I would really like to know when and how did the first oral language develop.
What seems obvious to me is that upon the beginning of the Neolithic Era (~10,000b.C.), when the establishment of farming, pottery and animal domestication seemingly commenced, people must have already been using an oral language. Otherwise, the formation of communities would have been impossible.
Regarding script, the following paragraph seems to me valid :
"The most widespread group of languages today is the Indo-European, spoken by half the world's population. This entire group, ranging from Hindi and Persian to Norwegian and English, is believed to descend from the language of a tribe of nomads roaming the plains of eastern Europe and western Asia (in modern terms centring on the Ukraine) as recently as about 3000 BC. "
from :
http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ab13