The anatomic basis for the acquisition of speech and obstructive
sleep apnea: Evidence from cephalometric analysis supports
The Great Leap Forward Hypothesis
Terence M. Davidson
, Jacob Sedgh
, Duyen Tran
, Carl J. Stepnowsky Jr.
Department of Otolaryngology—Head and Neck Surgery, University of California, San Diego, CA, USA
Surgery Service, VA San Diego Health Care System, San Diego, CA, USA
Department of Psychiatry, University of California, San Diego, CA, USA
Health Services Research and Development Service, VA San Diego Health Care System, San Diego, CA, USA
Received 25 August 2004; received in revised form 21 February 2005; accepted 4 March 2005
Available online 1 July 2005
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
. 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.
q 2005 Elsevier B.V. All rights reserved.
Keywords: Obstructive sleep apnea; Apnea–hypopnea index; Klinorynchy; Laryngeal descent; Craniobase angulation; Supralaryngeal vocal cord tract;
Jeffrey T. Laitman et al. write,
The acquisition and processing of oxygen and its byproducts
is the primary mission of any air-breathing vertebrate.
Chewing, walking, reproducing, thinking are all ﬁne, but
ﬁrst one has to breathe. Anthropologists sometimes seem to
forget this; evolution never does .
Theodosius Dobzhansky said, “Nothing in biology makes
sense except in the light of evolution.”
Forty thousand years ago, a critical change in the
evolution of Homo sapiens, termed ‘The Great Leap
Forward’, resulted in the ﬁnal component of today’s high-
tech civilization. Jared Diamond postulated that the cause for
the Great Leap was the ‘anatomic basis for spoken complex
language’.  In 1999, Laurence Barsh wrote an article, titled
‘The Origin of Pharyngeal Obstruction During Sleep’, in
which he described several anatomic changes seen in recent
evolution, which contributed to pharyngeal collapse during
Sleep Medicine 6 (2005) 497–505
1389-9457/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
Corresponding author. Address: University of California, San Diego,
9500 Gilman Drive 0617, La Jolla, CA 92093-0617, USA. Tel.: C1 858
822 4229; fax: C1 858 822 5908.
E-mail address: firstname.lastname@example.org (T.M. Davidson).