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Totem: The University of Western Ontario Journal of

Volume 22 | Issue 1 Article 3

2014 Mating Behavior in and Early : A Review of The Diagnostic Potential of Dental Dimorphism. Joseph J. Werner University of Alberta, [email protected]

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Recommended Citation Werner, Joseph J. (2014) "Mating Behavior in Australopithecus and Early Homo: A Review of The Diagnostic Potential of Dental Dimorphism.," Totem: The University of Western Ontario Journal of Anthropology: Vol. 22: Iss. 1, Article 3. Available at: http://ir.lib.uwo.ca/totem/vol22/iss1/3

This Article is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Totem: The nivU ersity of Western Ontario Journal of Anthropology by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Mating Behavior in Australopithecus and Early Homo: A Review of The Diagnostic Potential of Dental Dimorphism.

Abstract Dental dimorphism is one of the primary means by which the mating systems of extinct hominins are studied. Its use has been particularly significant for describing the behaviors of Australopithecus and early Homo, and consequently the factors involved in the evolution of our own . Analysis however, has tended to produce ambiguous and contrasting results, with no firm agreement as to what mating strategies these genera practiced. Interpretation is confounded by numerous problems such as a generally poor understanding of how dental dimorphism develops in , and what factors influence its expression. It is also not well known how these factors interact with different aspects of the dentition and to what relative extent these aspects are diagnostic of mating behavior. The failure in many cases to firmly establish the sex of fossil specimens has likewise hampered the interpretations of and by extension, mating behavior. Lastly, the ability to correlate dental dimorphism with mating systems, even in living primates, has met with only moderate success. For these reasons it is argued that dental dimorphism be used only to support the most general assertions about hominin social behavior.

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Acknowledgements The ubmitts ed paper benefited greatly from the input of Dr. Lesley Harrington, whose comments and assistance were invaluable.

This article is available in Totem: The nivU ersity of Western Ontario Journal of Anthropology: http://ir.lib.uwo.ca/totem/vol22/ iss1/3 Werner: Mating Behavior and Dental Dimorphism in Australopithecus and Early Homo

Mating Behavior in Australopithecus and however is still highly varied and a number Early Homo: A Review of the Diagnostic of dramatically different mating strategies Potential of Dental Dimorphism have been proposed, including: single- male/multi-female, multi-male/multi-female, J. Jeffrey Werner and monogamous systems. While using dentally dimorphic traits such as canine Introduction height as a proxy for mating behaviour is During the and Lower common in palaeontology, it is nevertheless (5.2 – 1.5 million ago), the problematic for a number of reasons. Firstly, ancestors of modern experienced a the influence of alternate sources of dental significant change in body size and dimorphism such as diet, intra-female proportions, which is believed to have competition, correlated response, and resulted in a more -like pattern of 1 predator defense are not well understood and sexual dimorphism (Anton and Snodgrass rarely accounted for in predictions of mating 2012; McHenry and Coffing 2000; Spoor et behaviour. This makes detecting and al. 2007). These changes are consistent with isolating morphological differences caused reduced male intrasexual competition and by sexual selection from these alternate are thought to signal a change in mating sources of variation difficult if not behaviour from a form of polygyny to impossible. Secondly, unrelated dimorphic monogamy (Strier 2007). Understanding attributes, such as canine-size and body-size, how sexual dimorphism was related to are the result of dissimilar selective process mating systems and social behaviour in and may consequently represent different these species is therefore crucial for aspects of the social and environmental determining how and why the contemporary context. Furthermore, the relative diagnostic human pattern of sexual dimorphism value of each of these measures has yet to be evolved. fully determined, which makes comparisons In addition to body size, sexual with living, analogous species difficult. differences are also commonly expressed in Thirdly, disagreement over species the teeth of dimorphic , such as classification, and low sample sizes also primates, and are one of the most powerful prevent a secure sex estimation of individual means of identifying the group composition specimens, confounding current and mating systems of paleo-species understandings of sexual dimorphism in (Gordon, Green, and Richmond 2008; Australopithecus and early Homo. Lastly, Hillson 1996; Kay et al. 1988; Strier 2007; even in living species, mating Wolpoff 1976; Wood, Li, and Willoughby systems correlate only modestly well with 1991). The dimorphic of primate observed sexual dimorphism, which is only dentition is especially important for the further complicated paleontologically by the study of hominin genera such as three previous factors. Australopithecus and early Homo, for which For the reasons listed above, it will teeth are preferentially preserved due to the be argued that the dimorphic dentitions of resilient properties of relative early hominin taxa are not always strong to bone (Conroy 2005). The interpretation of indicators of intrasexual conflict intensity or the dental evidence for these genera mating behaviour by themselves and that

