That is the same question, as I assume you know, which Philip Johnson claims he put to Dawkins. Their exchange (Johnson's version of it) is described here. Dawkins' purported response seems correct:
... the reason we know for certain we are all related, including bacteria, is the universality of the genetic code and other biochemical fundamentals.Johnson then waves it all away (like a good creationists) and, in effect, says: "You have no proof! Nyaaaa nyaaa, nyaaaaa!" [That's not a fake quote, it's my own interpretation of Johnson's silly position.]
Well, I'm not surprised you don't answer my query.
Are you sure all DNA codes are the same. ..and did that code 'create' itself?