How about an experimentaltrack of thought today; that is, I don’t claim it to be true, but thinking this line of thought might inspire some other insights. The thoughts are about “the Fall”, the biblical story when the snake convinced Eve to eat from the forbidden fruit, and she gave Adam, and he ate, too. (Gen 3).
There is reason to assume that the second “special tree” in Eden had a medical / bodily effect: it was named the “tree of life”, and only after man was prohibited to eat from it, he started to die bodily. So it could be that its fruit contained some (yet unknown and in nature no longer existing) vitamine, that the human body needs to survive eternally on earth.
Here come the experimental thoughts: this quality of the “tree of life” does not mean, however, that the “tre of the knowledge of good and evil” was likewise special, in a material sense. Perhaps it was just a normal tree that was just named specially. (Perhaps the Grapefruit tree, as this fruit was named Citrus paradisi for some time … just kidding). Now, if the effect of eating from the tree would have been only spiritual (in the sense of being implemented as brain activity), we’d have to explain how.
The most obvious effect (that made God “curious” as to what happend) was that Adam and Even were both ashamed of their nakedness after eating from the fruit. They had hidden from each other and from God. Now, what is hiding away if not the effect of losing trust. It seems easy to imagine how Adam and Eve discussed, after eating from the fruit, if it was correct to do so, then debated, then got into a verbal fight with each other. No more trust, as they had done wrong to each other. Eve had given Adam to eat from the fruit thing, and Adam, while standing all the time there, had not protected Eve from eating this thing first.
Nearly everybody can remember a bad conscience experience in his or her childhood: it’s very intense, because conscience is not yet hardened by the knowledge that doing evil and doing wrong is commonplace, and by being personally accustomed in doing the same. In childhood, when doing consciously and deliberately wrong for the first few times, the effect is intense: the child feeld hot and cold, hides away, cannot look into the eyes of its mom and dad, and it’s very obvious that the good quality of relationship has gone away.
This experience (and even more intense, as experienced by understanding adults) might have happened to Adam and Eve. No need for any special substance in the fruit to generate all the problems with sin that started to enter the world at this point. Because sin is, basically, a spiritual entity: a kind of self-reproducing program in the brain of humans, that passes on to other humans by “copying” (learning from each other) and has destructive effects in everybody’s life. Just like a computer virus for the brain.