Herb, Alice, and Hal, the Baby

If there were alternate structures that preserved the information, evolution would continue　unimpeded. This claim can be further examined in yet another intuition pump. Imagine that on another　planet, “odd-numbered” generations used the DNA rungs A, C, G, and T, and “even-numbered” generations used a different double helix, call it XNA, with rungs made of P, Q, R, and S (some other molecules). We can suppose that the offspring’s XNA molecules were made from DNA templates from their parents by a mechanism rather like messenger RNA, but “translating” between the two different biochemical languages.

Philosopher Daniel Dennett's Book Intuition Pumps