Then it is Darwin's theory of adaptation through natural selection of genetic variation; and this is an elegant example of it, and in this case variation is increased during stress by inducing mutation that allows for a greater rate of adaptation.
So if this adaptation is such a great mechanism to solve biological problems presented by the environment, what is going to prevent the DNA from diverging in separate populations until it accumulates to as much as say, between a mouse and a rat?
You have no evidence of this “solving mechanism” (there’s that language of design again) ever having led to speciation, allmendream.
What you do have is an apparent degree of commonality that is also explained just as well by design. You say common descent, I say common architecture. Either way, what has been documented is degree of genetic similarity.