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The concept of robusticity in (palaeo-) anthropology and its broad range of application: a short review

Le concept de robustesse en (paléo-) anthropologie et son large champ d’application : une courte revue
Tony Chevalier

Résumés

Le concept de robustesse est largement utilisé dans les études paléoanthropologiques et bioarchéologiques. Diverses structures squelettiques sont décrites comme robustes. De nombreuses personnes, à la fois des spécialistes et des non spécialistes, emploient le terme de robustesse oralement et familièrement pour souligner une impression générale, sans pour autant être conscients de tous les usages que recouvrent cette notion. Habituellement, la robustesse fait référence à l’état d’une structure osseuse, qui peut apparaître solide, costaude, épaisse ou renflée, et à sa capacité à résister à des charges. Une grande variété de critères, quantitatifs et qualitatifs, est choisie pour déterminer l’ampleur de la robustesse. Par exemple, certains auteurs évaluent l’hypertrophie, ou le renforcement, de l’os à partir d’une approche biomécanique, et normalisent les données révélant la résistance et la rigidité à partir des dimensions corporelles représentant la charge mécanique basique supportée par l’os ; d’autre auteurs se réfèrent à l’état des crêtes, des tori, et des rugosités. Parmi tous les usages, certains critères ne représentent rien de plus que la taille et la forme. En conséquence, le terme de robustesse (et son adjectif, robuste) doit être utilisé avec précaution, spécifiquement dans les synthèses et par les non-spécialistes.

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Introduction

1Robusticity is a well-known concept in human evolution studies and this term is very useful for expressing an impression of massiveness. The use of the term "robusticity" (but also "robustness" and the adjective "robust") is frequent in palaeoanthropological (or palaeontological) studies, but also in relation to various important biological issues such as: bone remodelling and vascularity and their relationship to bone robusticity (Miszkiewicz and Mahoney, 2019); relationships between physical activity, growth hormones and systemic robusticity (Lieberman, 1996; Copes et al., 2018); the relevance of mandibular robusticity (Daegling and Hylander, 1998), diaphyseal robusticity (Ruff et al., 2006) and the degree of robusticity of the human skull (Lahr and Wright, 1996; Curnoe, 2009; Baab et al., 2018) for biomechanical inferences; the similarity of factors at the origin of postcranial and cranial robusticity (Kennedy, 1985; Lieberman, 1996); and the influence of inheritance and growth on robusticity (Bridges, 2005).

2Historically, robusticity encompasses distinct meanings (including distinct kinds of anatomical traits and indices of robusticity) and this concept still has a broad range of application (Garralda et al., 2019; Belcastro et al., 2020; Richmond et al., 2020; Semaw et al., 2020). Robusticity is a familiar concept used by palaeoanthropologists to highlight specific ancient human traits: "The reduction of massiveness in the course of human evolution" (Weidenreich, 1943); "Neandertals and Pleistocene modern humans tend to be more robust than Holocene humans" (Weaver, 2009). Etymologically, the word means a strong or heavy structure, such as, for example, a strongly built skull, and refers to the ability of a bone structure to resist loads. It thus refers to both a mechanical aptitude and a build-up of bone in places. It is generally easy to understand what an author means by skeletal robusticity in the context of a specific study. Paradoxically, however, if we consider studies in general, the definition seems to be too broad and too variable to bear any real meaning. The definitions used in such studies include references to shape, size or thickness (scaled or unscaled), strength (biomechanically quantified or hypothetical) and additional bone mass. Consequently, skeletal robusticity cannot be used without proper contextualization.

3Given that the robusticity of prehistoric humans is strongly rooted in our minds, it is possible that we are less inclined to criticize the use of the term and more inclined to give the term the meaning we choose and thus perpetuate certain habits. Robusticity is described, quantified and discussed by palaeoanthropologists, included in synoptic overviews by prehistorians and anchored in the field of knowledge of students and the general public. But does it make sense to state that prehistoric humans are robust? Specialists would probably agree to say "no", because it is essential to say how robust they are and to state how this has been measured. The general meaning of robusticity needs to be differentiated from its specific definitions or applications. Some authors have, for a long time, explicitly or implicitly pointed out the weaknesses of the definition of robusticity and found it pertinent to define it in the context of their studies (Henri-Martin, 1913; Piquet, 1956; Ruff et al., 1993; Churchill, 1998; Pearson, 2000; Foster et al., 2014; Ruff, 2018). The concept of robusticity applies to distinct biological tissues (tooth and bone), structure (cortical and trabecular; exo- and endo-structure) and anatomical regions (distinct bones, diaphyses and articular parts). The skull, mandible, pelvis, appendicular bones, teeth (crown and roots) and entheses have long been associated with the term robust. The different practices stem from the overall definition of robusticity and various components of the human skeleton studied. Although these practices are often justified, in some instances, they can lead to inconsistencies and raise questions.

4The purpose of this paper is to point out, in the form of a short review, the wide range of contexts in which the concept of robusticity is used, and its distinct use in specific fields of study. Furthermore, I underscore misuses that may generate ambiguity, and recommend when it is best not to refer to robusticity. Such an exercise cannot claim to be exhaustive (also for references), but should provide enough information to raise awareness. Defining a structure as robust is only meaningful when it is properly contextualized. Although contextualization seems an obvious requirement in science, the varied use of this term in different specialities in anthropology, and its use in syntheses and by non-anthropologists, require a clear definition and the identification of inappropriate uses. In the light of these points, this review is intended for a wide audience.

