The quick brown fox jumped over the lazy dog.
Or how about this?
Let's assume that any "mutation" that doesn't create a readable sentence is thrown away but any mutation that leaves the sentence to be readable will stay in the "population".
Ok:
The quick brown fox jumped over the lazy do
t.
Still readable.
The qui
et brown fox jumped over the lazy dog.
Still readable.
The quick fox jumped over the lazy dog. [deleted brown]
ditto.
The quick brown fox jumped over the lazy
brown dog.
ditto (and part is duplicated, hmmmm.)
The quick brown fox jumped over the
stupid lazy dog.
no problems here. Now can you imagine what would happen over time with the sentence as more mutations act upon it over time. Eventually it isn't going to be recognizable from what it was before.