What's it an allegory of? What were the Bible writers allegorizing? Allegory, like metaphor and simile, is a literary form that uses substitution. What were they symbolizing with Adam and Eve. Nothing that they could have known anything about.
An allegory is a story, poem, or picture that can be interpreted to reveal a hidden meaning, typically a moral or political one.
No, I do not think that people living at the time the Bible was recorded could have known what those symbols meant, since the Book was intended to be 'closed up and sealed' till the time of the end.
Daniel Chapter 12:8 And I heard, but I understood not: then said I, O my Lord, what shall be the end of these things? 9 And he said, Go thy way, Daniel: for the words are closed up and sealed till the time of the end. 12 Blessed is he that waiteth, and cometh to the thousand three hundred and five and thirty days. 13 But go thou thy way till the end be; for thou shalt rest, and stand in thy lot at the end of the days.
The time of the end came when Baha'u'llah appeared at the end of the days and He unsealed the hidden meanings contained in the Bible.
I believe that the story of Adam and Eve is an allegory, not a true story. I believe that the story of Adam and Eve who ate from the tree, and their expulsion from Paradise is a symbol. The story contains divine mysteries and universal meanings, and it is capable of many explanations.
I believe that there was a real man called Adam and that He was the first Prophet of the Adamic Cycle of religion. I also believe we inherited the sins of Adam, but not because he ate an apple from a tree. This is how I believe the descendants of Adam inherited the sins of Adam:
“For the spirit and the soul of Adam, when they were attached to the human world, passed from the world of freedom into the world of bondage, and His descendants continued in bondage. This attachment of the soul and spirit to the human world, which is sin, was inherited by the descendants of Adam, and is the serpent which is always in the midst of, and at enmity with, the spirits and the descendants of Adam. That enmity continues and endures. For attachment to the world has become the cause of the bondage of spirits, and this bondage is identical with sin, which has been transmitted from Adam to His posterity. It is because of this attachment that men have been deprived of essential spirituality and exalted position.”
In sum, the meaning of the serpent is attachment to the human world. This attachment of the spirit to the human world led the soul and spirit of Adam from the world of freedom to the world of bondage and caused Him to turn from the Kingdom of God to the human world. When the soul and spirit of Adam entered the human world, He came out from the paradise of freedom and fell into the world of bondage. From the height of purity and absolute goodness, He entered into the world of good and evil.
The full explanation of what I believe about the allegory is in this chapter:
30: ADAM AND EVE