5We first present the various uses of the term "robusticity". They refer to specific definitions related to distinct skeletal structures and regions. Secondly, we compare practices concerning some classic variables and distinct structures. Thirdly, we point out some of the confusion surrounding the use of the term robusticity and the difficulties that arise in restricting its range of application.

Definitions of robusticity designed for distinct structures

6These specific definitions of robusticity used in biological anthropology show the wide variety of robusticity criteria, misuse or subjective criteria, habits and sometimes debates surrounding robusticity. Figures 1-6 illustrate the disparate nature of robusticity criteria with some examples from a non-exhaustive overview.

Cranium: superstructure and thickness

7Cranial robusticity refers to size, shape and the presence/absence of distinct morphological features (figure 1), frequently grouped under the term superstructure (Weidenreich, 1939; Lahr and Wright, 1996; Lieberman, 1996; Baab et al., 2010). Crests, tori, ridges, processes, rugosities, dimensions and even the degree of rounding of a margin can be used to determine the degree of robusticity in cranial analysis (Weidenreich, 1939; Lahr and Wright, 1996; Lieberman, 1996; Baab et al., 2010). Skull robusticity is classically expressed by the existence of large cranial superstructures. The presence of brow ridges, occipital tori and thick vault bones denotes a robustly or strongly built skull. The term robust describes something "strongly formed or constructed" (Lahr and Wright, 1996), "well-developed/strongly expressed cranial superstructures and elevated cranial thickness" (Baab et al., 2018) or "heavily-built, well-defined, rugged or corpulent" traits (Curnoe, 2009). The "standardization" of non-metric features (Lahr, 1994) expressed by grade and scoring technique are applied to the skull to make comparative analyses more objective (Lahr, 1992; 1994; 1996). This "standardization" is different from the standardization applied to long bone strength to measure diaphyseal robusticity (e.g., Ruff, 2018). Lahr and Wright (1996) note that cranial robusticity included more types of features than postcranial descriptions. Functional investigations of the skull have been conducted and discussed for some time (Washburn, 1947; Endo, 1966; Russell, 1985; Hylander et al., 1991; Kitai et al., 2002; Fiscella and Smith, 2006; Curnoe, 2009; Menegaz et al., 2010). However, bioanthropologists do not quantify skull robusticity with strength measurements and standardization as is common in postcranial biomechanical studies. This is due to the complexity of biomechanical investigations of the cranium (unlike a long bone cross-section for example). The relevance of standardizing the cranium with body mass is not proven and it is difficult to assess body mass from an isolated cranium. Ultimately, applying a biomechanical approach to quantify skull structures in the same way as postcranial bones is challenging: to assess the degree of robusticity, cranial superstructures are not scaled to body size (as the bone is not weight-bearing) or standardized to any relevant mechanical size. Generally, only the absolute degree of expression or development of skull traits is required (Lahr and Wright, 1996; Baab et al., 2010).

8Accordingly, cranial robusticity refers to a compilation of different types of features described in terms of shape and size without scaling. The description of cranial robusticity is a special case compared to other skeletal structures. Note that these very disparate characteristics are from distinct skull bones with highly variable vault thicknesses (Balzeau, 2013) and are part of a complex functional pattern (van der Klaauw, 1952; Moss and Young, 1960).

Figure 1

Figure 1

Some non-metric and metric criteria of cranial robusticity. The supraorbital torus of Neandertal (A, blue arrow) is classic evidence of robusticity differentiating Neandertal from Homo sapiens (B). Cranial robusticity is based on very diverse non-metric criteria such as rounding, degree of development, absence/presence and depth: (1) degree of sagittal keeling, (2) development of the supraorbital ridges and formation of a supraorbital torus, (3) depth of the infraglabellar notch, (4) categories of the nasal saddle, (5) rounding of the infero-lateral margin of the orbit, (6) development of the zygomatic trigone, (7) absence or presence of a tubercle on the lateral surface of the mastoid process. Cranial thickness (C), as a variable of robusticity, is often used without scaling |
Quelques critères non-métriques et un critère métrique liés à la robustesse crânienne. Le torus supraorbital des Néandertaliens est un témoin classique de robustesse qui permet de les différencier des Homo sapiens (B). La robustesse crânienne est basée sur diverses caractéristiques non-métriques dont l’arrondissement, le degré de développement, l’absence et la présence, ainsi que la profondeur : (1) degré de développement de la carène sagittale ; (2) développement des crêtes supra-orbitaires et la formation du torus supraorbitaire ; (3) profondeur de l’échancrure infra-glabellaire, (4) catégories des os nasaux, (5) arrondissement du bord inféro-latéral de l’orbite, (6) développement du trigone du zygomatique, (7) absence/présence du tubercule sur la surface latérale du processus mastoïdien. L’épaisseur crânienne (C), utilisée comme un critère de robustesse, n’est généralement pas rapportée à une autre dimension

