Carstairs-McCarthy's book sets out a bold proposal that constitutes an exciting challenge to the idea that the development of modern syntax was driven by the contentful divisions of language. Instead he posits a physiological cause in order to explain why the core aspects of modern syntax are as they are. It is a great virtue of the book that it carefully reviews a vast interdisciplinary literature encompassing biology, anthropology, neuroscience and the study of apes to support this startling hypothesis. Moreover, the author does a good job of raising doubts about the handful of views that would otherwise contradict it. I conclude the review by arguing that the hypothesis has merits beyond its ability to provide potential answers to the main puzzles raised in the book. Specifically, it fits well with a rejection of a purely communicative model of language, according to which it functions simply to provide a public code for the expression of pre-existent conceptually based: thoughts. In this respect, it is in line with cutting edge work in cognitive science, concerning the relation of connectionist models and nonconceptual content, which suggests that cognitive processes are not initially structured after the fashion of language. However, I end by sounding a note of caution about some of the author's wider philosophical conclusions.