Biology Reference
In-Depth Information
morphological sex estimation on juveniles is “tentative at best.”
Komar and Buikstra (2009)
caution that there are no reliable methods for sex estimation for subadults. There are two
major obstacles to research attempts in this area: (1) there is a lack of large, known skeletal
samples of subadults and (2) the smaller size of the bones increases the significance of
measurement error. Due to the dearth of juvenile skeletal samples, many of the studies of
sexual dimorphism in subadults have used radiographs, which do not necessarily compare
well with dry bones (
Bass, 1987
).
With adult sex estimation, sexual dimorphism in size can be a useful means of discrimi-
nation within a single population (e.g., diameter of the humeral head). Size differences,
however, are not useful in sex estimation of subadults because males and females mature
at different rates and size dimorphism is not as substantial as in adults. For example, female
infants and juveniles develop faster than males, but male subadults will be larger on average
than females of the same age (
Saunders, 2000; Scheuer and Black, 2004
). Even by the twen-
tieth week in utero, a female fetus is about 10% more developed than a male fetus (
Saunders,
2000
). Weaver explains that sexing a fetus by size can be a tautological exercise, as fetal age is
never a certainty (
Weaver, 1986
).
Two potential research areas show promise in terms of sex estimation in subadults, but
they must be considered simultaneously. These two research areas are (1) analysis of traits
that show early signs of dimorphism and (2) analysis of the dimorphism in the rate/timing
of development. Intrinsic sexual dimorphism develops early in life in the pelvis, cranium,
and teeth. It is likely that only these traits will have any potential success (however limited)
in subadult sex estimation and assessment. Dental development is more similar between the
sexes, but skeletal development is somewhat dimorphic (
Saunders, 2000
).
Hunt and Gleiser
(1955)
compared timing differences in dental and skeletal development using radiographs
and achieved an accuracy rate of 81%. In another study of three diverse population samples,
Franklin and colleagues found that the mandible is not sexually dimorphic in subadults, with
an accuracy rate not much better than chance (59%) (
Franklin et al., 2007
). The accuracy of sex
estimation is undoubtedly lower in juveniles than in adults. Thus, the goal for accuracy
should be at least 75% (which is 50% better than chance) (
Saunders, 2000
). There are differ-
ences in the timing of skeletal and dental growth between subadult males and females,
which, when compared to the few traits that are actually dimorphic could serve as a measure
of sexual dimorphism. This is one area that could use further testing. There is still the
problem of inter- and intraobserver error rates because the sex differences in metrics appear
to be too small for reliable application (
Scheuer and Black, 2004
). Thus, methods that can
increase measurement accuracy (e.g., 3-D digitization) are the goal for subadult sex
estimation.
In subadults, the pelvis is the most sexually dimorphic bone in infancy, but the problem
with sex estimation from the fetal pelvis is measurement error and the standardization of
the position of the bone for measurement. Infant males have longer ilia, ischia, and femoral
necks, whereas infant females have a longer pubis and a wider sciatic notch (
Saunders, 2000
).
These differences mirror the later sexual dimorphism of the pelvis found in adults, according
to
Weaver (1980)
and
Fazekas and K´ sa (1978)
.
Weaver (1980)
tested anthropologists' ability
to estimate sex using the infant pelvis and found it to be unreliable.
Holcomb and Konigsberg
(1995)
investigated the fetal sciatic notch shape and found significant sexual dimorphism, but
the overlap was too great to be effective. Again, any methods that can capitalize on this
