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/
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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