Biology Reference
In-Depth Information
Morphoscopic traits are used to assess the ancestry of a single individual for the purpose
of identification. The morphoscopic traits more commonly employed to assess ancestry can
be found in
Hefner (2009)
. These traits are drawn predominantly from trait lists found in
Rhine (1990)
and most introductory forensic anthropology textbooks. For an in-depth discus-
sion on historical aspects of morphoscopic trait analysis not covered herein, see Hefner and
colleagues' (2012) discussion of morphoscopic traits and the assessment of ancestry.
When assessing ancestry from an unknown set of skeletal remains we caution against the
use of typological trait lists that supposedly typify the skull of an individual derived from
a specific ancestral group, sensu
Rhine (1990)
. A more methodologically sound approach
involves focusing on individual traits (characters) and the variable expression of those traits
(character states) within and between populations. Remember, no single trait is found exclu-
sively in only one population, as with other phenotypic traits. As one of the authors has
demonstrated elsewhere (
Hefner et al., 2012
), shovel-shaped incisors are often cited as an
Asian-specific trait. While shoveling occurs in 70
e
85% of Asians worldwide (Scott and
Turner, 1997) (not 100% as may be believed), the same trait is also found in almost all other
populations, though in much lower frequencies (3
e
10% of Europeans; 8
e
11% of Africans
[Scott and Turner, 1997]).
Nonmetric traits are not discrete or isolated within one population due to multiple factors.
In fact, the variation results from very specific evolutionary mechanisms. Mechanisms such
as the genetic effects of selective pressures from particular environments, the effects of gene
flow between groups, and the random effects of drift and founding (
Lahr, 1996
) all play a role
in the expression of variation within and between groups. Of course, by definition the
different levels of gene flow, selection, and drift acting to establish this variation between
groups is closely linked to geography (
Lahr, 1996
), and it is this geographic division that
accounts for the high degree of variation observed among humans today.
Therefore, we need to understand the frequency of state expressions and meaningfully
combine them into suites of significant traits using appropriate statistical methods. In that
way we (anthropologists) can begin to see the necessary patterns of variation that permit
valid assessments of ancestry using morphoscopic data. As with the craniometric data
described earlier, this requires adequate reference data, standardized protocols for scoring
the variables, and appropriate statistics for categorical data analysis.
To that end, Hefner (2003, 2007, 2009) collected data on the expression of a large number
of morphoscopic traits from multiple skeletal populations and provided a series of simple,
direct illustrations of each character state. The complete list of traits (characters and char-
acter states) and populations are fully described elsewhere (
Hefner, 2009
). By collecting
such data, Hefner documented intergroup variation without making assumptions about
so-called racial groups, and developed empirically supported methods for assessing
ancestry.
How can these variables be combined to assess ancestry? The answer is via classification
statistics appropriate for categorical data. A number of statistical approaches have proven
useful to analyze morphoscopic data. Two of these are summarized below, and others
(k-nearest neighbor, canonical analysis of principal coordinates, and discriminant function analysis)
are discussed in
Hefner et al. (2012)
and
Hefner (2013)
. Two additional methods are outlined
below to give the reader a sense of the many ways this type of data can be used during
forensic anthropological analysis.
