We have no idea what happens in our own code, code that we copy from place to place ourselves, written in languages we designed and running on machines we designed, and there's nothing like mutation and self-replication with this stuff, for the most part.
Documented: Computer viruses mutating in the wild by two different viruses accidentally copying themselves into overlapping regions of memory.
Interesting. When has that happened? It seems awfully unlikely to create "viable offspring" that way, but I suppose most biological mutations are neutral or negative as well...
Documented: Computer viruses mutating in the wild by two different viruses accidentally copying themselves into overlapping regions of memory.