But there is *much* more to the myth than the simple assertion that there was, at some time in human history, a single language. Who knows? Maybe there was. Maybe in the depths of history, there was a unified proto-language of some kind spoken by a human ancestor. I'm not a linguist, so I won't speculate beyond the myth.
To me, it seems that you need some kind of divine intervention to bring about a scenario without a common ancestral tongue. The alternative seems to be humans without language spreading over the earth, and then independently creating languages afterwards. This suggests the potential for language was already there, but never expressed until after spreading across the globe.
Of course, that doesn't mean trying to locate the signs of an ancient Ur-tongue isn't a pointless waste of time. Polish and English are two completely different languages, even though their common ancestral tongue is believed to have been spoken only 3,000-4,000 years ago. This period has seen the rise of large, settled societies; the advent of writing, the influence of common lingua frances like Latin and ever increasing communication and travel within and between the two language communities - all factors which should alow their divergence from one another.
To think, then, that any trace of connection would remain between two languages seperated by tens of thousands of years, mostly spoken by small, close-knit societies with minimal contact with outsiders and no written language, is absurd.
Please tell me to shut up if I'm going off topic here!