I didn't expect John Hawks to answer me so quickly (emphases mine):
... we have undergone light-years of change since the last Neandertals lived. This is not a question of "modern human origins" anymore. We can now show that living people are much more different from early modern humans than any differences between Neandertals and other contemporary peoples. I think that "modern humans" is on its way to obsolescence. What matters is the pattern of change across all populations. Possibly that pattern was initiated by changes in one region but the subsequent changes were so vast that the beginning point hardly matters... [From John Hawks Anthropology Weblog : 2007 10]Most of the popular books on human origins I've read emphasize how similar we are to Homo sapiens of 60,000 years ago. It appears that meme is on its last legs. We look a lot like our ancestors, but our minds are very different.
To answer my original question -- Home sapiens spent the last 115,000 years turning into an animal that could write. It wasn't easy.
It's tempting to suggest we need to name a new human "species" that was launched 15,000 years ago, but these arbitrary demarcations are increasingly unconvincing, just as misleading as the concept of "the modern human".
The more we learn about the evolution of the human mind the more fluid it seems. Our modern world has many more niches for exotic minds than the ancient world; if we live long enough we'll fill those niches.
One day we might need interlocutors -- even between speakers of the same language.
The rest of Hawks article is well worth a close read. He uses a recent discovery from the Neandertal genome to support a favorite thesis of his -- that we are part Neandertal.