I don't know whether this is an appropriate place to submit this question. If this is not the right place, I apologize.
Now the question:
I was reading Rousseau's Discourse on the Origin of Inequality when I came across this passage in the text:
[on the development of language] The first [question] that presents itself is to imagine how languages could be necessary; for since men had no communication among themselves nor any need of it, I fail to see either the necessity of this invention or its possibility, if it were not indispensable. I might well say, as do many others, that languages were born in the domestic intercourse among fathers, mothers and children. But aside from the fact that this would not resolve the difficulties, it would make the mistake of those who, reasoning from the state of nature, intrude into it ideas taken from society.
[interlude on how it was just natural for men and women to live isolated from one another and how nomadic "savage people" were]
It should […] be noted that, since the child had all his needs to explain and consequently more things to say to the mother than the mother to the child, it is the child who much make the greatest effort toward inventing a language […]
Now, I don't know if it is bad history or not. But now I want to know:
That's one of the basic questions of linguistics, and the answer is no one really knows. Try asking /r/linguistics and you will receive a plenty of various theories.
In an effort to try and determine the original primordial need for language, one method social scientists believe may be useful is conversational anaylsis.
There have been studies where anthropologists sit and secretly listen to people having conversations in public places. The subjects of these conversations were noted as was the amount of time spent on a given topic. Unsurprisingly, conversation analysis found gossip, talking about other people, is by far the dominate topic of conversation making up well over 80 percent of a given conversation.
This observation has been made in different cultures in different places leading some to conclude language was possibly created to determine an individual's place in society.
Conversation constitutes the primordial use of language, according to Charles Goodwin at the University of South Carolina Anthropology Department. Language is the central medium of socialization. Social interaction with language is the primary means through which the business of the social world is conducted, the indenties of the social group are affirmed or denied, and cultures are renewed, affirmed or modified.
If past humans are like modern humans, it is possible language was first developed and used, as today, to learn about others in the group and determine dominance and avoid conflict.