Mandible: relative size and shape

9Boule (1912) created the term "index of robusticity" when describing the Chapelle-aux-Saints mandible and defined it as corpus breadth over height. This terminology appeared long after Topinard (1886) and Filhol (1889) used this index when studying the Neandertals of La Naulette and Malarnaud, respectively. Henri-Martin (1913) specified the limits of the robusticity index and used the perimeters at different locations. Piquet (1956) proposed a profile of robusticity from successive perimeters of the mandible corpus from the symphysis to the third molar to highlight a spatial representation of massiveness and to select a more significant method to discriminate between human groups. Thus, the meaning of the robusticity index has ranged from a description of shape (shape criterion based on breadth over height) to a representation of one or more dimensions (size criterion based on perimeters). Many years after these studies, the robusticity index is still frequently defined as the ratio of corpus breadth to height, or thickness to depth, and is used in many human fossil studies for taxonomic purposes (Chamberlain and Wood, 1985; Rosas and Bermúdez de Castro, 1999; Carbonell et al., 2005), although not everyone links this formula to robusticity (Ballolia et al., 2020) and other indices have been incorporated into studies (figure 2). Daegling (1989) noted the inaptitude of the traditional index of "robusticity" to give real information about the robusticity of the mandibular corpus. He considers this index as a shape index differing from the usual meaning given to long bone robusticity with diaphyseal dimensions divided by bone length, and concluded: "Mandibular length, by approximating the moment arms of the forces acting on the corpus, provides a mechanically relevant denominator for any index of mandibular robusticity". It seems more suitable to divide or regress the cross-sectional moment of inertia and the diameter of the section by mandibular length (Hylander, 1979; 1988). Interestingly, Daegling et al. (2016) measure the polar moment of inertia (J, torsional and average bending rigidity), and K (an analog to the section modulus, torsional strength), relative to mandibular length (J0.25/ML; K0.33/ML), but only use the measurements and mechanical interpretations, and not the term "robusticity". Until recent publications, Daegling and collaborators (Daegling and Grine, 2017) kept the term "robusticity" for an index they knew to be a shape index, which paradoxically avoids confusion with the classical mandibular index but maintains confusion over its mechanical meaning. Other measures (Brown and Maeda, 2009) and qualitative traits of robusticity based on muscular skeletal markers (figure 2) are also sources of misperception since they do not convey biomechanical meanings with respect to the biomechanical method of Hylander (1979; 1988), Daegling (1989) and Daegling et al. (2016). In the same way as for the cranium, mandibular robusticity can also be defined from bone superstructure (figure 2). Morphological prominence and groove traits are used to define robusticity. For example, Mounier et al. (2009) highlight robusticity of the Mauer mandible on the basis of the presence of the sulcus intertoralis, lateral prominence and the wide extra-molar sulcus. Conversely, moderate development of alveolar prominence is evidence of gracility (Wu et al., 2017).

Figure 2

Figure 2

Some metric and non-metric criteria of mandibular robusticity. Mandibular robusticity is usually quantified from coronal cross-sections and described from various non-metric traits, as mentioned in figure 2. Ix: second moment of area about buccolingual axis (superoinferior bending rigidity); Iy: second moment of area about superoinferior axis (buccolingual bending rigidity); K: Bredt’s formula for thin-walled sections (torsional strength); ML: mandibular length; CA: cortical area |
Quelques critères métriques et non-métriques liés à la robustesse mandibulaire. La robustesse des mandibules est habituellement quantifiée à partir de sections coronales de la branche horizontale et décrites par divers traits non-métriques, comme indiqué sur la figure 2. Ix : second moment d’aire selon l’axe bucco-lingual (rigidité à la flexion dans le plan supéro-inférieur) ; Iy : second moment d’aire selon l’axe supéro-inférieur (rigidité à la flexion dans le plan bucco-lingual) ; K : formule de Bredt pour les sections à fine paroi (résistance à la torsion) ; ML : longueur mandibulaire ; CA : aire corticale

Tooth and root

10Skeletal robusticity is also applied to teeth in the description of crowns and roots (figure 3). Classic crown robusticity, or the robusticity module, corresponds to the product of the mesiodistal by the buccolingual diameter (Martin and Saller, 1957), while such an index represents an approximate area of a crown section. Several terminologies agree with the latter meaning: cross-sectional area (Brace and Mahler, 1971), occlusal area (Hillson et al., 2005) and tooth area (Rougier et al., 2017). Recently, Garralda et al. (2019) referred to crown and cervical robusticity using a quantitative description, extending the classic use of crown robusticity (Lumley, 1987; Mallegni, 1995; Condemi, 2004; Becam and Chevalier, 2019). It should be noted that many studies of human tooth evolution no longer mention the robusticity index (or area index) and only analyze raw diameters.

Figure 3

Figure 3

Some metric and non-metric criteria of tooth robusticity. A- Metric "crown" robusticity is based on crown and cervical diameters. B- Non-metric crown robusticity is based on discrete traits: the second molar B1 is more robust than B2 considering additive traits. C- Metric root robusticity is based on diameter and root length. D- Root robusticity is often estimated visually; given that large and bulging roots are usually accepted as evidence of robusticity, root D1 presents a more robust morphology than D2. MD: mesiodistal diameter; BL: buccolingual diameter |
Quelques critères métriques et non-métriques liés à la robustesse des dents. A- La mesure de la robustesse de la couronne prend en compte les diamètres coronaires et cervicaux. B- La robustesse coronale non-métrique est établie à partir des traits discrets : la seconde molaire B1 est plus robuste que la seconde molaire B2 en raison de la cumulation des traits. C- La mesure de la robustesse racinaire peut se calculer en rapportant le diamètre de la racine à sa longueur. D- La robustesse de la racine est souvent évaluée visuellement ; étant donné que des racines larges et bombées sont généralement acceptées comme une preuve de robustesse, la racine D1 présente une robustesse plus élevée que la racine D2

11The presence/absence and degree of expression of crown morphological traits (e.g., shovel shape, accessory cusp, crest, tuberculum) can also characterize robusticity. High frequencies of "massive additive traits" (figure 3) correspond to high robusticity or "morphological robusticity" (Martinón-Torres et al., 2007). However, such references to robusticity are not the rule (Martinón-Torres et al., 2012; Bailey et al., 2017).

