I've had to teach the Adam and Eve story recently. This has meant trying to look at the story from a palatable angle, whilst still making it comprehensible to the younglings.
The result of my musings was thus:
Of course, that means leaving God out of it, which does undermine the idea somewhat (since the loss of innocence first stems from disobedience to Him) but the basic idea seems sound. From a folk point of view you are seeking to resolve two unavoidable facts: you know what good behaviour should be, but you do not always adhere to it. How to explain this apparent contradiction? This way: the tree of knowledge produces fruit (i.e. your own moral awareness) but there is a selfishness, a desire, that counters one's own best instincts. Now, the knowledge of good and evil must be closely related, and it is not immediately clear that one must be prior to the other: the knowledge of good and evil must be present for temptation to be meaningful, but if temptation is tempting one away from that which is good, it implies that temptation must also be a post-good artefact, like the knowledge of the difference.
Interestingly, the addition of a God to the mix is not required here. But if you assume that the myth was devised in a mythologically/theologically predisposed society it does not seem unreasonable to demand a place for a deity i n this scheme. Of course, this is not a historical argument but an ideological one. The structure and content of the story is the key issue here and so it does not matter particularly if this was a myth created by a monotheistic society of an adaptation/translation of earlier myths. Once a supernatural being of any kind is proposed, by it's nature it supercedes the natural order expressed in the physicalities of trees, serpents, apples and talking ribs. The interesting features of the Biblical creator-God are that it is (a) uniquely powerful and (b) benevolent. So if you take the benevolence of the instigator of conscience and temptation as given, it is beyond self-evident that the prior state of conscience and temptation is benevolent. Hence the doctrine of original sin.
But it is equally clear that the main thrust of the argument is not disobedience to God. This is an effect of the introduction of the benevolent creator-God hypothesis. The real key of the story is to highlight a co-relation between conscience and temptation. The existence of good and evil is in fact a given, and the real issue is to explain how, if we know that there are good things and bad we still choose the bad.
Now of course to modern eyes what is absolutely fascinating about this story is its absoluteness. There is no room for context - and I don't just mean that there is no sociological account of the construction of morality. Rather what I mean is that there is a cast-iron assumption that we do, or at least should, know right from wrong; that one cannot be prevented from carrying out an immoral act, and that evil comes from temptation, since temptation would indicate any form of desire, regardless of how apparently harmless or even noble, judging from Genesis 3:4-6:
4. And the serpent said unto the woman, Ye shall not surely die:
5. For God doeth know that in the day ye eat thereof, then your eyes shall be opened and ye shall be as gods, knowing good and evil.
6. And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.
It's practically Buddhist. Still, the moral of the story that seems to be both the most unavoidable and generally useful is this: conscience and temptation are closely related, even entangled, and alongside conscience, evil is an inevitable feature of human nature.
Or, as Solzhenitsyn once put it...
If only there were evil people somewhere insidiously committing evil deeds and it were necessary only to separate them from the rest of us and destroy them. But the line dividing good and evil cuts through the heart of every human being. And who is willing to destroy a piece of his own heart?