click here.METHODS
Demographic Criteria Assessment
The analysis utilizes traditional approaches for the assessment of the
general physical characteristics of the age at death, sex, and stature of the
individuals in the sample (e.g. Stewart 1979; Brothwell
1981; Bass 1987; Isçan and Kennedy 1989). It consists of a five phase procedure, as
follows: 1) a general description and confirmation of the human origins of the
material; 2) the estimation and segregation of the minimum number of individuals;
3) the determination of sex; 4) the estimation of age, and; 5) the estimation
of stature.
General Description of the Skeletal Material
The human remains were separated from non-human remains, and the
individual bones and bone fragments were identified and classified. Observations were made on their condition and
preservation, and any evidence of post mortem damage to the material was
noted.
Minimum Number of Individuals
During this phase, the minimum number of individuals (MNI) was
estimated, and the skeletal material was separated into discrete
individuals. An a priori
assumption for the determination of the MNI is that an individual's remains
will not be spread out over more than one room.
This assumption was fundamental in determining and maintaining
chronological control during the initial excavations, and is followed in this
research. Determination of discrete
individuals was based on diagnostic bones indicative of at least one
individual. These include, for example,
the sternum, sided limb bones, and crania.
Determination of Sex
Observations regarding the sex distribution of the sample were compared
with metrical and morphological standards developed to delineate the sex of an
individual within a broader dimorphic distribution. Determination of sex is based on direct
observation of sexually dimorphic criteria.
Adult males and females differ in both general size and shape, and this
variation is reflected in the skeletal anatomy.
The determination of the sex of subadult
skeletons is more problematic than those of adults. However, the use of an inclusive approach
combining morphological and metrical characters has been tested with known
(sexed) series of modern skeletal material, and Jackes
(1992:195) has reported an accuracy rate of 85-95 percent.
Morphologically dimorphic features include such characteristics as the
shape of the pelvic girdle and the crania (Buikstra
and Ubelaker 1994:16). The pelvic girdle is the most sexually
dimorphic region of the skeleton, and it can be used to determine sex with a high
degree of accuracy (Bass 1987). The
sexual dimorphism of the pelvis is primarily the result of reproductive
mechanics, and is not readily apparent until adolescence. Beginning in adolescence, the female pelvis
expands relative to its height, while the male pelvis continues along
trajectories established at birth (Buikstra and Ubelaker 1994:16).
Holcomb and
Adolescent characters can begin to develop as early as nine years of
age. Detection of female aspects in a very young os coxae would indicate a high probability of accuracy
(Coleman 1969). Conversely, male
patterns observed in an adolescent os
coxae are to be considered inconclusive, as the
remains may represent a female as yet undeveloped (Buikstra
and Ubelaker 1994:16). In such cases, additional corroborative
evidence must be sought to make a firm determination of sex. In addition, male crania may retain a gracile, female form during early adolescence. Hence, detection of male characters in
adolescent skeletal material is suggestive of its masculinity (Buikstra and Ubelaker 1994:16).
Other metrically dimorphic attributes include the maximum diameter of
the femur head and the maximum facial breadth (Buikstra
and Ubelaker 1994:16). This form of variation is often continuous in
nature, with males being longer or larger than females. Discriminant
function formulae are used to segregate individuals based upon patterns of
sexually dimorphic growth and musculature (e.g., Snow et al.
1978; Stewart 1979; Richman et al. 1979; Kelley 1979; Steele 1980). The formulae are typically applied with the
most success to the long bones. Muscular
development is also sometimes evaluated through these formulae, but accurate
measurement of such development is problematic (Workshop of European
Anthropologists 1980; Brothwell 1981; Isçan and Miller-Shaivitz 1984; St.Hoyme and Isçan 1989).
An abbreviated listing of the metrical and morphological characters
utilized in sexing the skeletal material is presented in Table 2. A complete list of all characters recorded
and the organization of analytic methods is presented in Appendix A (Stewart 1979; Brothwell 1981; Isçan and Loth 1986; Isçan and Miller-Shaivitz 1986;
Bass 1987; Bennett 1988; Ubelaker 1989).
Estimation of Age at Death
The determination of age relies on the assessment of the physiological
age of the skeleton, as opposed to the chronological age of the
individual. The physiological age is
based upon relative growth patterns, and is hoped to give an accurate estimate
of chronological age, but environmental, nutritional, and disease stresses
often cause changes in the skeleton which will mask the true age of the
individual. In addition, the accuracy with
which age can be estimated varies inversely with the age of the individual at
death. In younger years, with age being
estimated primarily upon observed developmental changes, more precise estimates
are possible, whereas in older individuals, age estimates are more often
accomplished via the observation of degenerative changes, which offer less
accuracy.
Age determination can be accomplished through many means, and a holistic
analysis of all possible age‑related attributes is best for an overall
estimate. Some of the more typically
utilized attributes
include:
1. Dental Eruption and Occlusion
2. Cortical Bone Histology
3. Cranial Suture Closures
4. Postcranial Epiphyseal Unions
5. Pubic Symphyseal
Face Morphology
6. Age‑Related Degenerative
Conditions
7. Phase Changes in the Sternal Rib
8. Potpourri
1. Dental Eruption and Occlusion
Age estimates are based on the age of eruption of the deciduous and
permanent dentition. This method is
useful in age estimates of up to about 15 years. The third molar (wisdom tooth) erupts after
this time, but is so variable in age of eruption, if it erupts at all, that it
is not a very reliable age indicator.