1 they must be used in association with other Sexual dimorphism refers to the differences in size, dimorphic characters. morphology, colouration, and behaviour of males and females of the same species. (Strier 2007)

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are composed of an equal member-ratio of both sexes, and generally practice a form of Background: Sociobiology and Sexual polygyny. The intensity of competition Dimorphism between males differs between multi- In primate species, sexual dimorphism male/multi-female species, resulting in develops primarily as a result of sexual highly variable levels of sexual dimorphism selection, which exerts unalike pressures on between taxa. In primate social groups that males and females, as each sex competes in practice monogamous pair-bonding, or its own fashion to reproduce successfully polyandry, males and females are of (Strier 2007). This of competition is comparable size and morphology, taking more studied in males where it has been equivalent roles in the defence of their shown to contribute most substantially to territory and the care of their offspring. size dimorphism (Plavcan 2012b). Contests Monogamous and polyandrous primates are between males for access to mates are rare compared to those that practice other frequently typified by physical force, mating strategies. displays of dominance, and elaborate performances. If, in one of these arenas, a Dental Variation as a Result of Sexual heritable trait increases male reproductive Selection success, selection favours it. As a result, in Male and female body-size many primate species, males are larger than coefficients are one of the most recognizable females and support a more elaborate array examples of sexual dimorphism, but sex of weaponry and ornaments (Wilson 1975). dependent disparities in tooth-size and morphology also form the basis of The effects of intrasexual conflict tend to predictions regarding the social organization produce similar patterns of morphological and mating behaviour of primate species adaptation which are visible at a taxonomic (Plavcan 2001). For example, some scholars scale and can be systematized in semi- have suggested that the size of the posterior predictable ways. Primatologists typically teeth (pre-molars and molars) in non-human recognize two to three primary types of primates is a viable indicator of body-size mating systems, each partly identifiable by and thus body-size dimorphism (Hillson the degree of sexual dimorphism, and 1996; Wolpoff 1976). Despite the effects of intrasexual conflict intensity that is exhibited diet (metabolic scaling factors) on crown (Harvey, Kavanagh, and Clutton‐Brock dimensions, the size of the molars, and to a 1978; Plavcan 2001; Strier 2007). lesser extent the pre-molars, appear to scale allometrically to the size of the organism. A common classification scheme is That is, the posterior teeth remain roughly laid out by Strier (2007), who recognizes proportional to the rest of the as three divisions. Firstly, single-male/multi- body-size changes (Gingerich 1977; female groups are characterized by a Gingerich, Smith, and Rosenberg 1982; dominant male who presides over a Hillson 1996; Wood 1979). Although particular community, often debarring other research on other animal species, such as males from the group entirely. With only birds, has revealed significant differences in one male permitted to mate, competition is the size and shape of feeding structures highest in this group structure, and single- between males and females who occupy male/multi-female groups produce the most different dietary niches, primates subsist on extreme examples of sexual dimorphism. similar foods irrespective of sex and thus do Secondly, multi-male/multi-female groups not exhibit divergent dietary adaptations

