Biology Reference
In-Depth Information
average 55%. That is, shape and size components of craniofacial traits are moderately heri-
table from generation to generation. This approach has been successfully applied to
numerous studies employing craniometric data; perhaps the most notable are studies by
Relethford (1994, 2001, 2002, 2004, 2009, 2010)
demonstrating that patterns of within- and
between-group variation based on craniofacial morphology are congruent with genetic
studies. The Relethford
e
Blangero model, as it is now known, has now been successfully
applied to numerous studies in skeletal biology for identifying population structure and
inferring population histories in evolutionary terms.
The 1990s also saw an explosion in the growth of forensic anthropology and an increasing
need for reliable methods for assessing biological characteristics for unknown individuals.
Social race
can be an important identifier for searching missing persons reports and methods
for estimating genetic ancestry (which can approximate social race) were clearly needed.
Jantz and Ousley (1996
e
2005) developed the program FORDISC for use with craniometrics
and postcranial metrics. The program generates custom discriminant functions for classi-
fying unknown individuals based on comparison with a series of reference samples. It also
provides plots of canonical scores so that the distance between the unknown and any
comparison group centroid can be visually evaluated. While the program is user friendly,
it still requires understanding of the basic statistical procedures and underlying assumptions
associated with DFA and CVA to properly interpret results. The use of craniometrics for clas-
sifying unknown individuals has demonstrated a fairly high rate of accuracy (
Ousley et al.,
2009
). For more information on this topic and approach, see DiGangi and Hefner (Chapter 5),
this volume.
Traditional Morphometric Data
For the biological anthropologist, all measurements of skeletal elements fall under the
rubric of osteometrics. Measurements of the cranium and mandible are typically referred
to as craniometrics. Postcranial metrics include measurements of the rest of the skeleton.
Measurements of dental dimensions are odontometrics. The typical tool kit for observing
skeletal and dental dimensions includes spreading and sliding calipers, a radiometer, a coor-
dinate caliper, an osteometric board, and a measuring tape. The craniometric canon was
established by
Howells (1973)
.
Buikstra and Ubelaker (1994)
provide a list of recommended
cranial, postcranial, and dental measurements to standardize measurements of human
skeletal remains for the purposes of documentation and analysis. Definitions for these
measurements are provided in the aforementioned volumes. Anyone interested in morpho-
metric research should carefully read the definitions and practice observing the measure-
ments before proceeding with data collection. The measurements chosen and the accuracy
of observation can have a significant effect on the validity of the research results.
Raw linear distances contain both size and shape information. For example, males typi-
cally have larger crania than females and on average have a greater maximum cranial length
(glabella-occipital length). This difference is due to both the larger overall size of the male
cranium (on average) and shape differences in the glabellar and occipital regions between
the sexes. Thus, a major source of variation in samples composed of both males and females
is size related to sexual dimorphism. Therefore, without standardizing data transformations
such as Z-scores or applying a size correction such as scaling variables by the geometric
