The anatomic basis for the acquisition of speech and obstructive sleep apnea: evidence from cephalometric analysis supports The Great Leap Forward hypothesis.

Background and Purpose: We previously postulated how evolutionary changes in man's upper respiratory tract to facilitate speech, a phenomenon Jared Diamond calls The Great Leap Forward, have predisposed man to obstructive sleep apnea (OSA) [Diamond J. The Third Chimpanzee: the evolution and future of the human animal. New York: HarperCollins Publishers; 1992. p. 21, 23, 32-54, 54-6; Davidson TM. The Great Leap Forward: the anatomic evolution of obstructive sleep apnea. Sleep Medicine 2003;4:185-94]. We grouped these anatomic changes into four categories: klinorynchy, laryngeal descent, craniobase angulation and supralaryngeal vocal tract (SVT) ratio of SVT(H):SVT(V). This study was designed to investigate the relationship between cephalometric measures corresponding to these anatomic changes and OSA.
Patients and Methods: One hundred and twenty-three male subjects presenting with symptoms of OSA underwent unattended multi-channel home sleep studies. We obtained cephalometric measurements from standard lateral cephalograms. Pearson correlation coefficients were calculated between cephalometrics and apnea-hypopnea index (AHI), age, and body mass index (BMI).
Results: Our results showed significant correlation between AHI and klinorynchy, laryngeal descent, and craniobase angulation.
Conclusions: Overall, our data supports the theory that evolutionary anatomic changes to facilitate speech correlate with OSA severity. The cumulative changes in each cephalometric category trended in the directions hypothesized and support the Great Leap theory of OSA evolution.