linguistics/ how do we recognize behaviours as communicative, and why is this important for the evolution of human communication

linguistics/ how do we recognize behaviours as communicative, and why is this important for the evolution of human communication
how do we recognize behaviours as communicative, and why is this important for the evolution of human communication?
the course is about evolutionary linguistics. the sources should be written within the essay. I mean you should mention the writer name and year after every information in the essay.