Difficult question, but there's an analogous question for 'carbon-based' life - are there non-carbon based life? The answer is likely "no", simply because the n

Difficult question, but there's an analogous question for 'carbon-based' life - are there non-carbon based life? The answer is likely "no", simply because the number of molecules based on carbon is many orders of magnitude larger than for the next largest (sulfur). Similarly for DNA: there are other polymers that have some of the same properties, but not to the same extent. Specifically, the ability to store information is so great in DNA. Most polymers are either regular like (-CH2-)n or random (eg lignin) while DNA (and RNA) are 'structured random', for lack of a better term. Add to this the ability to 'unzip' double-stranded DNA into two copyable halves, its great stability, and ability to be coiled up. Like water - which is another example of something with an abundance of useful features - it's very hard to see any rival molecule that could do as many things. Of course, you could just argue that we have not discovered or invented such a molecule yet. People have tried to make alternate compounds, and there are - as one of the other repliers pointed out - many variations in biology such as alternate nucleobases, or things like double-stranded RNA viruses, etc. More generally, you could of course imagine distributing the properties of DNA across multiple molecules or molecular systems. That suffers from Occam's razor a little, but cannot be ruled out, I suppose.