Adam came up with the tiny mad idea

"Adam's "sin" could have touched none of you, had you not believed that it was the FATHER Who drove him out of Paradise. For it is in that belief that knowledge of the Father was lost, for it is only those who do not understand Him that COULD believe it."

This statement suggests that in fact someone named "Adam", in heaven, was the first to come up with the tiny mad idea. Notice that it says that ADAMS SIN could have touched NONE of you, ie no other brother besides this one individual. And that this one individual seemed to be the first who left paradise. And it was only our own belief in the same idea that made us join him. So we can seemingly attribute the invention of the tiny mad idea to Adam, just as is similarly written in the bible in relation to Adam eating of the tree of the knowledge of life and death etc. Adam was the first to enter the "original sin".

Even though the bible's account of this story may be slightly too literal and augmented, nevertheless ACIM does seem to indicate there was a "garden of eden" (heaven), there was a kind of misuse of knowledge leading to the realm of fragmentation and hierarchies of illusion (tree with branches and leaves), the symbol of eating of its fruit (temptation to believe the mad idea), temptation by the serpent/devil (ego belief etc), expulsion from heaven (the son left God and blamed it on God abandoning him even though he did it to himself), the "fall of man" (the separation) etc. It's all there in the course. It was just somewhat mis-described in the bible, but based on the same facts.

"The Garden of Eden, which is described as a literal garden in the Bible, was not originally an actual garden at all. It was merely a mental state of complete need-lack. Even in the literal account, it is noteworthy that the pre-Separation state was essentially one in which man needed nothing. The Tree of Knowledge, again an overly-literal concept, (as is clearly shown by the subsequent reference to "eating of the fruit of the tree") is a symbolic reference to some of the misuses of knowledge referred to in the section immediately preceding this one. "

"This section is inserted here because it deals with a more fundamental misuse of knowledge, referred to in the Bible as the cause of the Fall (or Separation)."

"We have discussed the fall or Separation before, but its meaning must be clearly understood, without symbols. The Separation is NOT symbolic. It is an order of reality, or a system of thought that is PERFECTLY real in time, though not in Eternity. All beliefs are real to the believer.""Until the Separation, which is a better term than the Fall, nothing was lacking. This meant that man had no needs at all. If he had not deprived himself, he would never have experienced them. "

"When the "lies of the serpent" were introduced, they were specifically called lies because they are not true. When man listened, all he heard was untruth. He does not have to continue to believe what is not true, unless he chooses to do so. All of his miscreations can disappear in the well known "twinkling of an eye", because it is a visual misperception. "