12To my knowledge, the term "robusticity" is not employed for tooth microstructure. High average enamel thickness (AET) and relative enamel thickness (RET), which represent both the "relative" thickness of enamel from a section (2D) or volume (3D), are not reported as an increase in robusticity (e.g., Shellis et al., 1998; Olejniczak et al., 2008a,b; Smith et al., 2012; Skinner et al., 2015; Martín-Francés et al., 2020; García-Campos et al., 2021).

13Roots have sometimes been described as "robust" without clear explanations about how the dimensions and morphological characteristics of the root affect the determination of a "robust" root (Wu and Poirier, 1995; Garralda et al., 2019). "Pillar-like" (Pan et al., 2019) or "column-like" (Xing et al., 2018) characteristics may serve to define a "robust" root, as well as its rounded and large apex, which reflect its overall robust appearance (figure 3). Another approach consists of a traditional quantification of robusticity applied to the diaphysis, with root diameter divided by root length (Wood et al., 1988).

Diaphysis and cortical bone

14Diaphyseal robusticity including cortical bone can be determined in several ways at multiple locations (figures 4-5). Any region of the epiphysis, metaphysis and diaphysis can be assessed for robusticity in multiple ways. The quantification of long bone diaphyseal robusticity has been thoroughly investigated from methodological and functional perspectives for many years (Ruff et al., 1993; Trinkaus and Ruff, 2000; Shaw and Stock, 2009a, b; Carlson and Marchi, 2014; Ruff et al., 2015; Ruff, 2018; Holt and Whittey, 2019). Currently, biomechanical measurement of diaphyseal robusticity is often based on cross-sectional geometric properties (CSG) (see CSG definitions in Ruff (2008)), but the external diameter can also be used (Stock and Shaw, 2007). CSG include the external and cortical dimensions of diaphyseal cross-sections (Runestad et al., 1993). This biomechanical method models long bones in the same way as an engineering beam to evaluate mechanical properties (Lovejoy et al., 1976; Huiskes, 1982; Ruff and Hayes, 1983; Ruff, 1989; Gere and Timoshenko, 1990). Robusticity is defined as the "strength or rigidity of a structure relative to the mechanically relevant measure of body size" (Ruff et al., 1993) or, in other words, "the amount of structural material (bone tissue) for a given structure relative to the overall size (mass or length) of the organism, and hence the amount of structural reinforcement scaled to the size of the organism. It is not merely size, a confusion sometimes present in the paleoanthropological literature" (Trinkaus et al., 1991). Usually, biomechanical diaphyseal robusticity is measured from the polar moment of area (J), an approximation of torsional and average bending rigidity, or from the polar section modulus (Zp), an approximation of torsional and average bending strength. These variables are standardized with bone length (BL) and body mass (BM) (Ruff et al., 1993; Trinkaus, 1997; Ruff, 2018). Biomechanical diaphyseal robusticity can also be measured from a cross-section along a specific axis. For example, robusticity can be measured with the following formula: Ix/(BL2*BM). The second moment of area about the mediolateral axis (Ix) represents bone rigidity in the anteroposterior plane.

Figure 4

Figure 4

Some metric criteria of postcranial robusticity. Many robusticity indices can be measured from one bone. Some measurements represent size or relative size, without appropriate scaling for a biomechanical approach. Robusticity can be quantified at any location on the diaphysis. a AP standardized bending rigidity; b AP standardized bending strength; c standardized torsional rigidity. DAP: anteroposterior diameter; DML: mediolateral diameter; std: standardized; Ix: second moment of area about mediolateral axis (anteroposterior bending rigidity); Zx: section modulus about mediolateral axis (anteroposterior bending strength); J: polar second moment of area (torsional and twice average bending rigidity) |
Quelques critères métriques liés à la robustesse du squelette post-crânien. De nombreux indices de robustesse peuvent être mesurés à partir d’un seul os. Certaines mesures ne représentent que la taille ou la taille relative, et ne sont pas correctement standardisées pour une approche biomécanique. Notons que la robustesse peut être quantifiée à n’importe quel niveau sur la diaphyse. a La rigidité à la flexion selon le plan AP, standardisée ; b La résistance à la flexion selon le plan AP, standardisée ;  c La rigidité à la torsion, standardisée. DAP : diamètre antéro-postérieur ; DML : diamètre médio-latéral ; std : standardisé ; Ix : second moment d’aire selon l’axe médio-latéral (rigidité dans le plan antéro-postérieur) ; Zx : Module de section selon l’axe médio-latéral (résistance à la flexion dans le plan antéro-postérieur) ; J : second moment d’aire polaire (rigidité à la torsion et rigidité moyenne à la flexion)

Figure 5

Figure 5

Some non-metric criteria of postcranial robusticity. The means used to visually assess the degree of bone robusticity are very diverse, subjective and strongly dependent on the observer and his/her conception of robusticity. A quantitative (i.e., biomechanical) method could give distinct results considering the cross-sectional geometric properties of diaphysis, bone length and body mass. A- According to the enthesis scoring method, the Neandertal A2 is more robust than the Upper Palaeolithic modern human A1. B- For many anthropologists, the immature humerus B2 is more robust than humerus B1, given the periosteal diameter/bone length ratio. C- Given its cortical reinforcement, the fibular diaphysis C1 could be considered as more robust than C2. Red represents maximum cortical thickness on the map |
Quelques critères non-métriques liés à la robustesse du squelette postcrânien. Les évaluations visuelles du degré de robustesse des os sont très diverses, subjectives et dépendent fortement de l’observateur et de sa conception de la robustesse. Une méthode quantitative (c.-à-d., biomécanique) pourrait donner des résultats distincts en tenant compte des propriétés géométriques de la section transversale de la diaphyse, de la longueur des os et de la masse corporelle. A- Selon la méthode de cotation des enthèses, le Néandertalien A2 est plus robuste que l’Homme moderne du Paléolithique supérieur A1. B- Pour de nombreux anthropologues, l’humérus immature B2 est plus robuste que l’humérus B1 compte tenu du rapport entre le diamètre de la section et la longueur de l’os. C- Étant donné le renforcement cortical de la diaphyse fibulaire C1, elle peut être considérée comme plus robuste que la diaphyse C2. La couleur rouge représente l’épaisseur corticale maximale sur la cartographie

15"Biomechanical" diaphyseal robusticity distinguishes "traditional" or "classic" diaphyseal robusticity based on external diameters/circumference divided by bone length, a linear measure of overall size (Martin and Saller, 1957; Trinkaus, 1976; Bräuer, 1988; Pearson, 2000). Pearson (2000), contrary to Trinkaus and Ruff (2000), argues that these two measures of robusticity (mechanical versus traditional) belong to two distinct approaches. Pearson (2000) suggests that the biomechanical method of Trinkaus, Ruff and colleagues should refer to a term such as "residual strength" and not to "robusticity". Thus, the definition of robusticity should retain the traditional index (e.g., diameter/bone length). According to Trinkaus and Ruff (2000), biomechanical and traditional robusticity are part of the same approach but the method has changed by improving its ability to scale bone structure.

16The amount of cortical area (CA) is also a classic way of expressing robusticity in past populations. Changes occurring during human evolution suggest a decrease in robusticity/hypertrophy (Kennedy, 1983; Ruff et al., 1993; Churchill, 1998; Trinkaus and Ruff, 2012). Cross-sectional CA (or cortical width) relative to total area (TA) (or external diameter, circumference), and relative to BM (or BL) can represent two distinct indices of "robusticity", while it is highly recommended to standardize CA by BM for biomechanical purposes (Kennedy, 1983; Ruff et al., 1993; Ruff, 2000; 2008; Miszkiewicz and Mahoney, 2019). We consider that CA specifically resists pure axial loading while diaphyses are rarely subject to pure tension or compression during bipedalism (Ruff, 2000; 2008). Both indices of robusticity provide information about the reinforcement of the diaphysis, but the former (CA/TA) refers to additional bone mass relative to the size of a cross-section and the latter (CA/BM) to the amount of structural material relative to body size.

Trabecular bone

17Bone fraction (BV/TV), sometimes used as a measure of robusticity, is a key variable in human evolutionary hypotheses (Chirchir et al., 2015; Ryan and Shaw, 2015) and ontogenetic perspectives (Ryan and Krovitz, 2006; Reissis and Abel, 2012; Colombo, 2014; Acquaah et al., 2015; Milovanovic et al., 2017; Ryan et al., 2017; Saers et al., 2019a; Chevalier et al., 2021). BV/TV measures the amount of trabecular bone (BV: bone volume) contained within a region of interest (TV: total volume) and depends on other variables such as trabecular thickness and number (Dempster et al., 2013; Chevalier et al., 2021). It is generally analyzed in the metaphysis for immature individuals and in the epiphysis for adult individuals (figure 4). However, some anthropological studies refer to bone density, as synonymous with bone fraction (Chirchir et al., 2015; 2017), using the physical sense (i.e., the mass of a body divided by its volume) (Odgaard and Gundersen, 1993; Land and Schoenau, 2008), which differs from clinical practices referring to bone attenuation against a beam of radiation, better named bone mineral density (Cameron and Sorenson, 1963). By an unfortunate inference, bone (mineral) density could mean bone fraction and would then become a measure of robusticity (see in Best et al., 2017). In practice, BV/TV, trabecular thickness and volumetric bone (mineral) density are sometimes considered as an indicator of robusticity, or of its opposite, gracility (Lazenby et al., 2011; Chirchir et al., 2015; 2017; Ryan and Shaw, 2015; Best et al., 2017; Colombo et al., 2019; Saers et al., 2019b). Note that Ryan and Shaw (2015) used a mass-corrected trabecular bone fraction to evaluate robusticity/gracility. They determined the relationship between BV/TV and body mass in non-human primates and defined recent low-mobility humans as gracile, since their BV/TV is lower than the expected BV/TV.

18Therefore, the concept of robusticity is related to several trabecular bone variables but the use of BV/TV as an indicator of robusticity is not the rule. It is interesting to note the lack of the use of the term robusticity in Doershuk et al. (2019), except in the abstract, where it is practical for summarizing the main conclusion. Finally, as discussed further below, TV do not represent an appropriate approximation of the baseline load (or body size). Thus, BV/TV is not an equivalent of the biomechanical robusticity measured from the diaphyseal cross-section.

Postcranial entheses

19Tendons, ligaments and joint capsules are attached to bone in a region called the enthesis (Benjamin et al., 2002), which varies in surface complexity, shape and size (Foster et al., 2014). Some enthesis studies refer to the robusticity of enthesis or musculoskeletal massiveness as a modification of the entheseal surface (Trinkaus et al., 1991; Hawkey and Merbs, 1995; Mariotti et al., 2007; Foster et al., 2014; Belcastro et al., 2020), and distinguish robusticity, a normal adaptation, from enthesopathy (Foster et al., 2014). According to Mariotti et al. (2007), entheseal robusticity represents "the physiological bone response to the muscle or ligament solicitations". The overall morphology described by size, crest, groove, irregularity and number of reliefs of attachment sites has sometimes been summarized using the single term robusticity (figure 5). To summarize, for many authors, any morphology deviating to some degree from a smooth, flat and regularly curved surface would be robust (figure 6). Scoring the degree of development of "robusticity" reduces subjectivity (Mariotti et al., 2007), but the score and degree are themselves subjective and intra- /inter-observer errors are significant. Results ultimately depend on users’ practices. Many studies do not need the term robusticity to frame their hypotheses or report their results (Zumwalt, 2005; Acosta et al., 2017; Wallace et al., 2017; Karakostis et al., 2019; Nikita et al., 2019; Djukić et al., 2020), even when entheseal sizes are scaled with bone size or body size (Karakostis et al., 2019). Complexity can summarize some of the "robust" features. The term complexity is already in use and can be described qualitatively and quantitatively (Zumwalt, 2005; Wallace et al., 2017).

Figure 6

Figure 6

Surface changes and "morphological robusticity". If we attempt a synthesis of the different practices by visually assessing robusticity, gracility would be a neutral structure (smooth, flat, regularly curved, see A). Any additional material, or less material by sculpting the surface, could be evidence of robusticity. According to this definition of robusticity, structures B and C are more robust than A; D is more robust than A, B and C |
Modifications de surface et "robustesse morphologique". Si l’on tente une synthèse des différentes pratiques d’évaluation visuelle de la robustesse, la gracilité serait représentée par une structure neutre (lisse, plate, régulièrement courbée, voir A). Tout apport de matière, ou toute suppression de matière sculptant la surface, pourrait être utilisé comme une preuve de robustesse. Selon cette perception de la robustesse, les structures B et C sont plus robustes que A ; D est plus robuste que A, B et C

Epiphyses

20Epiphyseal or articular robusticity was traditionally calculated by dividing the size of an articular region by bone length (Ruff et al., 1993; Pearson, 2000). The size of the articular surface (e.g., head diameter) or the overall size of the epiphysis (e.g., biepicondylar breadth) can be used to measure indices of robusticity (figure 4). Such an index can simply be named articular index, whereas robusticity index can be restricted to diaphyseal robusticity (Trinkaus, 1980). However, the nomenclature used by authors is not always consistent. Trinkaus et al. (1991) include the term articular robusticity for the glenoid surface of the scapula. They also use articular hypertrophy to express the relative size of an articular surface. The meaning of robusticity appears particularly confusing in some instances. For example, Churchill (1998) introduces the term relative articular robusticity for a discussion about Neandertals and their adaptation to the cold. However, no analysis of articular robusticity was performed. While this terminology is not habitual, it is unclear, since traditionally an index of articular robusticity is relative by nature. In this example, it seems that large size means high robusticity. Currently, relative articular size (i.e., size scaling by bone length) is rarely used as an index of robusticity (but see Pearson, 2000). A well-defined robusticity index would require adjusting lower limb articular size at least to body mass, but this would be a tautological approach since usually articular size is used to estimate body mass.

Quantitative variables and robusticity: thickness, relative amount of bone and shape

21Here, our concern is to compare practices between distinct contexts (different structures or regions of the skeleton) based on classic types of variables. We are talking about tissue thickness in the skull, teeth and long bones, the amount of cortical and trabecular bone in a region of interest, and the shape of the mandibular corpus and long bone cross-section. Some types of quantitative variables related to the concept of robusticity seem inappropriate or at least questionable. We will see that practices differ according to the structures studied.

22An increase in cranial vault, enamel and cortical thicknesses does not indicate an increase in robusticity, but merely an increase in size. However, Baab et al. (2018) include cranial vault thickness in their criteria of robusticity. Cranial vault thickness cannot measure robusticity without appropriate scaling; it represents size in the same way as diaphyseal cortical and enamel thicknesses. It seems that this misinterpretation of robusticity does not occur in diaphyseal and tooth studies. It is interesting to note that the relative thickness of tooth enamel is not used as an index of robusticity. Robusticity is often related to functional interpretation and biomechanical approaches that require the scaling of variables. However, high average enamel thickness (AET) and relative enamel thickness (RET) are not stated as an increase in robusticity, as previously mentioned, even if enamel thickness in primates is often used to evaluate the capacity of teeth to resist fractures or to prevent dental wear (e.g., Molnar and Gantt, 1977; Vogel et al., 2008; Lee et al., 2010; McGraw et al., 2012; Pampush et al., 2013). When Schwartz et al. (2020) suggest that absolute crown strength is a better assessment of tooth strength than relative enamel thickness (RET), again they do not refer to "robusticity".

