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

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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: [email protected] 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-a`-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

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(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

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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-a`-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,

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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).

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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-a`-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-

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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. Emo˝ ke Szathmaa´ ry provided for a much improved paper. LITERATURE CITED Blackless M, Charuvastra A, Derryck A, Fausto-Sterling A, Lauzanne K, Lee E. 2000. How sexually dimorphic are we? Review and synthesis. Am J Hum Biol 12:151–166. Brauer G. 1982. Size sexual dimorphism and secular trend: indicators of subclinical malnutrition? In: Hall RL, editor. Sexual dimorphism in Homo sapiens. A question of size. New York: Praeger Scientific. p 245–259. Damas D, editor. 1984. Arctic. Handbook of North American Indians, volume 5. Washington, DC: Smithsonian Institution. Darwin C. 1871. The descent of man, and selection in relation to sex. London: J. Murray. Du S. 2000. “Husband and wife do it together”: sex/gender allocation of labor among the Qhawqhat Lahu of Lancang, Southwest China. Am Anthropol 102:520 –537. Eschman P. 1990. SLCOMM: a user-supported real-time digitizing package. Alberquerque, NM: Eschman Archaeological Services. Fairbairn DJ. 1997. Allometry for sexual size dimorphism: pattern and process in the coevolution of body size in males and females. Annu Rev Ecol Syst 28:659 – 687. Falsetti AB. 1995. Sex assessment from metacarpals of the human hand. J Forensic Sci 40:774 –776. Fox KM, Kimura S, Powell-Threets K, Plato CC. 1995. Radial and ulnar cortical thickness of the second metacarpal. J Bone Miner Res 10:1930 –1934. Frayer D, Wolpoff MH. 1985. Sexual dimorphism. Annu Rev Anthropol 14:429 – 473. Garn SM, Frisancho AR, Sandusky ST, McCann MB. 1972. Confirmation of the sex difference in continuing subperiosteal apposition. Am J Phys Anthropol 36:377–380. Gaulin SJC, Boster JS. 1985. Cross-cultural differences in sexual dimorphism. Is there any variance to be explained? Ethnol Sociobiol 6:219 –225. Gaulin SJC, Boster JS. 1992. Human marriage systems and sexual dimorphism in stature. Am J Phys Anthropol 89:467– 475.

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Population variation in second metacarpal ... - Wiley Online Library

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 geo- metric morphology in two ...

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