Following a link from this blog, it took me to this entry about why Adam should be considered to have been a real, historical person.
1. On the face of it, the basic literary genre of Genesis 1-4 is that of historical narrative (as opposed to, e.g., poetry, legal code, or apocalypse). This isn’t to say that these chapters can contain no figurative language; many conservative OT scholars would readily grant that they do. But it does imply that these chapters (like the rest of Genesis) are intended by the author to report important events within historical space-time. As such, there should be a strong presumption that the Adam of chapters 1-4 is no less a real historic figure than, say, the Abraham of chapters 12-25.
8. In Romans 5:12-21, Paul draws his famous parallel between Adam and Jesus. The transgression of “one man” (Adam) brought judgment and death, but the obedience of “one man” (Jesus) brought righteousness and life. If Adam never actually existed (never mind sinned), Paul’s parallel — on which his theological argument depends — falls flat.
I can recommend it, it puts paid to many of the assumptions liberals and emergents operate under.