The evolution of human speech: The role of enhanced breathing control

Abstract

Many cognitive and physical features must have undergone change for the evolution of fully modern human language. One neglected aspect is the evolution of increased breathing control. Evidence presented herein shows that modern humans and Neanderthals have an expanded thoracic vertebral canal compared with australopithecines and Homo ergaster, who had canals of the same relative size as extant nonhuman primates. Based on previously published analyses, these results demonstrate that there was an increase in thoracic innervation during human evolution. Possible explanations for this increase include postural control for bipedalism, increased difficulty of parturition, respiration for endurance running, an aquatic phase, and choking avoidance. These can all be ruled out, either because of their evolutionary timing, or because they are insufficiently demanding neurologically. The remaining possible functional cause is increased control of breathing for speech. The main muscles involved in the fine control of human speech breathing are the intercostals and a set of abdominal muscles which are all thoracically innervated. Modifications to quiet breathing are essential for modern human speech, enabling the production of long phrases on single expirations punctuated with quick inspirations at meaningful linguistic breaks. Other linguistically important features affected by variation in subglottal air pressure include emphasis of particular sound units, and control of pitch and intonation. Subtle, complex muscle movements, integrated with cognitive factors, are involved. The vocalizations of nonhuman primates involve markedly less respiratory control. Without sophisticated breath control, early hominids would only have been capable of short, unmodulated utterances, like those of extant nonhuman primates. Fine respiratory control, a necessary component for fully modern language, evolved sometime between 1.6 Mya and 100,000 ya.

The animal nature of spontaneous human laughter

“…Spontaneous emotional vocalizations have different underlying neural and physiological control pathways than the speech system, so an adaptive perceptual design should be sensitive to those acoustic features that best distinguish spontaneous laughs from those produced volitionally. MacLarnon and Hewitt (1999) described the recent evolution of increased thoracic innervation in humans that serves fine breathing control during speech production. One consequence of slowed breathing for speech is the reduced presence of inspiratory elements between voiced speech segments.…”

The biology and evolution of music: A comparative perspective

“…A recently discovered fossil indicator of a potential change in neural control of vocalization in humans is that modern humans have a larger thoracic vertebral canal than other primates (MacLarnon & Hewitt, 1999). Because the motor neurons in this region of the spinal cord control some respiratory muscles (intercostals and abdominals, but not the diaphragm as often stated) this enlargement may be linked to greater control over breathing.…”

Empirical approaches to the study of language evolution

“…Given that all mammalian species examined have a flexible capacity to lower the larynx during vocalization (Fitch, 2000a), and many species possess a descended larynx much more extreme than that in humans (Fitch & Reby, 2001;Weissengruber, Forstenpointner, Peters, Kübber-Heiss, & Fitch, 2002), it is clear that the much-discussed role of the descended larynx in human speech has been greatly overestimated in its importance (Fitch et al, 2016). This means that most attempts to estimate the onset of speech abilities based on fossils are dead ends (reviewed in Fitch, 2009a), with the possible exception of thoracic canal size, indicating an increase in breath control (MacLarnon & Hewitt, 1999). Like hearing, the anatomy of the primate vocal tract was essentially Bspeech ready^whenever the neural control and cognitive capabilities evolved, as concluded long ago by both Darwin and Negus (Darwin, 1871;Negus, 1938).…”