uracil the problem was never eliminated, returning once again with the advent of DNA methylation.