Language began 70,000 or more years ago. We can reconstruct languages with moderate assurance only about one-tenth that far, and most languages much less than that. To the mainstream linguist, Ruhlen’s claim of showing that current languages are all related back through that first one requires that he speculate about 90% of the possible data, nearly all of which is irrecoverable.
To take a geographic analogy, Ruhlen is claiming
All roads lead to Rome, or something like Rome.
The other linguists counter
We can only with great effort trace these roads into the next town, and very occasionally, the next country. Roads do tricky things. Sometimes a freeway dwindles down to a cowpath. Sometimes the cowpaths disappear altogether. Roads take unexpected turns and switchbacks. It is fantasy to assert that all roads lead to Rome.
There is not much way around the fact that the mainstream linguists have a very powerful argument here. A lot of intelligence and effort has gone into tracing languages even short distances in time. Ruhlen’s counterclaim that he is using different techniques, that he is flying over the area in a balloon rather than examining the ground, is somewhat effectively countered with the rejoinder “there’s a lot you can only see from the ground.”
Nonetheless, I think Ruhlen’s theory will eventually prove out. The nature of the arguments used by his opponents fall short of objective scientific inquiry in many cases. There are a few good arguments, two of which are noted above. But the bulk of the arguments actually used are not so rational. When smart people resort often to poor arguments, something is up.
Ruhlen’s mentor, Greenberg, proposed a larger grouping of African languages which was similarly rejected when it first came out. That ridiculed theory is now generally accepted. Greenberg proposed a larger grouping of Native American languages that was rejected when it first came out. There is now some grudging acceptance of it as at least possible. The strongest parts of that argument, the recurrent na, ma, for I, you, and tina, tuna, tana for son, daughter, child, have not been adequately refuted. The argument that such coincidences could be accidental, given so many hundreds of languages, is struck down by the inconvenient fact that it has in fact, not happened elsewhere. Third, Greenberg’s grouping of Eurasiatic, tying together Indo-European, Uralic, Semitic, and other families, is frequently countered by a patently stupid argument. Because the Nostraticists clump several families together as a European-Asian group and Greenberg proposes a slightly different grouping, the theory is dismissed because these linguists with highly similar theories cannot exactly agree what the categories should be though the overlap is great. Next, Greenberg and the Nostraticists made mistakes -- precisely the mistakes that a generalist, overview type of scholar would make.
There is one huge new fact, and it is being ignored. True, it was first published in an obscurer journal – Ruhlen is not published in the better ones – but there is not even any curiosity about the claim. I have myself pointed it out to linguists who have dismissed it with no more than “Oh. Ruhlen. I wouldn’t recommend you pay much attention to that.” The new fact is that Kusunda, a Nepalese language previously categorized with the languages near it, is claimed to actually be an Indo-Pacific language. To those of us far away from the area and controversy, this would seem a small claim. But for Kusunda to be related to the languages on Papua New Guinea is not possible given our current understanding of the movements of people. To be related, those peoples would have had to have been in contact at least 50,000 years ago. That is more than 8 times the current greatest time-depth acknowledged for language connections. It is nearly all the way back to the beginning of languages.
Is Kusunda indeed related to the languages in New Guinea? I have not remotely the training in linguistics to tell. Either side could convince me in fifteen minutes. But I find it damning that there is now curiosity.
Next, I will speculate why Ruhlen attracts such hatred.