Well, even though it is Sunday, Praise talked me into adding my two cents worth to this thread. Probably will pi** a lot of folks off, but here goes.
Scholars all generally concede that the Book Genesis is prehistory, and they generally regard it using a ten-dollar theological term: Genesis is an etiological mythology. An example of this treatment of Genesis can be found by a foremost scholar in the field. Gerhardt von Rad wrote what many consider the definitive word in the study of Genesis.
The gist of it, boiled down into layman's terms, is that there are powerful truths conveyed in the mythos of the stories of Genesis, but we would do well not to try to tax the thread of the storytellers by insisting on the total historical accuracy of their stories. And there are four definitive strains of storytellers to be found in Genesis: the Yahwistic, the Elohistic, the priestly, and the Deuteronomic. Sometimes their stories agree, and sometimes there are differences in their stories.
It was the Deuteronomists who redacted (or edited) the stories into one seamless narrative. So we tend not to notice right off that there are two creation stories, Genesis chapter 1 and Genesis Chapter two. We tend to get confused because there are also two versions of the stories of Noah and the Ark, and we don't tend to know enough about the epic of Gilgamesh to fully appreciate them anyway. Instead, we go looking for some silly old ark remains somewhere!
The gist of the idea is that the story of Cain and Abel is meant to answer the question about hatred for one's brother and murder. It addresses the issue about the quality of the sacrifice that each brother offered to God. It does not address the issue of their wives. (Sorry, ladies, the wives are not mentioned because they are unimportant to the story.) There is finally the idea that God does punish sin and murder, and so the story is an etiological mythology explaining that:
1. hatred between siblings exists in the world,
2. even if you hate your brother, murdering him is not a good idea,
3. there is an element of retributive justice before God who expects that we answer before him for what we have done, and
4. that we are indeed our brother's keeper---in that we do not live in splendid isolation, but we are intimately connected with one another in the family of man. (Kind of akin to John Donne's famous meditation, number 10 I think it was, "ask not for whom the bell tolls, it tolls for thee."
So in summary, there is much of value in Genesis, even if it is not generally regarded as history, as we regard history these days. And I don't mean to dismiss it as "well it is only a myth," unless of course you mean myth as Gerhardt von Rad defines myth, or Joseph Campbell does.