Connecting primate gesture to the evolutionary roots of language: A systematic review

Standardized systematic search strategies facilitate rigor in research. Current search tools focus on retrieval of quantitative research. In this article we address issues relating to using existing search strategy tools, most typically the PICO (Population, Intervention, Comparison, Outcome) formulation for defining key elements of a review question, when searching for qualitative and mixed methods research studies. An alternative search strategy tool for qualitative/mixed methods research is outlined: SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type). We used both the SPIDER and PICO search strategy tools with a qualitative research question. We have used the SPIDER tool to advance thinking beyond PICO in its suitable application to qualitative and mixed methods research. However, we have highlighted once more the need for improved indexing of qualitative articles in databases. To constitute a viable alternative to PICO, SPIDER needs to be refined and tested on a wider range of topics.

We argue that an understanding of the faculty of language requires substantial interdisciplinary cooperation. We suggest how current developments in linguistics can be profitably wedded to work in evolutionary biology, anthropology, psychology, and neuroscience. We submit that a distinction should be made between the faculty of language in the broad sense (FLB) and in the narrow sense (FLN). FLB includes a sensory-motor system, a conceptual-intentional system, and the computational mechanisms for recursion, providing the capacity to generate an infinite range of expressions from a finite set of elements. We hypothesize that FLN only includes recursion and is the only uniquely human component of the faculty of language. We further argue that FLN may have evolved for reasons other than language, hence comparative studies might look for evidence of such computations outside of the domain of communication (for example, number, navigation, and social relations).