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(Plavcan 2001). Simply then, a larger 1996; Strier 2007; Wilson 1975; Wolpoff primate species would be expected to have 1976; Wood, Li, and Willoughby 1991). larger molar teeth than a smaller one; and similarly, males of a greater size would be Dental Dimorphism in Plio-Pleistocene anticipated to possess larger molars than Hominins (5.2-1.5 mya) females of a smaller size. This relationship The earliest identified members of is thought to allow the relative tooth sizes of the Homo ( / Homo the posterior dentition in non-human rudolfensis) were in place in by primates to serve as a rough proxy from at least the beginning of the Pleistocene which to infer body-size differences and around 2.6 million years ago (mya) (Bobe thus conflict intensity (Wolpoff 1976). Like and Behrensmeyer 2004; Wood 1996). other tooth classes however, the size and While this group is often distinguished by an morphology of the posterior dentition expansion in brain volume, their post-cranial responds to factors other than conflict morphology remained very similar to their intensity; such as diet. What is more, pre- likely precursors, the , molars and molars are less representative of who evolved in South and East Africa dimorphic distance (when scaled for size) during the Pliocene (5.3-2.6 mya). Both relative to other types of teeth (Hillson Australopithecus and early Homo shared a 1996). mixture of primitive and derived features which suggest a mixed adaptation to As the posterior dentition tends to be terrestrial as well as arboreal life monomorphic, unless an extreme difference (Stringer and Andrews 2005). Many in male and female body-size exists, the scholars also propose that the range of relatively dimorphic buccolingual diameter2 sexual dimorphism exhibited by these and height of the canines is thought to make species was large, easily matching and them a better indicator of inter-male conflict possibly exceeding the maximum intensity (Hillson 1996). Enlarged canine dimorphism observed in surviving primates teeth are hypothesized to be particularly such as and (Gordon, important for males as they double as Green, and Richmond 2008; Grine et al. weapons in direct physical competition with 2012; Hausler and Schmid 1995, 1997; other males, or as a means of Lockwood et al. 1996; Plavcan 2001, 2012; communicating dominance (Harvey, Tague and Lovejoy 1998; Wolpoff 1976). It Kavanagh, and Clutton‐Brock 1978; Hillson follows from what is known about sexual 1986; Sperber 2013; Strier 2007). dimorphism in extant primates that fierce male intrasexual competition typified these Despite inherent difficulties, many two genera and likely revolved around a researchers argue that since not all primates form of polygynous group structure. are uniformly dimorphic, differences in the size of their canine and posterior teeth High levels of dimorphism in should allow paleoanthropologists to make Australopithecus and Homo is supported in assumptions about the relative intensity of part by measurements of their dentition. intrasexual competition in extinct species, When plotted in aggregate, the posterior and relate it to other forms of social tooth-size of these hominins shows a bi- behaviour and group structure (Hillson modal pattern, likely indicating a significant difference in the body-mass between sexes

2 (Wolpoff 1976). What is contradictory is The diameter of the tooth measured from the side closest to the tongue to the side closest to the lips. that while the posterior dentitions of these

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taxa were highly dimorphic, the differences Alternate Sources of Dental Variation in their canine-sizes were much less In order to reliably predict mating pronounced than those of living , though strategy on the basis of sex dependant still somewhat in excess of human averages morphology, a firm understanding of sexual – a pattern that is unique in primatology dimorphism and its causes needs to be (Lee 2005). What is perplexing about this established. One of the primary challenges template is that exaggerated body-mass of identifying sexual dimorphism in hominin dimorphism, predicted by a disparity in taxa is distinguishing sex dependent cheek teeth size and post-cranial remains, is morphology from variation derived from associated most often with high levels of other sources. These additional sources are competition, while recessed canines are often poorly understood, and while male- assumed to be evidence of low levels of male competition is theorized to account for intrasexual competition. This pattern has yet ~48% of the dimorphic morphology of to be satisfactorily explained, but based on primates, the remaining variation is not well numerous analyses Australopithecus and explained (Plavcan 2012b). early Homo are thought to have practiced a range of mating strategies, from single- Until recently it was frequently male/multi-female mating at one extreme, to assumed, for instance, that sexual monogamy at the other (Plavcan 2012b; dimorphism was the result of a Reno et al. 2010). The high variance of these transformation to male morphology away interpretations is symptomatic of a number from an expected ecological optimum of key complications. Namely, that there are (represented by female morphology). More numerous alternate sources of variation recently, however, researchers have begun to capable of impacting the development of evaluate the contributions of female sexual dimorphism which are not often well morphology to sexual dimorphism (Plavcan accounted for. These factors also influence 2004). In particular, female canine-size has different aspects of the dentition unequally, been demonstrated to alter in response to the resulting in mixed or contradictory signals. intensity of resource competition with other Furthermore, doubt over the sex of females. Unlike males, for whom the individual fossil specimens destabilizes the primary source of conflict is for access to already questionable correlations between mates, females compete most intensely for dimorphic dentition and mating systems. food. Consequently, in habitats where Lastly, even in living primates where direct persistent or seasonal circumstances comparisons are possible, dental contribute to scarce or patchy food dimorphism shows only weak to moderate resources, competition between females is concomitance with mating behaviour. The more intense, and female canine-size is following sections describe these issues in exaggerated (Plavcan 2012b). more detail as they pertain to the mating Additional social factors have also systems of the hominin genera been shown to affect the size of primate Australopithecus and Homo. It will be canines. Plavcan and colleagues (1995) advised that researchers avoid directly provided evidence that canine-size correlating patterns of dental dimorphism in dimorphism is reduced in primate social extinct species with mating systems without groups in which males typically form consideration for these additional sources of alliances to determine the outcome of variation. conflict. In such cases, it is hypothesized