23The relative amount of trabecular and cortical bone is quantified with bone fraction (BV/TV) and relative cortical area (CA/TA), and sometimes used as evidence of robusticity (e.g., Kennedy, 1983). These indices are mathematically and geometrically close, but BV/TV is of great interest for functional investigations, in contrast to CA/TA (Ruff et al., 1993; Trinkaus and Ruff, 2012; Ryan and Shaw, 2015). In fact, neither BV/TV nor CA/TA is a good measurement of biomechanical robusticity because neither TV nor CA reflects appropriate scaling (i.e., body size). In other words, TA and TV cannot scale bone strength since they measure neither the baseline load nor the moment arm. However, clarification is required for these indices given the varying accepted applications of robusticity. The variation of an index as the result of the variation in mechanical loads (i.e., variation in bone strength, rigidity) could be accepted as an index of robusticity. First, TV is used to scale BV, even though it is not biomechanically appropriate, and BV/TV frequently increases when stresses increase (see the review by Kivell, 2016). Thus, BV/TV reflects the ability of trabecular bone to adapt and resist to loads. This index is not clearly differentiated from the general (and not strictly biomechanical) definition of robusticity. Although it does not seem advisable to associate an increase in BV/TV with an increase in robusticity, it seems difficult to radically oppose this practice. Nevertheless, if authors compare distinct primate genera, the inappropriate use of BV/TV is more substantial. Overall joint size (i.e., TV) depends not only on reaction joint force (i.e., joint loading) but also on joint excursion. Thus, variation in BV/TV is not only due to variation in BV but also to variation in TV (which does not only reflect joint loading). Since body plan and locomotion are distinct in primates, TV is not an analogous variable. If some authors wish to use BV/TV as a robusticity index, then it is advisable to use it in studies including closely related species. Interestingly, Ryan and Shaw (2015) showed the relationship between the BV/TV and body mass in primates. They suggested a recent decrease in human robusticity (i.e., gracilization) based on the expected BV/TV: the BV/TV of recent humans is lower than expected given body mass. Their method is more appropriate for a biomechanical perspective. Secondly, in the same away as BV, CA is scaled, and CA/TA can then potentially be used as a robusticity index. However, variation in CA/TA does not necessarily reflect variation in strength. A higher CA/TA (i.e., potentially an increase in robusticity) can be the result of an increase in CA or a decrease in TA. In the latter case, relative bone strength could decrease dramatically (i.e., robusticity decreases), while CA/TA increases, since a larger cross-section provides a strength benefit for the same cortical area, i.e., moment of inertia and section modulus increase (van der Meulen et al., 2001). For the same TA of a circular section, an increase of 80% in CA only produces an increase of 25% for the moment of inertia and the section modulus; while for the same CA, a decrease of 25% in TA (i.e., an increase of CA/TA) produces a dramatic decrease of 62% and 48% of the moment of inertia and section modulus, respectively (van der Meulen et al., 2001). The results of the biomechanical analyses therefore oppose the use of CA/TA as an index of robusticity based on the functional conception. The recommended biomechanical robusticity index, when including CA, is CA/BM (Ruff, 2000).

24The mandibular robusticity index (Boule, 1912) is mathematically similar to classic long bones indices such as the pilastric index (Hepburn, 1896). It provides information about "shape" or the lengthening of a section. The increase in the mandibular transversal diameter could be understood as a transversal reinforcement of a preliminary more oval section and interpreted as an increase in robusticity. A rounded section of the mandibular corpus is an optimal section for countering torsion, i.e., resisting twisting moments, because stresses are evenly distributed on the outer surface of the bone section (Hylander, 1979; Daegling and Grine, 2007). A rounded section represents an index of "robusticity" of 1, whereas human mandibles are generally oval and have indices well below 1, indicating a predominance of height over breadth (Chamberlain and Wood, 1985). However, this reinforcement is only relative to another measure of the same section, and not to a mechanically relevant size. Contrary to certain practices when analyzing mandibles, such indices in long bones are not associated with robusticity. Clearly an increase in the ratio between the anteroposterior diameter and the mediolateral diameter (DAP/DML), or the ratio of the second moment of areas (Ix/Iy) in cross-sectional long bone reflects shape (Trinkaus and Ruff, 2012). A relatively more antero-posteriorly strengthened diaphyseal cross-section may reflect a decrease in mediolateral diameter or anteroposterior strengthening. Measures of diaphyseal robusticity need to scale the anterior reinforcement to the bone length times the body mass (or at least to bone length). The shape index (e.g., DAP/DML; Ix/Iy) could be used as a proxy for anteroposterior robusticity in some instances, but this requires calculating robusticity first, with a good index of robusticity, to be sure. In biomechanical perspectives, shape and robusticity measures convey distinct meanings and are used to investigate two kinds of objectives; one reflecting the pattern of activity (shape), the other its level (robusticity) (Trinkaus et al., 1991).

Topography and robusticity

25Surface variations are analyzed for teeth and bones. The scoring method is used to reduce subjectivity, but it is not the rule. Some of these variations are also quantified. Here, the use of the term robusticity in entheses and tooth occlusal surface studies are briefly compared. The surface of entheses and the occlusal surface of teeth (considering the crown or the enamel-dentine junction) sometimes present topographic similarities with a bone surface crossed by ridges and depressions. The reinforcement of these distinct structures by additional biological material can be interpreted as the ability of the structure to resist loads, and they can relate to adaptation (genetic or during life) to specific activities, although teeth and bone present distinct tissues, development and functional relationships. Beyond the recurrent qualitative analysis of the discrete characteristics and complexity of teeth (Bailey, 2002), the complexity and crenulation of the occlusal tooth surface can be assessed by 3D topographical quantification (Guy et al., 2013; Berthaume et al., 2020). Similarly, entheseal complexity can also be described qualitatively and quantitatively (Zumwalt, 2005; Wallace et al., 2017). Surface relief and surface curvature can complete the description of the surface complexity of an enthesis in a morphological topographic analysis (Wallace et al., 2017), as in tooth studies (Winchester et al., 2014). However, robusticity is rarely used to define tooth grooves, ridges, and discrete features (but see Martinón-Torres et al., 2007), in contrast with some practices in enthesis studies (Trinkaus et al., 1991; Hawkey and Merbs, 1995; Mariotti et al., 2007; Foster et al., 2014; Belcastro et al., 2020).

