I know this is an immensely significant topic, and I hope you'll not be offended that I still have a very different view. It would seem then that the justification for a literal Adam lies wholly in a theological view and that all these discussions of anthropology are merely an effort to find support for that view rather than reflect on the meaning of anthopological findings in their own right. I think these concepts should be re-examined in the light of anthropology and psychology, not defended in one narrow traditional interpretation despite the wealth of new understanding available. It reminds me of the Mormon doctrine of pre-existence.
Biblical methods are obviously also at issue.
To answer Jim, I seriously doubt that Moses really wrote the Pentateuch since it contains the record of his death. Clearly, none of the authors of the Bible thought they were taking dictation. Jesus would've naturally spoken of the Genesis accounts as true because this was the view of his day, not because He had a Revelation about the Origin of early man. The passage Jim quoted in Romans is no doubt the closest the Bible comes to affirming a substitutionary theory of atonement. Certainly it was the one I considered most before I changed my mind.