See Bass pp. 289‑290 for an illustration of Ubelaker's
eruptive phases, noting the standard deviations. Occlusal wear has
also been offered as an indicator of age, but this has been shown to be highly
inaccurate, especially in archaeological context, where high‑grit content
diets (such as from the use of natural stone mano and
metate) can wear down the occlusal
surface of the tooth by the end of puberty ‑ see Bass pp. 286‑87,
after Brothwell (1965).
2. Cortical Bone Histology
Kerley (1984) developed a system of aging based on osteon
counts taken from midshaft long bone sections. This process involves counting the number of
whole osteons and osteon
fragments (which increase in number with age), and nonhaversion
canals and the percentage of circumferential lamellar bone in the cortex (which
decreases with age, completely disappearing around age fifty). These estimates are taken from the outer one
third on the cortex, with a normal light microscope in four fields at
100X. A percentage estimate is
calculated, and what is sought after is the rate of osteon
turnover or replacement. These
percentages are plugged into either a regression formula or a pre‑calculated
age\profile chart. Kerley
has obtained a reliability of almost 90% with a standard deviation of +/‑
5 years, with the best correlation coming from the fibula, then the femur and
tibia.
3. Cranial Suture Closures
This method bases age upon the degree of closure, union or ossification
of the cranial sutures. These methods
have until recently been considered inaccurate, but Meindel
and Lovejoy (1985) have introduced new evidence to indicate parietal ectocranial sutures are reliable indicators of age over 40
years. In addition, Mann et al. (1987)
have offered the four maxillary sutures and their rates of closure as reliable
age estimators ‑ see Bass pp.47‑48.
4. Postcranial Epiphysial Unions
(see handout #1) Endochondral
bones of the postcranium form via the union and
ossification of cartilaginous bridges between growing bones. This process can be seen to occur along a
growth algorithm, and can be used to estimate age at death. Handout #1, as well as Bass (1987), lists
some of these locations of epiphyseal union, as well as the approximate age
ranges for which these unions occur.
This data can be used on a union/non‑union basis, and McKern and Stewart have define five grades of epiphyseal
union: unobservable (0), beginning (1), active (2), recent (3), and complete
(4), and these offer a possibly more accurate estimate of age.
5. Pubic Symphyseal Face Morphology
(see handout #2) The pubic symphyseal
face in the young is characterized by an undulating surface, such as the crennulated surface of a typical non‑fused epiphyseal
plate. This surface undergoes a regular
progressive metamorphosis from age 18 onwards.
The phase system diagrammed in the handout, was
developed by Suchey and Brooks for the male pubic symphysis.
6. Age‑Related Degenerative Changes in Skeletal Features
Many non‑pathogenic conditions such as certain expressions of
arthritis and osteoporosis become more prevalent and pronounced in old age, and
can be used to give corroborative evidence in the determination of age. These occurrences are not entirely reliable
in themselves, however, as injury and pathological expressions of these
conditions can mimic the degenerative condition. An illustrative case can be seen in the osteophytic growths of the vertebral body (via
osteoarthritis). These growths form on
the outer margins of the centra, and Steward (1958)
has computed an age progression histogram for humans over 21 years based on the
percentage of extra‑central lipping as a
function of age for the lumbar and thoracic vertebra ‑ see Bass pp. 20‑21.
7. Phase Changes in the Sternal Ribs
Iscan and Loth have developed a system of age
estimation based on sequential changes at the sternal
end of the fourth rib. These changes are
similar to those that occur on the pubic symphyseal
face. They are of a specific
morphological nature and occur on the costochondral
joint between the rib and sternum. They
consider that these phases are not as subject to variation due to sex,
pregnancy and activity patterns as is the pubic symphyseal
face. See Bass (pp. 135‑142) for
photos of Iscan and Loth's
phases, with the general progression illustrated as an increase in the depth of
the articular depression and the degenerative
fragmentation, thinning and increased porosity at the edges of the articular surface over time.
8. Potpourri:
a. Note that generally females are more advanced than males with regard
to physiological age, being about two years advanced at puberty, five years at
maturity, and seven to ten years in old age.
b. The sacroiliac joint undergoes changes in morphology similar to those
at the pubic symphysis, Lovejoy et al. (1985) offers
a phase system based on these morphological changes.
c. Krogman (1949) offers a system of aging
based on transillumination through the scapular body
to chart the occurrence and amount of atrophic (thinning) centers, basically,
the more that are present, the older the individual.
d. Various radiographic analysis techniques focus on age related changes
to interior bone structures, such as at the costo‑chondral
juncture, the metaphyseal plates of the long bones,
and Walker & Lovejoy's (1985) radiographic analysis of trabecular
bone involution in the clavicle.
e. Bass (1987) and Ubelaker (1989) offer age
estimates based on long bone lengths, but these have a wide range of variation
even within a single relatively homogenous population.
Estimation of Stature
Estimation of stature is based on extrapolation formulae derived from populational averages of long bone lengths. These averages are computed from known
populations, resulting in some degree of error when applied to a sample from a
prehistoric population. The formulae
utilized are based on long bone lengths and corresponding statures derived from
data from historic Native American populations (Steele and McKern
n.d.; Steele 1980).
Bones utilized in this phase of analysis include the humerus, radius,
ulna, femur, tibia, and fibula.
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