This is an important post, and I encourage everyone to read it.
The first story is the most technical, and it is about sole-genetic progenitorship (discussion). If Adam and Eve were more ancient than 500-700 thousand years ago, they could have been our sole- genetic progenitors. This would mean all “humans” would descend directly from Adam and Eve, and their offspring never interbred with others.
The second story is the most recent, and it is about genetic-interbreeding progenitorship (discussion). If Adam and Eve were about 200 thousand years ago, it might be possible they were the genetic progenitors of Homo sapiens , as long as their offspring interbred with other hominids like Neanderthals. This finding is not settled yet , and will be looked at more closely with Reasons to Believe this Fall
The third story is the most surprising, and it is about sole-genealogical progenitorship (discussion). As recently as 6,000 years ago, Adam and Eve could have been created de novo, in the Middle East, ancestors of us all. Their offspring, however, would have interbred extensively with those outside the The Garden. This is The Genealogical Adam we have been putting forward for over a year now.
The Three Stories are discussed separately on these threads: