Voluntary Control of Breathing
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In mammals, ventilation is controlled by the autonomic nervous system and gas exchange in the lungs is the primary control for respiratory rate. Humans are also able to voluntarily override automatic respiration, allowing breath holding and prolonged vocalizations. Interestingly, in humans with congenital central hypoventilation syndrome (nicknamed "Ondine's curse") autonomic respiratory control is lost due to malfunction of central control of respiration in the brainstem. The development homeobox gene, PHOX2B, is strongly associated with Ondine's curse and thus may be linked to voluntary control of breathing.
It has been suggested that chimpanzees are not capable of voluntary control of their breathing, although better studies are needed to accurately confirm this.
The largely dismissed aquatic ape theory suggests hominid ancestors spent a period of time in a water environment and developed diving skills which require refined control of breathing. The theory further posits the brain structures that voluntarily control of the airway anatomy and respiratory control could also be used for elaborating sound production and provide the basis for uniquely human speech.
Controlled breath-holding has been shown in multiple human studies to reduce cortisol and stress levels, potentially providing a selection bias on humans able to voluntarily control respiration.
The loss of laryngeal air sacs is also associated with the ability to modify breathing patterns and reduce need for an anti-hyperventilating anatomy.
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The evolution of human speech: the role of enhanced breathing control., , Am J Phys Anthropol, 1999 Jul, Volume 109, Issue 3, p.341-63, (1999)
Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis., , J Hum Evol, 1997 Oct, Volume 33, Issue 4, p.479-94, (1997)
Was Man More Aquatic in the Past?, , The New Scientist, p.642-645, (1960)