evolution of language timing*
6-8 MYA  -last common homo Sapiens and chimp ancestor
4 MYA -- earliest known bipedal- chimp-sized brain, body
2.0 MYA-- last common chimp and bonobo common ancestor**
2 MYA--   systematic toolmakers, homo Habilis
1.5 MYA- rapid increase in homo X relative and absolute brain size
.8 to .1 MYA--  modern humans emerge from Africa
  increasing adaptations for human language
  >> brain size (400cc up to 1500 cc)
cerebral asymmetry- hand & brain
genetic changes  in human brain circuitry, e.g FOXP2, CNTNAP2.
development of modern vocal tract
.1MYA-- earliest modern human fossils
.1 to .03 MYA  --large-brained Neanderthal dying off
.035 MYA  --  early representations widespread (artifacts)
little info on chimp/bonobo branch over this time period
5000 human dialects emerge as humans populate earth
writing develops about 5000 years ago.

NOTES
* dates are approximate needless to say
** We humans cannot be descendants of chimps; we are their cousins.  Darwin believed-- accurately in light of recent evidence of fossils and DNA-- that humans evolved in Africa and that chimps and gorillas were relatives (but not our ancestors.)
" On the Birthplace and Antiquity of Man.- We are naturally led to enquire, where was the birthplace of man at that stage of descent when our progenitors diverged from the catarhine* stock? The fact that they belonged to the stock clearly shews that they inhabited the Old World; but not Australia nor any oceanic island, as we may infer from the laws of geographical distribution. In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere. (Ch.6, Descent of Man, 1871)"