The recent messages on the subject of AIT have run so far afield that I find that even I, a historian and lawyer by training and profession, may have something useful to contribute.
 
I say "may" because it is not at all clear that the List welcomes historians or attorneys.  The "scope" definition of the List includes "historians, and others interested in any aspect of Indological studies" in its ambit, but largely cancels this out by proscribing "discussions about Indian history and culture."
 
First, even were it preferred that the List be purely about language, it could not help but be about Indian history and culture also.  What meaning do the words of the Rg Veda have except in terms of Indian history and culture?  How can a linguist discern the meaning of ancient words without an understanding and appreciation of history and culture?  The AIT theories (including both the inward and outward migrationist views) are legitimate grist for this forum; how can one hope to interpret the RV accurately without some grasp of what actually occurred historically?
 
Second, many of the scholars posting here recently could use some cross-field training in the principles of evidence and proof of facts.  The degree of certitude exhibited seems inversely proportional to the quality of the evidence offered in proof.  There is a legal maxim that one should never describe anything as "clear" or "clearly proven," for it will instantly alert the judge to a weak point in one's case: one has need of such persuasive language only when the evidence for that point is weak.  Since AIT (I refer to both the inward and outward versions each time) is not yet susceptible of hard proof, one way or the other, a little humility/reasonableness in the language employed in advocating one view or the other would be appropriate.  The evidence will support hypotheses, theories, inferences, possibilities, even probabilities, perhaps, but not the doctrinaire certitude some have espoused.
 
Third, scholars ought to be able to distinguish between the important and the trivial.  Regrettably, much of the content of recent discussion has revolved around the trivial.  Insults, misquotations, editor's errors of attribution, are debated as though this actually proved something important.  Arguments that depend on the psychological effect of a rhetorical victory in a trivial matter are inherently suspect: it requires, at the least, some showing of why debating trivia is material to and productive of something important.  The rule of relevance, in other words.  Sorry, I don't see that those who have engaged in such debate have met that burden.
 
Fourth, the date of the RV seems pretty important to me, for consequences, both linguistic and historical, flow from the dating.  The date of the Buddha, internal points of linguistics, archeology, each may have something relevant to contribute.  Yet, speaking as a historian and lawyer, some of the most accessible evidence is being regularly ignored: the story told by the RV itself.  I concede that it is subject to the criticism that the RV is myth, not history, and edited and reedited myth, at that, but it remains the best, the only, document purporting to be from the period of the AIT (both, etc.).  It, together with some other sources, tells a story in which Aryan groups, seeing the rich and defenseless North Indian plains and rivers, initially subjugate, expel, exterminate, and plunder the darker indigenous occupants.  Later, after contacts over time measured perhaps in centuries, a detonate of sorts occurs, individually and politically, and, still later, religiously.  They learn each other's languages, they intermarry, they form alliances, and eventually they adopt a religious compromise or consensus in which some indigenous gods (Siva, par excellence) are recognized and given major status, some indigenous and foreign gods are amalgamated and interpreted to be one and the same, and some indigenous elites are elevated to Aryan social status (notably, brahmanic status), which elites, as the price of co-option and peace, adopt the Aryan view that the lowest of the low, the dark-skinned "serfs" or "outcastes," remain deservedly at the bottom of the social and moral order. 
 
This story has been dismissed as irrelevant and fanciful by those who prefer their scholarship untainted by any contact with myth, but since it is the only extant voice of the past, its version of events (if accurately described), must be tested against other evidence.  It seems to me that the out-of-India AIT proponents have not yet come to grips with their own history as described in one of the documentary sources they most revere, the Rg Veda.  (It may be noted that the story it tells ends ultimately in a victory of the indigenous peoples, of sorts; they persisted and amalgamated the Aryan into their own structure; but at such a price to those who were left out of the bargain.)
 
Fifth, two items of "hard" evidence exist which require explanation by those who doubt the indigenous contribution to the RV.  (1)  The Mohenjodaro seal that shows what can only be a Prajapati figure.  It exists; the items and emblems are unique to Prajapati and Siva and cannot reasonably be dismissed as a curious coincidence; their antiquity at least predates the customary dates for the redacted Rig Veda; it implies the indigenous IVC had a religious view that was at least in this part very similar to later Hindu beliefs.  If some of this shows up as part of the RV, which otherwise is thought to be an Aryan document, how did it get there?  If it shows up only in later texts, where was it in the interim described by the RV? (2)  The Saraswati river and the cities that existed along its banks.  The RV celebrates this river; apparently "Aryan" segments treat it as the fairest, most preeminent of rivers.  Geological evidence has established that the river did exist, but ceased to flow, probably in stages, over a period of centuries that predates the received date of the RV.  But cities existed along it, as archeologists have documented, and the cities would have had no particular reason to exist there unless the river remained a source of water and commerce at that time; meager, perhaps, but nonetheless sufficient for small cities and towns.  And cities can be dated, and the dates offered thus far by archeologists (very few, in a very few localities, and not generally along the Saraswati) yield dates older than the received RV date by many centuries, sometimes millennia.  If the RV regards the river as real (as it appears to do), then the RV must have been formed, at least in part, during the period when water ran in the river.
 
It seems to me that the RV likely is a collection of ancient sources, much like the Bible, some dating through oral history to dates far older than the redacted versions, and some dating to later periods.
 
Do the linguists studying the texts perceive such an assemblage?  If so, what efforts and success has been made in sorting it out?
 
I return to lurking.
 
David Salmon