Biology Reference
In-Depth Information
Cabana and colleagues (Chapter 16), this volume, for a discussion on what DNA analysis has
revealed about human variation. Biological distance can be defined as how closely related or,
alternatively, divergent populations are from one another. Given that one of the assumptions
with biodistance analysis is that changes in allele frequencies due to evolutionary forces such
as genetic drift and gene flow affect changes in phenotypic traits, including skeletal features
(
Stojanowski and Schillaci, 2006
), studies of biological distance are relevant for the ancestry
problem. Several workers have addressed the problem of human variation (especially within
bioarchaeological studies) using biological distance models, with perhaps the work of Rele-
thford and Blangero, and Konigsberg and colleagues being the most central (e.g.,
Relethford
and Lees, 1982; Relethford and Blangero, 1990; Relethford, 1991; Konigsberg, 1990, 2000;
Konigsberg et al., 1993; Konigsberg and Ousley, 1995
). Refer to
Konigsberg (2006)
for a review
and see McKeown and Schmidt (Chapter 12), this volume for more information on
biodistance.
ANCESTRY AND FORENSIC ANTHROPOLOGY
Ancestry is the third component of the biological profile, after age-at-death and sex esti-
mations. In any society with a diverse population like the United States, part of the recovery
of decomposed, damaged, and/or skeletonized human remains from a medicolegal purview
(e.g., from clandestine disposal to mass disaster) will often include questions by law enforce-
ment regarding the race, or ancestry, of the victim.
When the skull (and more importantly the facial skeleton) is complete, the likelihood of
estimating ancestry accurately is assumed to be high. We state this with a caveat however,
as correct ancestry estimation depends on (1) the availability of an appropriate reference
sample (discussed below), and (2) the analyst's ability and experience with the measurement
techniques and his or her ability to correctly understand and visually assess the cranial
nonmetric features associated with various ancestral groups.
However, as Sauer (1992:107) questioned, “If races don't exist, why are forensic anthropol-
ogists so good at identifying them?” The answer to this question lies in the fact that concor-
dance exists between social race categories (i.e., Black, White) and cranial morphology
(
Ousley et al., 2009
). Evolutionary forces (e.g., gene flow, genetic drift) have led to a discor-
dance of skeletal traits (and other phenotypic traits) between populations enabling us to
measure and analyze that data. This leads to ancestry estimations based on our knowledge
of trait frequency in each major population group
e
e.g., variation in cranial morphology
is structured by geography (
Kennedy, 1995; Relethford, 2009
).
Sauer (1992)
and Konigsberg
et al. (2009) further reason that we must use the same terminology for ancestry categories
used by the medicolegal community in order to make a contribution to the identification
of remains.
There are two generally accepted methods of ancestry estimation in forensic anthropology:
(1) metric analysis of cranial and postcranial measurements, and (2) nonmetric (morpho-
scopic) traits of the cranium. There are advantages and disadvantages to each of these
approaches (outlined below). Prior to an in-depth look at each, a general comparison of
the statistical treatment for each is warranted.
