Voice Modulation: A Window into the Origins of Human Vocal Control?

An unresolved issue in comparative approaches to speech evolution is the apparent absence of an intermediate vocal communication system between human speech and the less flexible vocal repertoires of other primates. We argue that humans' ability to modulate nonverbal vocal features evolutionarily linked to expression of body size and sex (fundamental and formant frequencies) provides a largely overlooked window into the nature of this intermediate system. Recent behavioral and neural evidence indicates that humans' vocal control abilities, commonly assumed to subserve speech, extend to these nonverbal dimensions. This capacity appears in continuity with context-dependent frequency modulations recently identified in other mammals, including primates, and may represent a living relic of early vocal control abilities that led to articulated human speech.