From a Catholic Answers tract:
"The argument is that all of this is real history, it is simply ordered topically rather than chronologically, and the ancient audience of Genesis, it is argued, would have understood it as such.
"Even if Genesis 1 records God’s work in a topical fashion, it still records God’s work—things God really did.
"The Catechism explains that “Scripture presents the work of the Creator symbolically as a succession of six days of divine ‘work,’ concluded by the ‘rest’ of the seventh day” (CCC 337), but “nothing exists that does not owe its existence to God the Creator. The world began when God’s word drew it out of nothingness; all existent beings, all of nature, and all human history is rooted in this primordial event, the very genesis by which the world was constituted and time begun” (CCC 338).
"It is impossible to dismiss the events of Genesis 1 as a mere legend. They are accounts of real history, even if they are told in a style of historical writing that Westerners do not typically use.
"Adam and Eve: Real People
"It is equally impermissible to dismiss the story of Adam and Eve and the fall (Gen. 2–3) as a fiction. A question often raised in this context is whether the human race descended from an original pair of two human beings (a teaching known as monogenism) or a pool of early human couples (a teaching known as polygenism).
"In this regard, Pope Pius XII stated: “When, however, there is question of another conjectural opinion, namely polygenism, the children of the Church by no means enjoy such liberty. For the faithful cannot embrace that opinion which maintains either that after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parents of all, or that Adam represents a certain number of first parents. Now, it is in no way apparent how such an opinion can be reconciled that which the sources of revealed truth and the documents of the teaching authority of the Church proposed with regard to original sin which proceeds from a sin actually committed by an individual Adam in which through generation is passed onto all and is in everyone as his own” (Humani Generis 37).
“The story of the creation and fall of man is a true one, even if not written entirely according to modern literary techniques. The Catechism states, “The account of the fall in Genesis 3 uses figurative language, but affirms a primeval event, a deed that took place at the beginning of the history of man. Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents” (CCC 390).”
Hope this helps,