1 Set of hunches. 2  If a theory is a set of hunches, it means we arenât yet sure we have the answer. 3  Theories always involve an element of speculation or conjecture. 4  A theory is not just one inspired thought or an isolated idea.  A theory offers some sort of explanation.
Uracil is paired with thymine in RNA and it is paired with Adenine in DNA. In DNA transcription (from DNA to RNA), uracil pairs with adenine. in regular DNA replication adenine pairs with thymine.
Now - by complete chance - deamination of cytosine results in uracil. Had DNA not switched from uracil to thymine, the deamination damage to cytosine would be essentially impossible to detect. But since thymine is used by DNA, uracil can be correctly recognised as damaged and repaired back to cytosine with thymine as template.