that the combative fitness of any one male is

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less important than the total fighting strength becomes selectively neutral, that is, it is not of the group and his ability to form alliances. favoured or deleterious; it will tend to persist Sex dependent roles and behaviour may also in a species unchanged. This phenomenon exaggerate the dimorphic differences of the may result in a selectively neutral, dentition (Leutenegger and Kelly 1977). As dimorphic characteristic becoming preserved males in most primate social groups tend to despite a change in behaviour. be larger, with over-sized canines as a result of sexual selection, they are also better Given that both male and female suited to defend against, and discourage dentitions are sensitive to social and attacks from predators. Because canines are environmental conditions; it is difficult to effective weapons against both predators and know to what extent any particular antagonistic males of the same species, they manifestation of sexual dimorphism is the are twice as likely to be selected for in males result of intrasexual competition as part of a whose role it is to protect the group (Shine specific mating system. As these alternate 1989). Such behaviours are, of course, factors are as likely as not to go undetected invisible paleontologically, and the effects in a fossil context, sexual dimorphism can of alliance making and predator defense on only be partially accounted for, making an canine size are likely to go unrecognized. accurate determination of mating system with current models challenging. Particular characteristics of genetic inheritance may also contribute to the Problems Interpreting Mixed Dimorphic expression of sexual dimorphism. Indicators Autosomal genes are those that are common Because many elements of the to both sexes and, like other genes, may hominin post-cranial skeleton and dentition become selected for under favourable are dimorphic, their relative ability to environmental and social conditions. When indicate aspects of social behaviour, such as characters determined by autosomal genes mating strategy, remains to be fully become selected for in one sex, because they determined. Moreover, as the selective are shared, an associated change in the pressures which act on particular dimorphic opposite sex occurs - an effect called elements of the skeleton are unalike, the correlated response (Lande 1980). This is respective morphology of these elements is hypothesized to mitigate, to some degree, almost certainly reflective of different the effects of sexual selection on dimorphic conditions and causes (Plavcan 2012b). The attributes. For example, if selection favoured diversity of potential causes has made large male canines as a result of intrasexual comparing and interpreting the dimorphic competition, this same trait would likewise dentitions of Australopithecus and early be inherited by any female offspring until Homo difficult because of the mixed and the genes became decoupled as a result of ambiguous behavioural signals that have additional genetic mechanisms. emerged. A key example of this is the Problematically, it is not clear as to how and posterior dentitions of these genera which to what extent this phenomenon impacts the predict extensive body-size dimorphism, differences between sexes (Plavcan 2012b). intrasexual male conflict, and likely a The precise effects of another evolutionary mating system akin to the polygyny process called phylogenetic inertia on sexual observed in many living primates. This dimorphism are similarly unknown (Wilson interpretation is contradicted by the height 1975). Phylogenetic inertia is a mechanism and breadth of the canine teeth which are for morphological stasis: if a heritable trait relatively monomorphic, suggesting low

