Answer by Balaji Viswanathan:
Origin of language is one of the most mysterious things. There are dozens of speculative theories for this. Here is a short summary of those theories:
There are two schools of thought:
Continuity school: Our language evolved from earlier primates. We mimicked the various sounds around us and also mimicked the muscular movements to produce sounds connected with emotions. For instance, in my language "kaka" mean crow because the crow sounds are heard like "ka ka".
Discontinuity school: Noam Chomsky and a few others believe that there must have been a random mutation 100K years ago that suddenly made us discover languages.
Broad distribution of language families.
Origins of Grammar
The history of grammar is far more recent than language. For thousands of years, humans communicated just fine. If you cry that there is a lion around you, there is lion around you. There is nothing ambiguous about it. There was no need of complex rules.
However, as our civilization started growing, complex ideas started evolving and without the use of the right form, things can get confusing. The concept Grammar first evolved in Sanskrit withand leading the way in 4th-6th centuries BC. One idea is that these people were purists and wanted to have a really refined language that separated them from the plebians. In any case, the study of Sanskrit became a serious part of the ancient .
Other parts of India quickly followed. Around that period,– a landmark work on Tamil Grammar was written in 3rd century BC.
After about 1000 years, the concept of grammar spread to Arabia and from there it spread to Europe. Initially, Grammar was placed into the "trivium" – the basic things people have to learn at a University (along with logic and rhetoric).