>He also analyzed the DNA sequence known as PAM, which allows microbes to distinguish between their own genomes and the genomes of viruses. Without PAMs, a bacterium could easily kill itself. But the new study – of which Mojica is a co-author – indicates that some of the oldest CAS enzymes are capable of cutting DNA accurately without the need for PAM.

The old-one probably was fast in recombination/evolution in the early days....until PAM came along and was utilized as a fail-safe mechanism against eating the good part of itself and thus survived and multiplied.

Good that we are evolved enough to work around billion years old fail-safe mechanisms. Now I just ponder about DNA that can be transcribed more efficiently when you get rid of all the unnecessary redundancy. Maybe replace it with a QR-code only to buy your daily protein infusion.