60.000 years ago - the Neanderthals
Studies of the skulls of Neanderthals (approximately 60,000 years ago) indicate that they would not have been capable of the full range of vowels used by modern humans. However, as pointed out by linguist Steven Pinker, a full range of vowels is not necessary for rudimentary speech. Even relatively complicated speech would be possible so long as a sufficient number of distinguishable consonants were in use.
According to Müller the thesis of a missing faculty of speech is unsustainable.
Further information and links:
"Sprache und Evolution" von Horst M. Müller; de Gruyter-Verlag; Berlin 1990