This is a question, variants of which, I have been asked, and have seen asked of others, many times.
"How can you explain DNA in evolutionary terms"
If you take it at face value it is fairly easy to answer, it only asks for an explanation after all - so any plausible hypothesis should do the trick.
Here is one, just off the top of my head.
Life begins as an inevitable result of the general movement toward thermodynamic equilibrium in appropriate systems, and among all the various forms of rudimentary life that are produced some have the capacity to absorb others and use the material to increase in size. These must have some sort of basic coding/instruction system to allow this building. Now either one of the life forms arising from thermodynamics also has the capacity to use this coding/instruction to split into two, or one of the coding systems goes wrong and results in a split rather than death. (if the chances of such an event were, say, 1 in 10 million billion billion, then it should have occurred about 14 times by now) So now we have life that splits, but the coding isn't perfect, so occasional mutations creep in, and so evolution begins. Over time complexity grows, both in the organism and in its coding system, eventually giving rise to basic protein type things, which in turn lead to better coding in a precursor to RNA, which paves the way for actual RNA, and so on to DNA.
So, there is an explanation in (very) basic evolutionary terms. It's light on the detail of course, and not established by research (and in any case researchers are likely to have their own, much better, ideas to examine). But that is not why those who ask the question will reject the answer.
They will reject any answer because the question is disingenuous - it is not a request for an explanation, it is a disguised statement to the effect that -
"You cannot prove this particular thing therefore..."
And the therefore... is the false "God of the Gaps" argument
In standard form it would go something like this
(1) Phenomenon X occurs
(2) There is no proof of the cause of X
(3) If there is no proof of any other cause, supernatural agent Y must be assumed to be the cause
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(4) Therefore (from 1,2, and 3) Agent Y must exist
A very common argument despite its obvious flaws
(5) The argument contains the fallacy of "circularity" in that the existence of agent Y is assumed in premise (3) and then stated as the conclusion (4).
(6) The basic form of premise (3) is flawed, e.g. before there was proof of the existence of DNA the coding process was not carried out by some other thing or agent.
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(7) Therefore (from 3,4,5,and 6) the "God of the Gaps" argument is false.
<which is the thing I said it was>
