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Tuesday, March 29, 2016

Nasal cavities

http://www.eurekalert.org/pub_releases/2016-03/p-hae031616.php 
Human ancestors explored 'out of Africa' despite impaired nasal faculties 

In humans inhaled air is conditioned poorly in the nasal cavity in 
comparison with primates, such as chimpanzees and macaques, according 
a recent study published in PLOS Computational Biology. Unlike our 
protruding external nose, which has little effect on improving air 
conditioning performance, other hominins (including 
australopithecines) were endowed with flat nasal features and 
faculties to improve air conditioning. 

The study, produced by Dr Takeshi Nishimura from Kyoto University and 
colleagues, is the first investigation of nasal air conditioning in 
nonhuman hominoids based on computational fluid dynamics (CFD). 

The human nasal passage conditions inhaled air in terms of temperature 
and humidity to match the conditions required in the lung. 
Insufficient conditioning can damage the tissues in the respiratory 
system and impair respiratory performance, thereby undermining health 
and increasing the likelihood of death. 

Our ancestors, the genus Homo, diversified under the fluctuating 
climate of the Plio-Pleistocene, to be flat-faced with a short nasal 
cavity and a protruding external nose, as seen in modern humans. 
Anatomical variation in nasal region is believed to be evolutionarily 
sensitive to the ambient atmospheric conditions of a given habitat, but 
the nasal anatomy of early Homo was not sensitive to the ambient 
atmosphere conditions. The inhaled air can be fully conditioned 
subsequently in the pharyngeal cavity, which was lengthened in early 
Homo. 

... These linked changes in the nasal and pharyngeal regions would in 
part have contributed to how flat-faced Homo members must have survived 
fluctuations in climate, before they moved "Out of Africa" in the Early 
Pleistocene to explore the more severe climates and ecological 
environments of Eurasia. 



http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1004807 
Impaired Air Conditioning within the Nasal Cavity in Flat-Faced Homo 

Abstract 

We are flat-faced hominins with an external nose that protrudes from 
the face. This feature was derived in the genus Homo, along with facial 
flattening and reorientation to form a high nasal cavity. The nasal 
passage conditions the inhaled air in terms of temperature and humidity 
to match the conditions required in the lung, and its anatomical 
variation is believed to be evolutionarily sensitive to the ambient 
atmospheric conditions of a given habitat. In this study, we used 
computational fluid dynamics (CFD) with three-dimensional topology models 
of the nasal passage under the same simulation conditions, to investigate 
air-conditioning performance in humans, chimpanzees, and macaques. The 
CFD simulation showed a horizontal straight flow of inhaled air in 
chimpanzees and macaques, contrasting with the upward and curved flow in 
humans. The inhaled air is conditioned poorly in humans compared with 
nonhuman primates. Virtual modifications to the human external nose 
topology, in which the nasal vestibule and valve are modified to resemble 
those of chimpanzees, change the airflow to be horizontal, but have 
little influence on the air-conditioning performance in humans. These 
findings suggest that morphological variation of the nasal passage 
topology was only weakly sensitive to the ambient atmosphere conditions; 
rather, the high nasal cavity in humans was formed simply by evolutionary 
facial reorganization in the divergence of Homo from the other hominin 
lineages, impairing the air-conditioning performance. Even though the 
inhaled air is not adjusted well within the nasal cavity in humans, it 
can be fully conditioned subsequently in the pharyngeal cavity, which 
is lengthened in the flat-faced Homo. Thus, the air-conditioning faculty 
in the nasal passages was probably impaired in early Homo members, 
although they have survived successfully under the fluctuating climate 
of the Plio-Pleistocene, and then they moved “Out of Africa” to explore 
the more severe climates of Eurasia. 

Author Summary 

This is the first investigation of nasal air conditioning in nonhuman 
hominoids based on computational fluid dynamics with digital topological 
models of the nasal passage made using medical imaging. Our comparative 
results of humans, chimpanzees, and macaques show that the inhaled air 
is conditioned poorly in humans compared with nonhuman primates. We also 
show that our protruding external nose has little effect on improving 
air conditioning. The nasal anatomy in Homo was weakly sensitive to the 
ambient atmosphere conditions in evolution, but was formed passively by 
facial reorganization in this genus. Even though the inhaled air is not 
adjusted well within the nasal cavity in humans, it can be fully 
conditioned subsequently in the pharyngeal cavity, which is lengthened in 
flat-faced Homo. Thus, despite an impaired air-conditioning conformation 
in the nasal passages, Homo members must have survived successfully under 
the fluctuating climate of the Plio-Pleistocene, and then they moved “Out 
of Africa” in the Early Pleistocene to explore the more severe climates 
and ecological environments of Eurasia. 
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