How can a multimodal approach to primate communication help us understand the evolution of communication?

From the book : Evolutionary Psychology 11 issue 3 : 538-549.
Scientists studying the communication of non-human animals are often aiming to better understand the evolution of human communication, including human language.
Some scientists take a phylogenetic perspective, where the goal is to trace the evolutionary history of communicative traits, while others take a functional perspective, where the goal is to understand the selection pressures underpinning specific traits.
Both perspectives are necessary to fully understand the evolution of communication, but it is important to understand how the two perspectives differ and what they can and cannot tell us.
Here, we suggest that integrating phylogenetic and functional questions can be fruitful in better understanding the evolution of communication.
We also suggest that adopting a multimodal approach to communication might help to integrate phylogenetic and functional questions, and provide an interesting avenue for research into language evolution.