Human craniofacial evolution: A cause for obstructive sleep apnea

In 1859, Charles Darwin revealed his theory of evolution by natural selection in his famous book “On the Origin of Species.” According to the theory, natural selection is the process by which organisms evolve over time to allow for better adaption to its environment in order to survive and have more offspring [1]. In Homo sapiens (humans), the notion of natural selection is observed in the way we perform our activities of daily living. In 2003, Davidson et al. [2] presented data supporting the concept that craniofacial structural and anatomical changes took place for the development of speech and language (Figure 1). Unfortunately, the undesired consequence of this evolution facilitated obstructive sleep apnea (OSA) in modern humans [2].

Figure 1. (a) Pan Troglodyte. (b, c) Transition from Pan Troglodyte to Homo sapiens. (d) Homo sapiens (genus and species of man).

Klinorynchy is the posterior migration of the splanchnocranium (facial skeleton) under the neurocranium [2]. This shift shortens the maxilla, palate, ethmoids, and mandible in order to provide speech and language. These changes are seen in the evolution from Pan Troglodyte, a common chimpanzee, to the modern Homo sapien [2]. According to Crelin et al. [3], the anterior migration of the foramen magnum with pharyngeal collapse is part of the evolutionary change to facilitate speech but diminishes olfaction. Lieberman et al. [4] proposed that the change from an obtuse to an acute cranial base angulation seen in the modern Homo sapiens furthered the development of speech, resonance, and voice.

In regards to tongue position, Negus et al. [5] described that the posterior migration of the tongue into the pharynx decreased the oral cavity size to improve speech and deglutition. In the animal kingdom, the mechanism known as the epiglottic–soft palate lock-up, the overlapping of the epiglottis and soft palate, is prevalent [2]. Interestingly, the mechanism is present in infant Homo sapiens, but disappears as the soft palate shortens and the larynx descends, in order to promote buccal speech [2]. Although these adapted anatomical features facilitate speech and the development of language, they also predispose humans to OSA.

Although the central reason for these anatomical changes were to develop voice, speech, and language, it is also recognized that these advances contributed to development of binocular vision and bipedalism [2]. We hypothesize that a separate series of events could have occurred in the central nervous system, which led to speech and OSA. With the understanding of craniofacial evolution in humans, perhaps we can orthodontically or surgically modify the mandible, maxilla, palate, pharynx and/or tongue to maintain appropriate speech but reduce the severity of OSA.

Disclaimer

The views expressed in this manuscript are those of the author(s) and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the US Government.

Camilo Fernandez-Salvador, MD
Department of Otolaryngology, Head and Neck Surgery, Tripler Army Medical Center, HI 96859, USA
[email protected] A. Song, MD
Edward T. Chang, MD, MS
Macario Camacho, MD
Department of Otolaryngology, Head and Neck Surgery, Tripler Army Medical Center, HI 96859, USA