Some biologists have made a case for DNA replication evolving twice, independently: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/pdf/273389.pdf http://ww

Some biologists have made a case for DNA replication evolving twice, independently: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/pdf/273389.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC148579/pdf/27338... Apparently you can also make a case for the evolution of DNA itself, possibly from a 2-letter alphabet: http://arxiv.org/abs/0710.0445 http://arxiv.org/abs/0710.0445