Language is defined as a system of communication. It uses arbitrary signals, such as voice sounds, gestures or written symbols. Language is far too complicated and intriguing to be explained.
The word Language can be used as a general concept about the specifically human capacity for acquiring and using complex systems of communication. It is is a particular kind of system for encoding and decoding information.( en.wikipedia.org/wiki/Language).Language is a cognitive process involved in producing and understanding linguistic communication. Its an expression through which knowledge belief and behavior can be explained and shared. In other way round, it’s a set of rules for generating speech.( http://www.nidcd.nih.gov/health/voice/whatis_vsl.html)
All social animals communicate but only humans have developed a language which is a set of prearranged signals. Human speech differs in a physical way from the communication of other animals. It comes from a cortical speech centre which does not respond instinctively, but organizes sounds and meanings on a rational basis. The section of brain is unique to humans.
When and how language developed is not possible to say. The origin of of human language will perhaps remain forever obscure. By contrast the origin of individual language has been the subject of very precise study over the past two centuries
That language is unique to humans; the answer seems obvious. Other animals communicate with a fixed repertoire of symbols but none appears to have combitorial rule system of human language. In which symbols are permuted into an unlimited set of combinations, each with a determined meaning. Some researchers have thought that apes have the capacity for language, but have never profited from a human like cultural milieu in which language was taught. They have just tried to teach apes, language system. Whether they have succeeded , and whether human children are really “taught” language...