The evolution of communication provides one of the few examples in evolutionary biology where principles of physical acoustics, interacting with developmental constraints on physiology and motor control, have clear and predictable effects on evolutionary outcomes. I will provide two clear example of this, relating to basic physiological constraints on fundamental and formant frequencies, and various morphological "tricks" that vertebrates have evolved to evade such constraints. Then I will explore a more speculative hypothesis concerning the neural control of vocalization: that the production of complex learned vocalizations requires particular neural correlates (direct fronto-bulbar connections) and behaviours ("babbling" or subsong), and furthermore that constraints on development may mean that there are only a few ways to achieve such vocal capabilities, raising the interesting possibility of "deep homology" in the evolution of communication. This hypothesis, though speculative, is testable and is consistent with the most recent information on genes involved in vocal learning.