Cain's Wife - Literal Inerrancy of Genesis
So the basis of this post is the teaching that the only way that the earth could have been populated was for the children of Adam and Eve to marry each other. God would have protected them from the consequences of this intermarriage so that the human race could be propagated.
It is defined Church teaching that all humans are descended from the single pair, Adam and Eve.
The Papal Encyclical of Pope Pius XII Humani Generis, promulgated in 1950 teaches that the question of the origin of the human body is open to research by natural scientists and theologians. The pope insists on the careful weighing of the pros and cons of the grounds for its origination from an already living material, and warns the faithful against the assumption that discoveries up to the present determine and prove the origin of the human body from an organic stuff, and points out that in this question, the need for the greatest reserve and care emerges from the sources of revelation.
Pope Pius is quite clear about the reality of Adam:
37. 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 that either after Adam there existed on this earth true men who did not take their origin through natural generation from him as from the first parent 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 with that which the sources of revealed truth and the documents of the Teaching Authority of the Church propose with regard to original sin, which proceeds from a sin actually committed by an individual Adam and which, through generation, is passed on to all and is in everyone as his own.This statement addresses the Pre-Adamite Theory first expounded by the Calvinist Isaac de la Peyrère in 1655 and the view of a number of contemporary scientists who held that the various races were derived from several separated stems (a theory termed polygenism). Against this idea, the Church teaches that the first human beings, Adam and Eve, are the proginitors of the whole human race (monogenism). This teaching is not a dogma, but it is a necesary pre-supposition of the dogma of Original Sin and Redemption.
Pope Pius goes on to affirm that there is a degree of historicity in the Genesis account:
38. ...the first eleven chapters of Genesis, although properly speaking not conforming to the historical method used by the best Greek and Latin writers or by competent authors of our time, do nevertheless pertain to history in a true sense, which however must be further studied and determined by exegetes; the same chapters, (the Letter points out), in simple and metaphorical language adapted to the mentality of a people but little cultured, both state the principal truths which are fundamental for our salvation, and also give a popular description of the origin of the human race and the chosen people.
The "Letter" Pope Pius XII refers to is a letter sent to the Archbishop of Paris by the Pontifical Commission on Biblical Studies (you can read the whole thing here). The most pertinent passage is perhaps this one:
The question of the literary forms of Genesis...is, the Commission declares, a much more obscure and complex one, these literary forms are quite unlike those of classical or modern literature. Hence one cannot deny or affirm the historical character, en bloc, of these chapters, without forcing them into categories to which they do not belong. We may concede that they do not contain history in the classical or modern sense, but the state of our knowledge at present is not such as to, allow us to give a positive solution to the problems they set. Further study is necessary.
To state simply that these narratives do not contain history as we know it, might easily give the impression that they do not contain history in any sense-whereas they do in fact relate in simple and figurative language adapted to uncultured minds the fundamental truths that underlie the "economy of salvation" and give a popular description of the origins of the human race and the Chosen People.
The letter does leave room for development of our understanding, yet there is a prominent movement in some Christian circles to take Genesis literally. Here's an example of how biblical literalists deal with one obvious problem: where did Cain's wife come from?
As Pope Pius XII points out in his encyclical, there is a great temptation to capitulate traditional understandings to appear more reasonable; to accept received opinion, but we have a duty to be thorough in our analysis and have some faith in what has been handed down to us by Sacred Scripture.
Sometimes attempts like the good pastor above's can appear torturous. Ultimately, can we know? We can discover some truths about the origins of humanity, but will we ever know? I have always held that Genesis is a book about WHY God made humanity, not HOW He did it.
To back this up, it is worth noting that Genesis has always been read by the greatest theologians in history as being primarily allegorical. St Augustine in his Commentary on Genesis speaks about how it is foolish to read Genesis as a scientific account. In his text entitled The Literal Meaning of Genesis, in it, Augustine argues that the first two chapters of Genesis are written to suit the understanding of the people at that time. In order to communicate in a way that all people could understand, the creation story was told in a simpler, allegorical fashion. Augustine also believed God created the world with the capacity to develop, a view that is harmonious with biological evolution. St Jerome talks about how Genesis is written in the literary style of "myth".
Origen of Alexandria in his commentary on Genesis speaks about how it would foolish to presume there was a literal Garden. Origen, a third-century philosopher and theologian from Alexandria, Egypt—one of the great intellectual centres of the ancient world—provides an example of early Christian thought on creation.
Origen presented the main doctrines of Christianity and defended them against pagan accusations. He opposed the idea that the creation story should be interpreted as a literal and historical account of how God created the world. And there were other voices before Origen who advocated more symbolic interpretations of the creation story. Origen’s views were also influential for other early church thinkers who came after him. Even St Thomas Aquinas warns against reading the Bible or Genesis in a way that contradicts reason or natural philosophy.
Bishop Barron puts it this way: Genesis is not a nascent attempt at science in the way that many world religions used myth to explain the things they saw and experienced in the natural world around them, rather it is exquisite theology.
Even more impressive, the geneticists concluded that every person on Earth right now can trace his or her lineage back to a single common female ancestor who lived around 200,000 years ago. Because one entire branch of human lineage is of African origin and the other contains African lineage as well, the study's authors concluded Africa is the place where this woman lived.
At the time of Humani Generis, polygenism was the prevalent scientific theory, this has since been overturned and monogenism proven to be correct.
I don't think we can ever "prove" how humanity began, but it is fascinating to think about. As Catholics, I think we should not fear the science, it reveals God's fingerprints, but we need to focus on the exquisite theology of Genesis, which remains one of the most fascinating books of the Bible and one that absolutely fascinates me still.