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conflict levels. This pattern is not Alternatively, Reno et al. (2003, explainable by sexual selection alone, which 2005, 2010) criticize previous studies of cannot easily account for these divergent drawing comparisons between fossil signs. It is clear that the canine teeth and the materials from significantly different spatial posterior dentition are aligned with different and temporal contexts. The improper scale processes and therefore do not represent of analysis, they argue, has resulted in evidence of the same selective pressures. normal temporal and spatial variation being While it has not yet been determined mistakenly identified as sex differences. To precisely what was responsible for forcing correct for these problems, their work has this pattern, it is likely that factors focused on the hominin remains from AL supplementary to mating behaviour and 333 (Hadar, ), a death assemblage mate competition, resulted in the dimorphic dated to 3.2 mya. The remains at this site are character of these species. argued to be a demographically representative sample of A. afarensis, For Wolpoff (1976) and others including both males and females of varying (McHenry 1992, 1994a; Toth and Schick ages. What Reno and colleagues (2003) 2009; contra: Lovejoy 2009; Plavcan 2001, observed are low levels of body-size 2012), the apparently conflicting evidence dimorphism, in agreement with the low can best be explained by the emergence of degree of canine dimorphism already material culture during the Pliocene, leading witnessed in this group. In opposition to to the diminished role of canine teeth as they existing notions, their findings support a were supplanted by extrasomatic means. Not more human-like level of sexual dimorphism only were cultural items argued to be more in A. afarensis. Moreover, Reno et al. (2003) effective in cases of physical conflict, but make the assertion that the minimal sexual that by brandishing them, early hominins dimorphism revealed both dentally and could intimidate their rivals in a manner skeletally at AL 333 is indicative of a functionally equivalent to canine teeth monogamous mating strategy. (Gruter 1982; Wolpoff 1976). Because of the assumed simplicity of these early The continuing disagreement over artefacts, a large body-size remained an the classification of Australopithecus and important factor in the use of early tools and early Homo is largely symptomatic of the weapons, and consequently large, robust problematic nature of collectively males continued to be selected for whereas interpreting individual indicators of their enlarged canines did not. While the dimorphism without consideration for their tool-use theory is plausible, little direct independent causes. This practice has the evidence of this hypothesis, such as skeletal paradoxical effect of reducing certainty trauma has been recorded, and what does about past behaviours as more lines of exist cannot be linked to male/male evidence are compounded (Plavcan 2012). violence, let alone the use of artificial Despite being recognized early by authors weapons (Berger 2012; Susman 2008). such Leutenegger and Kelly (1977) in their Others have also pointed out that the study of primates, little theoretical or beginning of the archaeological record and methodological headway has been made the process of canine reduction in our towards resolving the issue. More recently, ancestors was non-contemporaneous by at Plavcan (2000; see also: Lee 2005; Plavcan least a million years (Plavcan 2001). and van Schaik 1997a) likewise finds in his review of the sexual dimorphism of living and extinct primates, that the occlusal-size

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dimorphism of the canines is much less human anatomy, making the use of sex demonstrable of dimorphic distance than estimation models derived from either of canine height or breadth. Here, even within these taxa prone to error. Moreover, many the same tooth class, different methods of fossils, such as ST 14 (A. africanus) show measuring dimorphism produced varying significant evidence of plastic deformation, results. In order to more accurately assess further complicating the picture (Berge and dimorphic differences, and their correlates Goularas 2010). such as mating systems, a better understanding of key individuators, and how As determining the sex of they interact to produce sexual dimorphism, pelvic remains has proven is required. to be inconsistent, alternate techniques have been employed with varying degrees of Determining the Sex and Ancestry of Fossil success, most of which focus on post-cranial Hominins size metrics and dento-cranial features A necessary prerequisite to (Hager 1990; Tague and Lovejoy 1998). effectively evaluating sexual dimorphism is Since dimorphism in early hominins is the ability to reliably differentiate male and predicted to be substantial, body-size and female anatomy. While the sex of individual robusticity are commonly employed specimens ought to be known at the outset predictors of sex. Conversely, significant of analysis, it is not always the case, and the post-cranial differences may reflect sexes of many fossils are highly provisional. interspecific rather than sexual variation, The difficulty stems principally from a lack and the reliability of this strategy is of fossil remains, which makes evaluating questionable given that many of the intrinsic population variation and sex specimens under study have not yet been differences nearly impossible. classified, without contention, at the level of species (Häusler and Schmid 1995, 1997; In modern humans, analysis of the Miller 2000; Tague and Lovejoy 1998; pelvis is the most accurate method of Wood and Quiney 1996), or even genera in diagnosing sex. Because the morphology of some cases (Susman 2008). The dimorphic the female pelvis must balance the dentition of hominin conspecifics is likewise conflicting requirements of locomotion and used as a sex indicator. This practice is parturition, marked differences relative to problematic for the same reasons that body- the male pelvis are apparent to analysts who size dimorphism is; namely, it is still unclear have demonstrated a high degree of success as to how these specimens should be differentiating them. Post-cranial elements assigned taxonomically, and it is very are, however, quite rare in the Plio- possible that the sex differences identified Pleistocene, and few pelves have been presently may in fact be examples of recovered from which more definitive sex interspecific ones, if not some other form of determinations might be attempted. Even variation. when pelves are recovered (A. afarensis and A. africanus), current methods of sex Given the insecurity of sex estimates assessment are not yet reliable enough to in australopithecines and early confirm the sex of these specimens (Häusler representatives of Homo, the likelihood of and Schmid 1995). The pelvic morphology dependably describing sexual dimorphism of Australopithecus is simply not well and by extension mating behaviours in these understood, and what is known, seems to species is poor. What is more, estimating the suggest divergence from both and sex of specimens on the basis of a priori

