The capacity for speech clearly differentiates humans from other primates, indicating that some of these mechanisms have diverged, in recent human evolution, from those of our prelinguistic ancestors. Speech, as the preferred output modality for human language, is an unusual feature of our species that depends upon a complex but well-understood set of mechanisms, including vocal/motor, auditory/perceptual, and central neural mechanisms. Paleo-DNA from fossil hominins provides an exciting new opportunity to determine when these derived speech production mechanisms arose during evolution. In contrast, the central neural mechanisms underlying speech production involve crucial derived characteristics (direct monosynaptic connections from motor cortex to laryngeal motor neurons, derived intracortical dorsal circuitry between auditory and motor regions). Regarding speech production, human peripheral vocal anatomy includes several derived characteristics (permanently descended larynx, loss of air sacs), but their importance has been overestimated. There is little evidence for human-specific mechanisms in auditory perception, and the hypothesis that speech perception is “special” is poorly supported by comparative data. Understanding when and why these evolved is central to understanding the evolution of speech. By first identifying mechanisms that are evolutionarily derived relative to other primates, we obtain members of the faculty of language, derived components (FLD). I analyze the biological underpinnings of human speech from a comparative perspective.
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