This is from Robin Lane Fox’s “The Unauthorized Version: Truth and Fiction in the Bible. He’s an Oxford scholar, pretty reliable, and his books are very readable. Here’s what he has to say about how Original Sin was constructed from the Creation story.
“These texts were creating new scripture by constructive abuse of the old, a process which reaches a climax in the letters ascribed to Paul…At Romans 5:12-18 Paul himself tells his Roman Christians how through one man, Adam, sin ‘entered into the world’ and by the sin of one man death reigned too. These famous verses have inspired whole theories of sin and original sin which have changed many Christians’ perspective on human nature. It seems clear that the Fall of Adam and Eve was not just the moral tale of a single couple’s fate: the story was meant to be the origin of a change for all subsequent humans. It is not, however, stated that what originated was sin or sinfulness, words which occur nowhere in the Hebrew text. It was St. Augustine who ended by arguing that original sin has been transmitted to each of us through Adam, a view which he backed up by Paul’s language in Romans 5. However, he followed a mistranslation of it, based only on a Latin version of the text. Paul’s Greek had merely said that ‘death passed upon all men, because all sinned’; Augustine followed an author who mistook it to say ‘death passed upon all men because of Adam, [in whom] all sinned…’ Original sin was read unnecessarily into Genesis and was then forced on to Paul by a wrong translation of his writings.”
....[Adam and Eve] “are expelled from Eden not in order to die, but so that they will not go on to further crimes and taste the tree of life. Through Adam and Eve’s misconduct, we are not condemned to death. We are condemned to hard gardening and painful childbirth; we are also denied the chance of stealing eternal life.”