Category one and two combine when considering that the "universal characteristics of language may be so because they are aspects that make it more easily acquirable."2
The evolutionary nature of language is a new category of investigation that attempts to determine what occurred in our ancestral lineage that gave rise to a form of communication that is distinct from other species. This category involves genetics, paleontology, and archaeology.
However, whereas these studies benefit from a rich fossil record, evolutionary linguistics suffers from a lack of evidence. To overcome these shortcomings, linguists often make use of studies in the four categories already discussed.
However, Kinsella's research is unique in that it will not rely on the four categories. Instead, she utilizes evidence from evolutionary studies that will shed a critical light on the theory of linguistics.
The essential argument Kinsella makes is that this research is a step in developing a more unified theory of linguistics. This is much like psycholinguistics or neurolinguistics before it, which incorporate diverse disciplines in founding new conclusions.
Kinsella frames the current discussion on language within syntactic theory. ...