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Population variation in second metacarpal sexual size dimorphism.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 118:378 –384 (2002)
Population Variation in Second Metacarpal Sexual Size
Dimorphism
Richard A. Lazenby*
Anthropology Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
KEY WORDS
second metacarpal; size and shape; activity; adaptation
ABSTRACT
This paper contrasts levels of sexual size
dimorphism in second metacarpal osteometric and geometric morphology in two bioculturally distinctive populations: 19th century Euro-Canadian settlers, and proto/
historic central Canadian Inuit. Significant within-group
sexual size dimorphism is found for all variables, though
few show significant interpopulation differences. However, in every case the Euro-Canadian sample is more
dimorphic than the Inuit sample. Notably, differences reside in geometric measures (total area, Imax) sensitive to
variation in functional strain, and thus are interpretable
in light of proximate causal models, i.e., activity profiles
distinct from generalized mode of subsistence. Other proximate factors, such as nutritional stress acting to diminish
Inuit sexual size dimorphism, may also play a role. However, models often cited to explain dimorphism, such as
marriage practice (e.g., polygyny) or division of labor situated in mode of subsistence, do not. The higher sexual
size dimorphism in the 19th century settler sample belies
the notion that technological progress inevitably leads to
reduced dimorphism. Am J Phys Anthropol 118:378 –384,
2002. © 2002 Wiley-Liss, Inc.
Since the publication of Darwin’s Descent of Man,
and Selection in Relation to Sex (Darwin, 1871),
sexual size dimorphism has occupied a central place
in evolutionary biology. Existing theoretical constructions of sexual size dimorphism are arguably
constraining to a full appreciation of human biocultural variability, as they discount the possibility of
gendered polymorphism vs. sexual dimorphism (Du,
2000; Lazenby, 2000). The concept nonetheless
stands as a keystone in modeling ontogenetic
(Lieberman, 1984; Wilczak, 1998) and phylogenetic
(Plavcan and van Schaik, 1997; Tague and Lovejoy,
1998; Rehg and Leigh, 1999) morphology in past and
present populations. Of course, it is not so much that
male and female are demonstrably, if not obviously,
different, but rather what the differences mean.
While the magnitude of sexual size dimorphism in
modern human populations is not excessively large
(Gaulin and Boster, 1985, 1992; Blackless et al.,
2000), the differences are often significant (Holden
and Mace, 1999) and beg the question: in what ways
and why are male and female dissimilar? Is all dimorphism subject to, or the product of, selection?
How viable are alternatives to strict adaptationist
(Gould and Lewontin, 1979) explanations, e.g., allometry or phenotypic plasticity? The observation
that dimorphism increases with body size with a
slope greater than 1.0 (e.g., Fairbairn, 1997) entails
the former, while behaviorally based models (e.g.,
Ruff, 1987) implicate the latter. Morphologically, the
accepted construction of sexual dimorphism refers to
features of guise (size, shape, and/or pigmentation)
which manifest as secondary sexual characteristics
capable of distinguishing male from female (Frayer
and Wolpoff, 1985). The interpretation of sexual size
dimorphism (and other dimorphisms, e.g., discrete
pathologies; see Sofaer Derevenski, 2000) resolves
causality into proximate and/or ultimate spheres
(i.e., within or between generations), but invariably
is enmeshed within the nexus of biology and culture
(Frayer and Wolpoff, 1985).
The purpose of this paper is to describe the pattern of sexual dimorphism in human second metacarpal morphology as presented in two genetically,
ecologically, and behaviorally distinct populations:
19th century Euro-Canadian pioneers and central
Canadian Inuit. An advantage of exploring dimorphism in second metacarpal morphology in such disparate samples is the obvious and intimate association
of hand anatomy to the technological manipulation of
the environment expressed in sex-specific activities
mediating local (re)modeling of skeletal size and
shape. While sex differences in metacarpal morphology have been studied from the point of view of basic
©
2002 WILEY-LISS, INC.
Grant Sponsor: Natural Sciences Engineering Research Council of
Canada; Grant number: OPG 0183660.
*Correspondence to: Richard A. Lazenby, Anthropology Program,
University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada. E-mail: lazenby@unbc.edu
Received 20 June 2001; accepted 24 January 2002.
DOI 10.1002/ajpa.10110
Published online in Wiley InterScience (www.interscience.wiley.
com).
METACARPAL DIMORPHISM: POPULATION DIFFERENCES
TABLE 1. Demographic profile for the Euro-Canadian
and Inuit samples: osteometric data1
ES
IN
Sex
Left
Right
Pairs
Left
Right
Pairs
Male
Female
Total
108
81
189
109
81
190
100
70
170
51
33
84
51
37
88
40
24
64
1
ES, Euro-Canadian; IN, Inuit.
skeletal biology (Garn et al., 1972; Plato and Purifoy, 1982; Fox et al., 1995; Lazenby, 1998a), growth
and development (Smithgall et al., 1966; Himes and
Malina, 1977; Kusec et al., 1988), aging (van Hemert
et al., 1990; Kimura, 1995; Mays, 2000), and forensic
identification (Meadows and Jantz, 1992; Scheuer
and Elkington, 1993; Lazenby, 1994; Falsetti, 1995;
Smith, 1996), relatively few studies have examined
behavioral correlates of such dimorphism, beyond
questions of sex-differences in patterns of lateral
hand dominance (Plato et al., 1984; Roy et al., 1994).
A previous comparison of Euro-Canadian and Inuit
samples demonstrated significant differences in aspects of Inuit metacarpal osteometry consistent with
thermoregulatory adaptation vis-à-vis Allen’s rule
(Lazenby and Smashnuk, 1999), indicating a selective component. In that study, two-way factorial
ANOVA (sample ⫻ sex) of regression residuals indicated a relatively weak sex effect; however, a direct
comparison of sexual size dimorphism was not undertaken. The present study furthers the investigation of dimorphism by extending the analysis to
include cross-sectional geometric as well as osteometric variation, and by increasing Inuit sample
size by one-third.
MATERIALS AND METHODS
Samples
This study reports levels of sexual size dimorphism in the left and right second metacarpal for
two samples: the well-studied 19th century St.
Thomas’ cemetery sample of Euro-Canadian settlers
from Belleville, Ontario (Saunders et al., 1995b; Lazenby, 1998b), and a sample of late prehistoric Thule
and historic Inuit from the central Canadian Arctic,
hereafter referred to collectively as Inuit (Table 1).
The Inuit sample, curated by the Canadian Museum
of Civilization, derives primarily from Southhampton and Silumiut Islands and adjacent mainland
sites in Nunavut Territory. All are adult individuals,
spanning the age range from osteologically young to
old. For the Euro-Canadian sample, age and sex had
been previously determined with regard to accepted
standards of pelvic and craniodental morphology
(Rogers and Saunders, 1994). In the case of the Inuit
sample, determinations recorded in the Museum
catalogue were confirmed by the author, again with
reference to diagnostic criteria of pelvis and cranium. Although aging has a demonstrable and often
significant effect on bone mass via endocortical loss
379
(Maggio et al., 1997), the variables studied here (see
below) tend to be stable with age (Lazenby, 2002).
While some circumferential periosteal apposition occurs, this tends to be statistically (albeit not necessarily biologically) insignificant (Lazenby, 1990).
Age was thus ignored as an independent variable in
this analysis, aside from its relation to the progression of pathological changes. In both samples, a few
cases exhibited moderate to severe joint margin osteoarthritic changes, and were excluded. Otherwise,
all metacarpals studied appeared morphologically
normal. This is an important consideration, as sexual size dimorphism reflects the modeling and remodeling of bone to varying ecological conditions
throughout life against a genetically determined,
species-specific norm-of-reaction for male and female body size (Rogers and Mukherjee, 1992;
Holden and Mace, 1999). Ecological conditions,
broadly speaking, include components of activity,
endocrinology, nutrition, and pathology. Avoiding
sampling individuals with outward markers of disease stress lends confidence to interpretations of
dimorphism grounded in an biocultural model (cf.