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notions of dimorphism introduces a degree that while extreme dimorphism was strongly of circularity as these sex estimations are diagnostic of a polygynous system of then often used to make further statements mating, that the opposite was not true. Thus, about sexual dimorphism. species characterized by low levels of dimorphism were not, as a rule, Sexual Dimorphism in Extant Primates monogamous or polyandrous. The The use of analogs to model complex generalization is even more weakly or unobservable processes is a common expressed in the dimorphic dentition of scientific practice. In the context of different species. Although body-size palaeoanthropology, the study of extant dimorphism is a strong predictor of primates is essential to the development and polygyny and extreme competition among refinement of paleontological theories males, “modest or low degrees of canine- through direct observation (Plavcan 2000). size dimorphism can be found among Compared to the human lineage, which is species with a wide variety of mating thought to be relatively derived, the branch systems and competition levels” (Plavcan that resulted in the great apes, is often 2000: 341). The high levels of variance that assumed to be evolutionarily static – a were revealed in this study demonstrates the retention of the primitive form (White et al. inability of current approaches to detect and 2009). As a result, the hominin taxa near to account for the influence of alternate factors, the base of this branching point are thought exclusive of sexual selection, even in living to be comparatively more ape-like than forms, let alone fossil ones. human-like, creating the impression of morphological closeness with living apes, Conclusions and lending credibility to their use as Hominin sexual dimorphism has analogs. While allowing valuable insight been a focus of paleoanthropological study into primate behaviour, direct comparison for nearly half a century, and though the between living and extinct hominins is not strength of some morphology-behaviour without risk. Great ape evolution is even less correlates have been criticized (Begun 2004; well understood than , and Plavcan 2000, 2001, 2012; Plavcan et al. though great apes are sometimes considered 2005; Rowell and Chism 1986), dental traits to be relatively unchanged from their last such as canine-size continue to serve as common ancestor with humans, research has proxies for mating systems. On the basis of demonstrated that a substantial degree of the extensive posterior tooth-size/body-size differentiation has occurred over the 5-8 dimorphism detected in a number of species million years of evolution that separate these of Australopithecus and early Homo, it is taxa (Grehan 2006). theorized that these genera practiced some form of polygyny, characterized by intense Although dental dimorphism is intrasexual competition between males for easier to study in extant species than fossil access to mates. The low expression of ones, it is still far from a perfect predictor of canine-size dimorphism in these species mating systems in living primates. Plavcan alternatively indicates low competition (2000) showed that not only were different levels and possibly a form of monogamy. dimorphic indicators non-uniformly capable This unique dental pattern has yet to be fully of predicting systems of mating, but that in explained and shows only weak correlation general, sexual dimorphism could only be with the mating systems of living primates. moderately correlated with mating behaviour. Furthermore, it was discovered

