re:If somehow a group of 6-months-olds could be left completely on their own, I would predict that by 12 months at least some meaningful sounds would have developed and that by 18 months they would have a rudimentary vocal language of some kind. At least the equivalents of I'm hungry, I'm hurt, check this out, and hey, that's mine!


twins have been known to do it... most of them drop their private language by age 5, but there is a famous case of twins who persisited in 'speaking their own language well into their teens..

as they got older the vocabulary stole shamelessly from english, but the rules of 'grammar' differed, (but were rather consistant)