Hawkey and Merbs, 1995; Ruff, 2000).
Variables
This study examined both osteometric and midshaft cross-sectional geometric variation. Osteometric measures included interarticular length (IAL)
and maximum midshaft diameter (MSD), as well as
head width (HW) and base width (BW) in both mediolateral (ML) and dorsopalmar (DP) orientations
(Fig. 1A). The geometric variables studied were total
area (TA), maximum bending rigidity (Imax), and
ratio of maximum to minimum bending rigidity
(Imax/Imin), a functional index of shape in which a
value of 1.0 denotes a circular section (Fig. 1B).
These data were collected from midshaft cross sections, digitalized using SLCOMM (Eschman, 1990).
Details of data collection and error rates are documented elsewhere (Lazenby, 1998b); the total sample size for the geometric data was smaller than that
reported in Table 1 by a few individuals in both the
Euro-Canadian (3 fewer) and Inuit (2 fewer) samples, due to inadequate tissue preservation for preparing cross sections.
Analyses
Sexual dimorphism in skeletal samples is quantified either through direct observation (by measuring
bones of assigned or known sex), or by estimation,
when it is not possible to determine sex for the
sample, as is often the case in paleoanthropological
studies (Rehg and Leigh, 1999). The majority of
studies measuring dimorphism report it as a ratio of
male to female size (or the inverse), often weighted
by the difference of means, or the average difference
of means (Hamilton, 1982). Ranta et al. (1994) argued that ratio measures of sexual size dimorphism
should only be used if the relation of X (male) and Y
380
R.A. LAZENBY
TABLE 2. Sexual size dimorphism for Euro-Canadian
and Inuit samples1
ES SSD
IAL
MLBW
DPBW
MLHW
DPHW
MSD
TA
Imax
Imax/Imin
IN SSD
Left
Right
Left
Right
0.059*
0.127*
0.098*
0.118*
0.097*
0.143*
0.247*
0.555*
0.089*
0.058*
0.128*
0.084*
0.117*
0.108*
0.145*
0.244*
0.542*
0.086*
0.045*
0.135*
0.057*
0.090*
0.109*
0.109*
0.199*
0.436*
0.083*
0.056*
0.118*
0.052*
0.096*
0.108*
0.093*
0.192*
0.405*
0.045*
1
SSD ⫽ ln(M) ⫺ ln(F). SSD, sexual size dimorphism; ES, EuroCanadian; IN, Inuit; IAL, interarticular length; MLBW, mediolateral base width; DPBW, dorsopalmar base width; MLHW,
mediolateral head width; DPHW, dorsopalmar head width; MSD,
midshaft diameter; TA, total area.
* Significant at P ⬍ 0.05.
Size dimorphism was initially evaluated by t-test
within populations. Subsequently, intersample differences were tested using the t-statistic developed
by Greene (1989). All analyses were conducted using
JMP for Macintosh (SAS, 2001), with alpha set at
0.05.
RESULTS
Fig. 1. Osteometric (A) and geometric (B) variables used in
this study. Abbreviations are defined in text. Imax is a measure of
amount and distribution of tissue perpendicular to Imax axis.
Total Area is sum of tissue and cavity space circumscribed by the
periosteal surface.
(female) can be shown to be isometric, i.e., dimorphism is independent of body size. Such criticism is
most appropriate in interspecific studies in which
sexual size dimorphism varies directly over a wide
range of body sizes (Fairbairn, 1997). In a recent
review, Smith (1999) showed that the correlation of
a variety of ratio estimates of dimorphism with female body size were both 1) consistent within datasets (i.e., each ratio produced statistically equivalent
values), and 2) generally low (ca. 0.20 – 0.45), and in
some cases nonsignificant (his Table 5). Smith
(1999), in fact, concluded that ratios are preferred
for analyses of sexual size dimorphism (contrasted,
e.g., with regression residuals, which foster dubious
statistical interpretation). In the present study, sexual dimorphism was calculated using ln(M/F), as
recommended by Smith (1999). Note that ln(M/F) is
numerically equivalent to ln(M) ⫺ ln(F); and in both
cases, “M” and “F” refer to male and female mean
values.