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Understanding the relationship heritable processes, and sex roles impact the between sexual dimorphism and mating development of dental dimorphism. By behaviour in these genera is critical to better accounting for these processes it will comprehending how the dimorphic become more feasible to detect and interpret morphology of modern humans originated. the differences produced by conflict Nevertheless, consistent problems have intensity and mating behaviour. Of equal impaired attempts to reconstruct it. For one, importance, separate dimorphic characters many sources of variation are not well must be evaluated and recognized as the understood for their contribution to sexual products of different selective environments dimorphism. Persistent difficulties detecting and their respective potential to indicate these additional factors in the fossil record mating behaviour evaluated. means that these sources of variation often go unaccounted for. Although numerous References Cited different aspects of the dentition are Antón, Susan C., and Josh J. Snodgrass. dimorphic there is little agreement over the 2012. Origins and Evolution of Genus relative diagnostic value of each for Homo. Current Anthropology indicating mating systems. What is more, 53(6):479-496. because these different dimorphic characters are known to be the products of different Begun, David. 2004. The three “Cs” of selective processes they tend to produce behavioural reconstruction in fossil ambiguous and potentially contrasting primates. Journal of Human Evolution signals, the reasons for which are not always 46(4):497–505. apparent. An important prerequisite for studying sexual dimorphism is the reliable Berge, Christine, and Dionysis Goularas. differentiation of male and female 2010. A new reconstruction of Sts 14 morphology. Sex estimation in early pelvis (Australopithecus africanus) hominins, however, is rarely certain; from computed tomography and three- particularly when it is still unclear as to how dimensional modeling techniques. some specimens should be classified Journal of human evolution 58(3):262- taxonomically. Lastly, even in extant 272. species, recent scholarship shows that dental dimorphism exhibits only moderate to weak Berger, Lee R. 2012. Australopithecus correspondence with mating behaviour. sediba and the earliest origins of the genus Homo. Journal of More generally, the field of Anthropological Sciences 90:1-16. palaeoanthropology is persistently troubled by low sample sizes and fragmentary Bobe, Rene, and Anne K. Behrensmeyer. specimens, few of which are spatially and 2004. The expansion of grassland temporally relatable, and a generally poor ecosystems in Africa in relation to grasp of individual variation and taxonomic mammalian evolution and the origin of relationships. An improved knowledge of the genus Homo. Palaeogeography, hominin sexual dimorphism, as always, Palaeoclimatology, Palaeoecology could be improved by more fossil hominins 207(3):399-420. of identifiable sexes, from within a unified context. It is also crucial to comprehend how Conroy, G. C. 2005. Reconstructing Human alternate sources of variation such as diet, Origins. New York: W.W. Norton & substrate preference, female competition, Company, Inc.

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Harvey, Paul H., Michael Kavanagh, and T. Gingerich, Philip D. 1977. Correlation of H. Clutton‐Brock. 1978. Sexual tooth size and body size in living dimorphism in primate teeth. Journal hominoid primates, with a note on of Zoology 186(4):475-485. relative in Aegyptopithecus and Proconsul. American Journal of Häusler, Martin, and Peter Schmid. 1995. Physical Anthropology 47(3):395- Comparison of the pelves of Sts 14 398. and AL288-1: implications for birth and sexual dimorphism in Gingerich, Philip D., B. Holly Smith, and australopithecines. Journal of Human Karen Rosenberg. 1982. Allometric Evolution 29(4):363-383. scaling in the dentition of primates and prediction of body weight from tooth ———. 1997. Assessing the pelvis of AL size in fossils. American Journal of 288-1: a reply to Wood and Physical Anthropology 58(1):81-100. Quinney. Journal of Human Evolution 32(1):99-102. Gordon, Adam D., David J. Green, and Brian G. Richmond. 2008. Strong Hillson, Simon 1986. Teeth. England: postcranial size dimorphism in Cambridge University Press. Australopithecus afarensis: results from two new resampling methods for ———. 1996. Dental Anthropology. multivariate data sets with missing England: Cambridge University Press. data. American Journal of Physical Anthropology 135(3):311-328. Lockwood, Charles A., Brian G. Richmond, William L. Jungers, and William H. Grine, Frederick E., Gerhard W. Weber, J. Kimbel. 1996. Randomization Michael Plavcan, and Stefano Benazzi. procedures and sexual dimorphism in 2012. Sex at : 'Mrs. Ples' Australopithecus afarensis. Journal of is still an adult female. Journal of Human Evolution 31:537-548. Human Evolution 62(5):593-604. Kay, R. F., J. M. Plavcan, K. E. Glander, Grehan, John R. 2006. Mona Lisa smile: the and P. C. Wright. 1988. Sexual morphological enigma of human and selection and canine dimorphism in great ape evolution. The Anatomical New World monkeys. American Record Part B: The New Anatomist Journal of Physical Anthropology 289(4):139-157. 77(3): 385-397.

Gruter, Margaret. 1982. Biologically based Lande, Russell 1980. Sexual dimorphism, behavioural research and the facts of sexual selection, and adaptation in law. Journal of Social and Biological polygenic characters. Evolution Structures 5(4):315-323. 34(2):292-305.

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