Proto-World and the Language Organ - very interesting article by Mark Rosenfelder about the development of language capability in the process of human evolution. It certainly seems far more likely that language is an emergent property of other cognitive abilities in the brain, rather than that there is a language organ in the brain. If there is no language organ, it seems logical to assume that there was no Proto-World language. However, there are many words in very widespread languages which are similar - but then it could be because of long-distance trade or something.
See also: How likely are chance resemblances between languages?