What if we have wild mutations AND exceptionally good exception handling?
First mechanism - to go into production you have to pass unit tests (race to the egg). It's only 1 cell, so either it works or not, and if you were the fastest you probably didn't have most of the really bad mutations.
Then after you are in production you run million copies of the code, and to be safe against mutations there's sth like erlang exception handling - if sth's wrong kill the process, start a new one.
The problem is - sometimes the process gets so wrong it doesn't respond to kill signal.
How did they arrive at this conclusion?
The mutations that makes you immobile - the same.
The mutation that mess up with your instincts, and reactions to chemical enzymes - same (you won't go the right way).
And so on.
It's a little like unit testing - it checks all the basic routines.