How and where does the rich diversity of languages in the world come from?

There are over 6500 spoken languages in the world. And even this figure could well be an underestimation of reality, as there are some languages that are not recorded at all and some that have died (languages die when there are no more speakers speaking that language). Also, one language can have many dialects, some of which can become mutually unintelligible over time.

Languages that look similar in morphology, phonology and syntax seem to belong to the same language family. Some theories claim that all the languages that you see in the world have actually originated from one single language (the protolanguage). There is a mention of such a “pure language” in religious texts like Bible also.

Once humans had this first language, it is easier to explain how the rich diversity of languages that we see around came to existence. For instance, new languages (pidgins and creoles) are formed through language contact situations. Even existing languages change rapidly with time (synchronically and diachronically), giving rise to different dialects. If and when speakers of these dialects are separated due to geographical or other constrains, these dialects become distinct languages over time.

But it is nearly impossible to explain when and how did this first language originate? A more important question is why were only humans gifted with language faculty?

Language is species specific to humans. Other animals also have some modes of communication (bee dancing, bird songs, etc.), but none of the communication channels recorded so far are even close to human language. Charles Hockett gave a list of 16 design features that make human language unique. Amongst other things, our language gives us the power to talk about language (see the reflexiveness design feature). Note that when I refer to language, I do not mean a particular language like English, French or Hindi. I mean “language faculty.” A human child is born with the capacity (read Noam Chomsky’s Universal Grammar) to learn any language of the world if he or she is exposed to it at the right age (read "critical age hypothesis"). In fact, one can say that language alone is responsible for making Homo sapiens- sapiens so unique and different from the rest of the animal kingdom.

The branch of linguistics that deals with the origin and evolution of language and language faculty is known as Evolutionary Linguistics. Evolutionary linguistics relies heavily on data from other fields like evolutionary biology, archaeology, neurology, comparative anatomy, anthropology, genetics, cognitive sciences, etc. Different linguists have proposed theories on the evolution of language. The discontinuity theory, for instance, talks about a random mutation in the human genome at some point in the history that suddenly resulted in language faculty. The continuity theory talks about some primitive, pre-linguistic structures that gradually gave rise to the complex linguistic structures we have today. Some theories attribute language faculty as a byproduct of some other developmental change in the human anatomy or morphology.

There are many problems to studying language history and evolution. Language is absent in our closest kin (apes, chimpanzees, etc.), and in our immediate ancestors, Homo sapiens neanderthalensis. Hence, comparative studies do not give desirable results. Besides this, the lack of the possibility of fossil records for spoken language complicates the studies on language evolution.