Scientists who study primate communication, with the goal of understanding human communication, pursue two different, yet related, questions. Some scientists ask phylogenetic evolutionary questions (what was the historical pathway of a specific communicative ability?), and others ask functional evolutionary questions (what were the selection pressures that led to evolutionary changes in this domain?). These two types of question are both necessary to fully understand the evolution of communication, and one is not necessarily more important or useful than the other. Interestingly, integration between these two foci is rare, despite the potential benefits of integration. Integration between phylogenetic and functional questions could be highly informative when considering the evolution of communication, as understanding the reasons for change could help elucidate the specific process of change, and vice versa. Here, we argue that one way to bridge the gap between phylogenetic and functional questions could be to adopt a more multimodal approach to the study of primate communication, which is usually neglected in favour of a unimodal approach.
In this final chapter, we first summarize the general advantages of adopting a multimodal approach (see Chapter 5), regardless of whether the research questions are phylogenetic or functional. Second, we discuss the difference between phylogenetic and functional questions. Finally, we propose that integration between phylogenetic and functional questions would be helpful to move the field forward, and that a multimodal approach could be particularly useful in this endeavour (see also Waller et al., 2013a).