To know a language requires you to be able to be able to speak, read, write, and understand said language, while knowing about a language means that you know of its existence and possibly some facts...
The first is that people needed to work together during a hunt. They may have learned to talk so they can outsmart or trap animals. The second is that people learned to talk while helping each other...
If you mean, What theory is there about the origin of language, the answer is that there are many, many such theories, each with a funny little name. And each is probably right in its own little way,...
this may sound crazy but talking to aleins in different voices stimulates brain cell that control language and make the language your trying to learn faster