Grammaticalization is most often studied in the larger context of language evolution. Though most who are interested in language agree that Darwinian evolution has a hand in the emergence of the phenomenon, there is no real consensus as to how this happened. There seems to be an intuitive notion that in whatever manner language happened, its development was a choice. It is not clear that this intuition can be well founded.
As we have seen, Hurford, postulates that the genetic evolution of humans has led to a LAD which is now heritable, imbedded in our genes. The concept of LAD implies that its function is to deal with grammaticalized language and is for communicating.
Michael C. Corbalis [16] is also one that believes in language as a human/hominid pursuit though not from a genetic standpoint. Corbalis believes that before humans used spoken language they used a form of gestural language. Corbalis emphasizes that spoken language is fairly recent in the history of humanity - only around 50 000 years old. He thinks that grammatical languages might have emerged before the event of spoken language - a form of American sign language - and that the capability for spoken language may have been possible long before it happened. Early humans may have adopted speech simply because it seemed like a good idea. This would make the event of speech a cultural invention much like writing, and not the result of structural changes in the brain.
Corbalis has based some of his ideas on the fact that 50 000 years ago there was an explosion of new technologies: new tools, drawings, textiles, musical instruments etc. In contrast, there was little evolution in artifact 2 000 000 years before that. Corballis hypothesizes that with the advent of spoken language, hands were now free to do other things.
However, there is another point of view: Language, as we know it, is the result of a lengthy process subject to evolutionary pressures of which language is a consequence and not the cause. That is, language is an incidental consequence of a series of events.
John Haiman [28] suggests that two fundamental principles, habituation and emancipation, are fundamental dynamics that can usefully describe the process of grammaticalization. Habituation and emancipation are concepts borrowed from psychology and ethology that describe ritualization of behavior through repetition. Habituation may have its roots in communicative behavior that become eroded in form and consequently in function; however, emancipation refers to non-communicative behaviors that become freed from their instrumental action to develop a semiotic or symbolic role.
William H. Calvin postulates that language is the incidental effect of the required fine tuning of motor functions for ballistic movements and not a consequence of an evolutionary process that led to a (LAD). Calvin proposes that motor functions and the processes of language are synaptically related. The requirements of ballistic movement are such that once a missile is launched the trajectory cannot be modified. Calvin believes that in order to target with any accuracy, early humans had to develop, in conjunction, the ability to fine-tune hand and arm motion and the ability to pre-process synaptically the consequences of their throwing action. This, Calvin believes, also promoted the specialization of particular motion controls in specific areas of the brain, that is, the superficial layers of the neocortex.