Biology Reference
In-Depth Information
In order to test the hypothesis that within extreme environments (cold, dry, hot, humid)
nasal cavities will exhibit features that enhance turbulence and air-wall contact to improve
conditioning of the air,
Noback et al. (2011)
sampled 10 modern human populations residing
in extreme climates and analyzed the shape of the bony nasal cavity using 21 landmarks. This
study demonstrated a high degree of correlation between nasal cavity morphology and
climatic variables. The authors concluded that nasal cavity morphology appears mostly
related to temperature, whereas morphology of the nasopharynx is associated with humidity.
Similar to previous studies, they found that the shape of the nasal aperture is higher and nar-
rower in cold climates compared to hot
e
humid climates. These shape changes in cold
e
dry
climates appear to be functionally consistent with an increase in contact with air and mucosal
tissue through greater turbulence during respiration and a higher surface-to-volume ratio in
the upper nasal cavity.
Growth and Development
Several studies have used geometric morphometrics to detect ontogenetic scaling and allo-
metric trajectories in human growth and development. As morphological variation develops
during growth, the study of ontogenetic series could identify forces (genetic or environ-
mental) responsible for the size and shape differences observed among adult crania.
Strand Viðarsd´ ttir et al. (2002) explored the ontogenetic basis for craniofacial variation in
10 groups of modern humans ranging in age from infancy to adulthood. GPA was per-
formed on coordinates from 21 landmarks. PCA was used to assess shape differences and
discriminant analysis was used to classify individual crania. Results indicate that human
facial form from birth contains population-specific morphologies. These distinct trajectories
lead to further developmental differences later in ontogeny and carry over to adult
morphology.
In another growth and development study,
Gonzalez et al. (2010)
analyzed the ontogeny of
facial robustness among prehistoric South American groups. Similar to Strand Viðarsd
´
ttir
et al. (2002), these authors found the pattern of interpopulation variation in shape and size
of facial form is established by the age of five, indicating that processes acting on facial
morphology during ontogeny contribute to the observed differences seen in adult variation.
Whether the observed developmental differences for robusticity are the result of random
changes, or more localized, adaptive processes, the authors could not conclude. This is an
area for further research.
Secular Change
Significant trends have occurred during the last 200 years in a number of human popu-
lations, including the U.S., Europe, and Japan. Significant attention has been paid to secular
changes in craniofacial morphology. These changes include increased cranial vault height
and changes in cranial vault width and have been seen in numerous populations, including
Euro-American and African American populations, and in both males and females. Wescott
and Jantz (2005) calculated two-dimensional coordinate data for 13 landmarks from cranio-
metric data and use the data to investigate secular trends in nineteenth and twentieth
century Euro-American and African American cranial morphology.
Individuals with
