i think if his thesis is to be taken seriously, it should be generalized to the idea that working together may have been a dominant factor. but, i mean, humans aren't unique in our tabula rasa at birth - essentially all advanced mammals rely on taught behaviour rather than instinct. is designing a stone age tool any more complicated than designing a hunt of a gazelle? i mean, how are they co-ordinating that, anyways? the lions need to watch and learn and understand and repeat....
so, it may have been a factor, i'll grant the point. but, i don't find the idea that it's the dominant stimulus to be compelling.
that said, i agree that the definition of language as a generative grammar is a little too restricted. i mean, we realize today that our brains are more like quantum computers than turing machines, so this idea that our brains have to work something like a recursive grammar (because they're computers.) is probably superseded. but, it's still interesting to wonder if there's something to the idea of our brains approximating turing machines, and that having something to do with the ubiquity of recursion in human language.
but, if that's true, it seems to be unique, or almost so, as no other species communicates that way.
so, we should get over our arrogance around the point and expand the definition of language to include birds tweeting, elephants rumbling, dolphins crying and, yes, dogs howling, too.