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.

TrendsSource–filter theory is the unifying methodological framework in the study of nonverbal vocal communication in humans and other vertebrates.Numerous studies have implicated fundamental frequency (F0) and vocal tract resonances (formants) in mammalian social communication. In humans, these sexually dimorphic source and filter voice features reliably indicate sex, age, body size, and dominance.By focusing on static rather than dynamic vocal processes, this literature has largely overlooked the human capacity to volitionally modulate F0 and formants to express or exaggerate ecologically relevant traits, often in response to specific social contexts.Emerging research suggests that F0 and formant scaling is widespread in humans and present in some other mammals, potentially representing an evolutionary path from simple voice-frequency scaling to articulated human speech.