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? 1. Adam and Eve's progeny mated with descendants from another lineage that the Bible (through no apparent malice) failed to describe. 2. 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.