Biology Reference
In-Depth Information
Population Structure and History
Geometric morphometric analyses have been applied to studies of biological distance,
population structure, and history. Early applications of geometric morphometrics to biolog-
ical distance analyses include McKeown (2000) and
McKeown and Jantz (2005)
. The use of
geometric morphometrics has been extended to larger, more geographically diverse samples
and has also been applied to questions regarding the interplay of genetics and environment
on the phenotype.
Building on previous geometric morphometric research into the peopling of the Americas
(
Perez et al., 2007; Gonzalez-Jose et al., 2008
),
Perez et al. (2009)
tested the discrepancy between
morphological variation and genetic data in explaining the number of founding populations
into the Americas. The degree of biological diversity during the Holocene (which began about
12,000 years ago) as shown in craniofacial morphology among populations in North and
South America has resulted in the proposal of two hypotheses regarding the peopling of
the Americas. One states there were multiple migrations and the second proposes a single
migration with local diversification. The two competing hypotheses are based on whether
one is using craniometric data (multiple migrations) or genetic data (local diversification).
To test these hypotheses,
Perez et al. (2009)
sampled Holocene remains from Central
Argentina and compared morphological and ancient genetic data. The authors used both
two-dimensional landmarks and semilandmarks digitized in the Frankfurt plane from
photographs taken on the facial and vault regions of the skull. mtDNA
haplogroup
data
were obtained from previous studies using the same Holocene remains from Argentina.
They found a lack of concordance between the molecular data and craniofacial morphology,
similar to a previous study (
Perez et al., 2007
). Their results demonstrated that even for the
early Holocene samples that show a distinct morphology from modern Native Americans,
the mtDNA haplogroups are the same. These findings might imply a single migration
from Northeast Asia or southern Siberia as detected in a recent study using whole-genome
sequencing (
Dulik et al., 2012
). If the rapid peopling of the continent occurred coupled
with extreme ecological diversity, a scenario of localized diversification is probable.
Smith et al. (2007)
investigated variation in the temporal bone and the relative contributions
of genetics and environment. Coordinates from 22 landmarks observed on temporal bones
from 11 modern population samples were registered with GPA. PC scores based on the GPA
output were used to assess variation across the groups sampled as well as to test for concor-
dance among group distances based on the coordinate and genetic data. Differences in the
shape of the temporal bone were found across all groups and discriminant analysis was able
to correctly classify individual specimens with a relatively high degree of accuracy. The
distance matrices based on coordinate and genetic data for the OldWorld samples were signif-
icantly correlated; however, this did not hold true when Native Americans were included in
the matrix correlation analyses. While temporal bone size did show strong correlation with
climate (temperature and latitude) suggestive of selective forces, shape was correlated with
geography and conformed to a model of isolation by distance. This research indicates that
temporal bone shape is selectively neutral and useful for distinguishing among groups.
In a follow-up to a previous study,
Smith (2009)
used coordinate data from 83 landmarks
collected on skulls from 14 modern populations. The dataset was broken into seven subsets
representing anatomical units, including the entire cranium, that were employed to calculate
