Did Adam and Eve's Progeny Commit Incest? I have a multi-part question.


Did Adam and Eve's Progeny Commit Incest?


Genesis, Chapter 4 tells us about Cain and Abel.
Genesis, Chapter 5 tells us about Seth and "other sons and daughters".

I highly doubt that our species began with many acts of incest (not just for religious/legal/moral reasons but biological reasons as well), so how did humanity continue?

As a Christian, am I obliged to accept one of the following?


Adam and Eve's progeny mated with descendants from another lineage that the Bible (through no apparent malice) failed to describe.
The story of Adam and Eve is just that - A story. It is a story that was passed down by way of oral tradition. It was never meant to describe actual historical events.
There is a third option - 

The prohibition on incest didn't come about until the covenant in Leviticus &amp; Deuteronomy, and to accuse Cain, Abel, and Seth of incest is to accuse them ex post facto.

As an aside, a Young Earth Creationist would date the Creation to 4004 BC, and the Exodus (and  hence the Covenant) to about 1440BC.  As such, you would be accusing them of a crime that wasn't mandated for nearly 2600 years.

If you want to say, "but surely the law goes back further than the covenant," you get into territory of, "So when did it become a law?"  Incest is prohibited in most secular cultures today because it weakens the gene pool.  Over time, the level of closeness has gotten wider in order to ensure a wider mixing.  In modern times, a first or second cousin is off-limits.  If I remember correctly in Leviticus, immediate family was prohibited, but I believe that cousins were ok. If you follow the trajectory backwards, you'd probably arrive at a date at which it was ok even for family members to procreate together, societally speaking.



An objection has been raised worth noting:


  regardless, biology hasn't changed. legally incest wasn't "wrong" yet but humanity does not tend to survive well on inbreeding. 


My response stands, however:


  Agreed that humanity doesn't tend to survive well on inbreeding, but it fares even more poorly if the first of the species refrain from procreation altogether