Language is possible due to a number of cognitive and physical characteristics that are unique to humans but none of which that are unique to language. Coming together they make language possible. But the fundamental building block of language is community. Humans are a social species more than any other, and in order to build a community, which for some reason humans have to do in order to live, we have to solve the communication problem. Language is the tool that was invented to solve that problem.
...one of the best definitions of human communication I have come across was made by a man who entered linguistics by way of a book that many believe was authored by a supernatural and super-powerful ape, the Bible. Daniel Everett, the man in question, began with something that deserves derision (learn the language of a Brazilian tribe for the purpose of translating a book about an all-knowing ape) and ended up with something that deserves consideration: A strong argument against Noam Chomsky's universal grammar—Indeed, "with indirection find direction." Everett, however, is a figure under heavy fire for reasons that do not seem unreasonable.