Table 2 reports the difference in sexual size dimorphism within samples. Several outcomes are evident
in this analysis. All differences are positive, indicating the uniformity of greater male dimensions and,
in the case of Imax/Imin ratio, greater male noncircularity. All are significant at P ⬍ 0.05, and typically
at P ⬍ 0.001. The largest differences occur for geometric variables TA and Imax, which measure resistance to compressive and bending strain, respectively, and are typically described as behavioral
indicators (Ruff, 2000). The least dimorphic (though
still significant) measure is interarticular length
(IAL). This is consistent with the observation that
interarticular length invariably contributes the lowest weighting to discriminating male from female
(Falsetti, 1995). Few side differences are evident,
with the possible exceptions of Inuit MLBW and the
Imax/Imin ratio.
Given the presence of significant dimorphism
within samples, the question remains: to what degree do these bioculturally distinct populations differ in pattern of dimorphism? A cursory examination
of Table 2 suggests that some, but not all, variables
exhibit different levels of dimorphism between
groups: DPBW, MLHW, MSD, TA, and Imax are
likely candidates. Table 3 reports on levels of dimorphism and differences between samples. Of interest
here is the observation that, with few exceptions,
dimorphism is greater in the Euro-Canadian sample, though comparatively few of these differences
turn out to be significant (Table 4). Indeed, essentially none of the osteometric measures achieved
significance in the level of interpopulation dimorphism. However, it is noteworthy that the behav-
METACARPAL DIMORPHISM: POPULATION DIFFERENCES
TABLE 3. Difference and directionality for sexual size
dimorphism between Euro-Canadian and Inuit samples1
Left
IAL
MLBW
DPBW
MLHW
DPHW
MSD
TA
Imax
Imax/Imin
Right
ES
IN
IN ⫺ ES
ES
IN
IN ⫺ ES
0.060
0.128
0.098
0.118
0.097
0.143
0.250
0.564
0.087
0.044
0.135
0.057
0.089
0.110
0.109
0.203
0.449
0.088
⫺0.016
0.007
⫺0.042
⫺0.029
0.013
⫺0.034
⫺0.046
⫺0.115
0.001
0.058
0.129
0.086
0.118
0.109
0.146
0.247
0.556
0.093
0.055
0.115
0.048
0.095
0.108
0.093
0.189
0.402
0.043
⫺0.003
⫺0.013
⫺0.039
⫺0.023
⫺0.001
⫺0.053
⫺0.057
⫺0.154
⫺0.049
1
IAL, interarticular length; MLBW, mediolateral base width;
DPBW, dorsopalmar base width; MLHW, mediolateral head
width; DPHW, dorsopalmar head width; MSD, midshaft diameter; TA, total area; ES, Euro-Canadian; IN, Inuit.
TABLE 4. Results of test by Greene (1989) for population
differences in sexual size dimorphism1
Left
IAL
MLBW
DPBW
MLHW
DPHW
MSD
TA
Imax
Imax/Imin
Right
Tg
df
P
Tg
df
P
1.396
⫺0.493
1.872
1.699
⫺1.898
1.615
2.084
1.952
0.000
269
264
255
264
259
269
268
268
268
0.164
0.622
0.062
0.091
0.059
0.107
0.038*
0.052*
1.000
0.554
0.387
1.834
1.424
⫺0.581
2.487
2.124
3.352
1.284
274
268
261
271
269
274
270
270
270
0.580
0.699
0.068
0.156
0.562
0.013*
0.035*
0.001*
0.200
1
Tg, Greene’s t-statistic. IAL, interarticular length; MLBW, mediolateral base width; DPBW, dorsopalmar base width; MLHW,
mediolateral head width; DPHW, dorsopalmar head width; MSD,
midshaft diameter; TA, total area; df, degrees of freedom.
* Significant at P ⬍ 0.05.
ioral geometric markers TA and Imax differ significantly, with greater levels of sexual size dimorphism
characterizing the Euro-Canadian sample.
