Much has been speculated about the identities of the skeletons in the cave that we were introduced to in Season One. We have had information from Jack to indicate that, given the deterioration of the clothing, that the bodies must have been in situ for 50 years and have taken this at face value but Jackis a spinal surgeon, not a forensic pathologist or anthropologist and he may be wrong (or at least off by a decade or two).
If we accept this as a valid claim then I propose that Adam and Eve are, in fact, Daniel and Charlotte. Both died during time travel episodes (on Island), we have not seen or been told what happened to their bodies and the rate od deterioration would apply. It could be that they were reunited in death in a way that we are not yet privy to but I think that it could just as much be Daniel and Charlotte as any of the other couples that have been suggested, and with a sounder rationale than Bernard and Rose for example.