When did our ancestors start speaking and why? Do all human languages originate from a unique "mother tongue" or from several different independent sources? Did the introduction of language precede the development of human rational thought or the other way round?

Unfortunately, historical linguistics cannot answer such questions by its own scientific tools. Comparative methods enable us to go back in time by grouping languages into families and reconstructing the common ancestor from which all the languages of the family derive. Moreover, families can be grouped into super-families by lighter (and more controversial) methods, but the accessible time-depths are still too short to address the issue of the origin of language anyway. Nevertheless, these studies play an important role in tracing back the history of early migrations of modern humans, when they are used in conjunction with population genetics and archaeology. Actually, combining linguistic and genetic findings is very valuable because they provide different and complementary pieces of information that can contribute to confirm or infirm hypotheses about first settlements in different parts of the world.

As for the origin of language, we must turn toward other linguistic fields, rather than historical linguistics. Following Derek Bickerton, many authors in the field think that language has been preceded by a rudimentary communication system called "protolanguage" and that the emergence of fully-fledged human language took place during the transition from Homo erectus and archaic Homo sapiens to our own species. If this is the case, it remains an open question to discover why our ancestors have needed this important improvement in their communication system. One of the most important methods is to look for hints by examining structural properties, specially in syntax and semantics, which are shared by all human tongues (universals of human language) and which are not shared by other communication systems (specificities of human language). Obviously, the chances are that such properties are related to fundamental functions of language that could account for its emergence.