DISCUSSION
Frayer and Wolpoff (1985) distinguished between
proximate and ultimate causes of sexual dimorphism which, while theoretically exhaustive, are not
mutually exclusive. Proximate models are proximate by virtue of their temporality and ties to environmental disturbances, while ultimate models traditionally reference intergenerational adaptation to
shifting selective forces, primarily cultural. Proximate causation is rooted in notions of nutrition,
secular change, and female buffering (Brauer, 1982;
Stinson, 1985), with ultimate causes framed by selection and adaptation vis-à-vis mating/marriage
patterns, division of labor, and noneconomic role
differences (Gaulin and Boster, 1992; Holden and
Mace, 1999). Proximate models hypothesize that under regimes of nutritional duress, male growth and
development are fettered to a greater degree than in
females, leading to more equitable body size. Such a
response adaptively conserves female body fat
stores, and provides for development of a reproductive anatomy appropriate to conceiving, carrying,
381
delivering, and nurturing viable offspring. Conversely, nutritional well-being increases body size
within the parameters established by ultimate
causal factors, producing more dimorphic morphologies (Brauer, 1982; Frayer and Wolpoff, 1985;
Holden and Mace, 1999). Ultimate models, on the
other hand, are directed by Darwinian concepts of
competition among males for females or “ecological
divergence” related to subsistence. Males are supposedly larger in polygynous societies, an argument
finding little support cross-culturally. Gaulin and
Boster (1985, 1992), for example, observed that human marriage systems most likely have been insufficiently stable through time to permit evolution of
cross-cultural differences in stature dimorphism.
The division of labor hypothesis is popularly invoked
to account for apparently declining levels of sexual
size dimorphism through time, in keeping with the
transition from Upper Paleolithic “big game hunting” requiring large, robust males, through the Mesolithic “broad spectrum” small game/foraging adaptation, to Neolithic agriculture in which the
demands for differential body size were diminished.
Ruff (1987) extended this trend to include the industrial revolution in his analysis of sexual size dimorphism in femoral cross-sectional geometry, noting
that modern peoples were least dimorphic among
his samples. The critique by Holden and Mace
(1999) of the division of labor hypothesis points to
several inconsistencies, including “reverse” transformations (i.e., increasing dimorphism with adoption
of agriculture). Their analysis of ethnographic data
for 76 populations found that stature dimorphism
was related neither to marriage pattern nor mode of
subsistence (i.e., foraging vs. farming). However,
stature dimorphism was negatively associated with
the contribution of women’s work to subsistence:
women were taller, and dimorphism reduced, in societies in which they contributed more to food production. Holden and Mace (1999, p. 42) concluded
that “in contemporary humans, neither hunting nor
agriculture has any effect on sexual dimorphism. It
is the amount of subsistence work done by men and
women, rather than the type of subsistence practiced, which has an effect.” They suggested that this
increased contribution may have translated into better female nutrition, and more equitable male-female body size, an argument invoking proximate
causation and intrinsic morphological plasticity.
While such arguments apply to global sexual size
dimorphism referents such as stature or mass, they
are less aptly applied to discrete morphologies such
as those of the second metacarpal investigated here.
Finer grade distinctions need to be made: amount
and type of activity within mode of subsistence are
relevant factors. In the present study, significant
levels of dimorphism were found within populations,
and significant interpopulation differences were
found for geometric measures that are generally
considered sensitive indicators of functional adaptation and the bone modeling response (Ruff, 2000).
382
R.A. LAZENBY
The greater dimorphism in the Euro-Canadian sample
for geometric measures broadly reflective of greater
compressive, bending, and torsional strength would
indicate a greater difference in the quantity (magnitude and/or frequency) of functional loading between
Euro-Canadian males and females compared to
Inuit males and females. Support for this conclusion
requires consideration of ethnographic and historic
data.
