Outside of certain self-consciously entrenched and/or conservative theological quarters, the notion of a historical "fall" into sin on the part of humanity is, to put it mildly, out of fashion. Even for those who want to identify a theologically sophisticated way of locating some "first" set or pair or community of identifiable human beings in the evolutionary tree, and so open a way to understand some kind of "fall" in their communal life together, do not -- so far as I know -- imagine a prior created order full of unmitigated bliss matched by an absence of sickness, biological death, and the like.
Thus, what seems to be most broadly assumed, for those seeking to remain within traditional ecumenical theological claims -- particularly having to do with sin's universality and its systemic deep-rootedness -- is that, in Kierkegaard's words, "sin posits itself." As David Kelsey expands on the phrase and on the concept, "original sin" is an acceptable term so long as it serves explanatory, not (what he calls) "genetic," purposes. (As it happens, I often misremember this latter term as "genital" -- which, in a real sense, identifies the traditional theme quite well in its own way.) That is, original sin names the condition of human being; whatever caused sin in the first place or causes sin at all is nothing for the doctrine to answer: as surd, as shadow of that which is good, there is nothing either to explain or to discover the origin of. It is simply there; it posits itself. In its very lack of origin and meaning it carries its essence as sheer negative, as death-dealing shatterer of meanings.
All this is well and good, but my sense is that the consensus mistakes a part for the whole. To be sure, one emphasis within the traditional "genetic" accounts of (original) sin was to find some explanation, some origin, some founding event that would help to make sense of how sin could be present -- seemingly omnipresent -- in a world Christians have always claimed God created good and without sin. On one side, it is an apologetic move, attempting to answer challenges from the outside; but it is also a catechetical move, seeking to find a way to raise up disciples who know that God is not the author of sin. So even if "finding a reason for sin" was inevitably a fool's errand, the attempt nevertheless does make sense on a number of accounts.
But the "search for a meaningful explanation" of sin is not the entirety of the "genetic" account. There is also what we might call the narratival aspect, and this is what contemporary theologians seem to elide or even to forget. In short, "the fall of man" was not merely a piece in a larger conceptual puzzle about God and human creation; it was also, perhaps even more so, a stage in the story of God and the world. Hence the great moments in the traditional theological narrative: creation, fall, redemption, glory. Yet in taking away anything like an identifiable (read: story-tell-able) event of humanity's falling into sin in the gospel story of God and God's creation, theologians, thinking they were being faithful to the historical record as well as amending a well-meant but wrongheaded philosophical predilection, have in fact swept the feet out from underneath the church's ability to proclaim a coherent salvific narrative.
Unfortunately (and unsurprisingly), I have no quick remedy for this situation. I am as baffled as any other Christian desiring to be faithful both to history (evolutionary biology; no pre-fall idyllic creation sans disease and death) and to the gospel story (a good creation; God not authoring sin; nevertheless: sin; God in Christ forgiving sin and reconciling sinners) as to how to fit the pieces together. However, I am convinced that we shouldn't leave the two apart, much less splice them up for separate discourses; and, moreover, that we can't just leave it at "sin posits itself," lest we abandon storytelling in missional, apologetic, and catechetical proclamation. I for one think this particular plot point to be too important to give up without further critical reflection; nor does it seem at all unripe for creative reformulation today.
The challenge, therefore: How might Christian theologians go about reformulating the doctrine of (original) sin, all the while remaining faithful to the essential plot points of the gospel story, including humanity's being created good yet proving sinful, without indicting God as the author of sin (and so proposing a creation created good-and-sinful), and simultaneously keeping true to the historical record?