Huh?
Just go into the alternate universe where perhaps the Bible is true for a second.
Adam and Eve are the first people. It was “incest” for quite a while.
Interesting question, though I did think it through historically — I need to do a concordance search on the Hebrew. Interesting problem. Leviticus is where it is mentioned without cracking open a Bible. Chapter 18. Infamous text that Paul also refers to with Peter in the New Testament.
You posted, in part: Adam and Eve are the first people. It was “incest” for quite a while.
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Perhaps there was incest, but I also seem to recall that after Cain killed Abel he left to go live in some town or city somewhere else. If God made Adam and Eve, I guess He could have made some more humans later on, just as He probably made more than two of each species, assuming that Genesis has factual instead of purely symbolic meaning.
I am fully aware of the implications of Adam and Eve...that is why I do not believe the Creation story literally. There are far too many contradictions.