The parish of the St. Thomas’ Anglican Church
cemetery, from which the Euro-Canadian sample
was recovered, was predominantly rural, particularly in the early decades of its existence (Saunders
et al., 1995b). However, by the middle of the century,
Belleville had grown to become an urban (albeit
frontier) center of over 4,500 individuals, reaching
almost 7,500 persons by 1874 when the cemetery
closed. The Euro-Canadian skeletal sample would
most certainly contain people with a wide variety of
life experience, from the farming, mining, manufacture, service, domestic labor, and administrative
sectors, among others (Saunders et al., 1995a). Such
diverse experiences would have been registered not
only among different individuals in the sample, but
very likely (in some cases) within the life history of
single individuals. The impact of such life-experience variation on metacarpal sexual dimorphism is
difficult to ascertain, but from a population standpoint would be most significant in the event of systematic bias for greater numbers of “ladies” and/or
fewer “gentlemen” among those interred, both of
which would produce increased levels of dimorphism. However, there is no reason to suspect that
this was the case, particularly in the early years
when the St. Thomas cemetery was the only available burial ground, receiving individuals of diverse
backgrounds (Saunders et al., 1995a). In any case,
such a consideration entails an analysis of class,
which lies beyond the scope of the present sample.
Thus, the greater dimorphism in the Euro-Canadian
sample may be an artifact of comparatively reduced
dimorphism in the Inuit sample.
Ethnographic accounts of Inuit social and economic life document activities that are typically
male (large-game hunting/fishing, and construction
of housing, boats, and sleds) or typically female
(gathering, small-game hunting/fishing, and processing skins for clothing and housing), and note
that sexual division of labor occurred at an early age
(Steen and Lane, 1998). Hawkey and Merbs (1995)
examined markers of occupational stress in a skeletal series from the central Canadian Arctic, including sites contributing individuals to the present
study (e.g., Kamarvik and Silumiut). Their results
for the upper limb indicated “a dichotomy of labour
between the sexes consistent with ethnographic information” (Hawkey and Merbs, 1995, p. 330). They
noted, for example, that early-period Thule females
tended to use upper limb muscle groups associated
with preparation of skins and unilateral rowing
(e.g., of umiaks rather than paddling kayaks as done
by males), while later-period male markers of occupational stress reflected activities such as “harpooning at a downward angle” (Hawkey and Merbs, 1995,
p. 331), as well as “kayaker’s clavicle,” represented
by a distinct J-shaped lesion at the costoclavicular
ligament insertion. However, Stefansson (1919,
cited in Giffen, 1930) notes that the exceptional
complementarity of technical tasks often translated
into Inuit men doing any kind of women’s work and
vice versa. Furthermore, it is risky to generalize
lifeways for past populations on the basis of their
residence in a particular geographic region, especially one such as the Arctic known to vary widely
regionally vis-à-vis resource availability and climate
(Moran, 1981). Steen and Lane (1998), for example,
found population-specific differences in musculoskeletal stress markers between males and females
for two Bering Sea archaeological samples. Musculoskeletal stress marker (and hence activity pattern)
differences for these samples reflect both geographic
and temporal factors (one postcontact island with an
emphasis on marine resources, and one prehistoric
coastal mainland with a marine and terrestrial focus).
In this study, significant sexual size dimorphism
was found within the Inuit sample, but compared to
the Euro-Canadian sample, levels of dimorphism
were significantly lower for measures of bone
strength and rigidity. Such an outcome could accrue
through reduced male size and/or increased female
size: the former possibly an outcome of nutritional
stress (see below), and the latter through greater
female labor. While such effects may have been insufficient to render within-group dimorphism insignificant, they could explain the relatively lower intergroup result.
It is interesting that Holden and Mace (1999)
found that Native North Americans, including Central Canadian Inuit (e.g., Copper and Iglulik data
published by Jenness, 1923), exhibited the greatest
degree of sexual dimorphism in stature among their
76 ethnographic samples. As noted above, they
found overall that women were taller in cultures
with greater female contribution to subsistence, and
their finding of high dimorphism among the Inuit
would suggest that female Inuit were not major
contributors to subsistence. One might ask, however, to what degree preparing hides and sewing
clothing for male hunters contributes to the success
of Inuit food production. There are also methodological issues concerning stature: given the effective
operation of Bergmann’s and Allen’s rules, is the
relevant measure for Inuit standing height or sitting
height? On a further methodological note, their use
of regression residuals to measure size dimorphism
is problematic (Smith, 1999), as alluded to above.
These criticisms aside, Holden and Mace (1999)
highlighted the probability that different anatomical regions and morphologies present different patterns of dimorphism consistent with evolutionary
mosaicism and plasticity. This conclusion is rein-
METACARPAL DIMORPHISM: POPULATION DIFFERENCES
forced by noting that the hand of 19th century rural/
urban Euro-Canadians is more dimorphic than that
of hunting Inuit, contra the argument for decreasing
dimorphism in femoral cross-sectional geometry
with the adoption of more modern lifeways (Ruff,
1987).
Two additional factors may have important consequences for the results found here. First, could
differences in overall body size between the populations compared underlie the greater Euro-Canadian
dimorphism? This argument would be plausible
were the level of dimorphism uniform across all
variables. However, while the Euro-Canadian sample
was consistently more dimorphic, not all measures
were significantly so. Indeed, some (e.g., interarticular
length) showed little intra- or interpopulation dimorphism, belying the importance of allometric effects for
nonweight-bearing elements. Moreover, nutritional
factors may have diminished the level of dimorphism
in the Inuit sample, given ethnographic accounts of
intermittent famine among Arctic populations (Shephard and Rode, 1996). Stress affecting growth tends to
preferentially impact males, resulting in reduced body
size dimorphism (Stinson, 1992). Holden and Mace
(1999) argued that nutritional differences cannot
account for all cross-cultural variation in sexual size
dimorphism; for example, they observed that North
American natives are frequently more dimorphic
than more nutritionally replete Europeans. All the
same, it is quite likely that the Euro-Canadian sample had more consistent access to quality nutrition
than the Inuit (ignoring factors of class among EuroCanadians, beyond examination in this study).
Again, however, if this is the case, why would it
diminish size dimorphism in only those measures
intimately involved in labor, and not others (e.g.,
articular dimensions)? One possible explanation resorts to arguments that tubular bone diaphyses are
more plastic, and environmentally labile, than articular dimensions (Ruff, 1988; Ruff and Runestad,
1992). The latter are constrained to preserve size
and shape by the necessity of maintaining joint integrity. One wonders whether there may be a species-level baseline dimorphism observable in such
anatomies as articular dimensions.
CONCLUSIONS
Combined osteometric and geometric analysis of
metacarpal morphology indicates significant interpopulation dimorphism. Dimorphism was localized
in more functionally labile geometric measures. The
magnitude of dimorphism seen in the behaviorally
diverse Euro-Canadian sample exceeded that for the
Inuit, a population with marked though not proscriptive division of labor and harsh conditions of
existence. Certainly, the differences in sexual size
dimorphism between these two groups cannot be
explained with regard to ultimate causes such as
marriage practices: the more dimorphic 19th century Anglicans could hardly be considered polygy-
383
nous, a label variously applicable to the less dimorphic Inuit (see Damas, 1984).
The conclusion of this study is that in the EuroCanadian sample, both qualitative and quantitative
aspects of behavior were significant contributors to
metacarpal dimorphism. Men and women did different things, to different degrees. Among the Inuit,
the operative aspect was fundamentally quantitative, as Inuit men and women were likely to have
shared many tasks. In this sense, a modified “division of labor” explanation contextualized by activity
profiles rather than mode of subsistence is a more
applicable interpretative framework for cross-cultural comparisons, particularly given the intractable question of class in 19th century Upper Canada.
While the morphological attributes examined here
can only be considered nonspecific indicators of differences in behavior between males and females,
they are nonetheless strong indicators of behaviorally mediated activity differentials within and between populations.
ACKNOWLEDGMENTS
The support of the Canadian Museum of Civilization and its Curator of Physical Anthropology, Dr.
Jerome Cybulski, is gratefully acknowledged. The
comments of two anonymous reviewers and Dr.
Emőke Szathmaáry provided for a much improved
paper.
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