Some examples of confusion

26The purpose of this review of definitions and practices is to avoid confusion and make the reading of anthropological studies clearer. Here, I present three examples from Wu and Poirier (1995), Di Vincenzo et al. (2015) and Saers et al. (2019b), which cannot be considered generalized practice but which highlight the confusion that can emerge from the variable use of the concept of robusticity. It is not a question of pointing out the errors of these authors but the complexity of uses that the concept of robusticity can encompass.

27In their studies of human evolution in China, Wu and Poirier (1995) described tooth morphology. Like many other authors in oral or written communication, they employed terms such as robust and strong to express the appearance of the morphology of human remains. This results in doubts about the meaning of the terms. For example, if "strong" means "robust", then what can "the incisor crowns are strong and robust" (Wu and Poirier, 1995) mean? In such a context, what is the general term for "well-developed basal tubercle", "abundant ridges" and "marked shovel-shape", for example? Do they refer to a strong or robust crown?

28Di Vincenzo et al. (2015) make a link between the robusticity of the adult humerus of Gombore I and that of the immature mandible of Garba (Condemi, 2004). However, evidence of robusticity is based on the cortical area relative to total area (CA/TA) of the diaphyseal cross-section for the former (Di Vincenzo et al., 2015) and an index of shape for the latter (Condemi, 2004). This search for coherence and a summarized view may give rise to the postulate that the humans of Melka Kunture are robust. However, this is meaningless since the two studies use distinct meanings of robusticity. Furthermore, the two indices are not appropriate as indices of robusticity with a more restricted (and better) definition of robusticity (see above).

29Saers et al. (2019b) present another somewhat more subtle and perhaps less inconvenient example of unfortunate association. Saers et al. (2019b) evoke the significant decrease of robusticity during human evolution. This occurs with the adoption of agriculture and has been highlighted in trabecular (Chirchir et al., 2015; 2017) and cortical bone (Macintosh et al., 2014; Ruff et al., 2015). However, indices of robusticity calculated from these two bone structures correspond to two distinct definitions although the two bone structures are modulated by physical behaviour. Diaphyseal cortical robusticity is relative to the baseline load (i.e., body size). In contrast, the bone fraction of the trabecular bone (only) measures the relative amount of trabecular bone in a region of interest (BV/TV). TV does not approximate the baseline load since it is not adjusted to body size.

Towards homogenization of the use of the robusticity concept: a difficult goal to achieve

30Skeletal robusticity is bone-, bone region-, axis-, and structure-dependent. Inevitably, a very large number of robusticity indices can be calculated for the same bone, based on the same concept and method. Thus, one femur can be robust distally to the lesser trochanter and gracile at mid-diaphysis (figure 4). Several types of unavoidable dualism occur through studies (e.g., old versus new approaches, subjective versus objective observations, quantitative versus qualitative data, scaling size versus size versus shape, biomechanical versus taxonomical interest, region-specific versus overall bone robusticity). Given the various applications of the concept of robusticity, it seems important to define what can be improved to clarify the issue and avoid endless extensions of its application.

31The overall conception of cranial, tooth and enthesis robusticity refers to what should be robust a priori. There is no specific definition of this "morphological robusticity", just an inconsistent list of diverse features. The wide variety of criteria considered, the subjectivity of the qualitative degrees of robusticity, and the ability to recognize them, primarily reflect opinion and practice. Inconsistency in some criteria may stem from the unsatisfactory linking of archaism and robusticity, and the related structure and robusticity. Clearly, for anthropologists, robusticity expresses something stronger and more massive than expected. However, diaphyseal robusticity requires scaled bone to be known, and often this cannot be visually appreciated. Archaic features, shape, non-scaled size, irregular surface and wide topographic variation do not characterize robusticity without supplementary analysis (although muscle activity may act on these structures). The definition of robusticity should be refined and the use of the term robusticity may not be necessary in some circumstances, especially if other terms are sufficient for anatomical description (e.g., shape, size, complexity). We could retain the definition that gives the most coherence to the robusticity concept. Sometimes, the bone is taken as an isolated object and authors attempt to quantify what they see independently of the global (biomechanical) environment of the bone. However, robusticity must be consistent with the living, i.e., biomechanical context. A robust femur "on the desk" must remain so when it is in a functional situation, that is to say, when it is subjected to body weight. It would clearly be difficult to change our practice to keep only the biomechanical application of robusticity. We are confronted with a traditional deeply rooted practice which is very useful to express an impression, an inherently broad concept and difficulties in applying biomechanical approaches to all structures. Robusticity, as it is commonly used, is extremely convenient to encompass a set of data that unfortunately can be of a different nature and not measurable in the same way. Although this diversity of uses in specific applications cannot be avoided, it is strongly recommended to no longer use some criteria, such as size and shape (or to explain how they represent robusticity), or subjective criteria that are difficult to use by diverse observers. Finally, greater consistency should be promoted.

Conclusion

32This brief synthesis was intended to serve as a caution for many prehistorians and others who use the terms robust, robusticity or robustness to relate their observations to human morphology, and as a reminder of certain points for biological anthropologists who do not specialize in aspects of robusticity. It also serves as a call for reflection and change in palaeoanthropological nomenclature practices. While there is a common definition, it can only serve as a starting point. Ultimately, robusticity concerns a wide range of applications associated with various methods and is therefore context-specific. Robusticity is generally determined by additional material over what is expected, or by variations observed on a specific surface that includes bulges and depressions. Clearly, in postcranial studies, "robusticity" represents the level of bone reinforcement above and beyond what is necessary to resist loads in the static posture or during moderate activities. For example, these basic functions include weight-bearing and moderate locomotion in the lower limbs. These studies and related methods can be qualified as biomechanical since they include the cross-sectional geometric properties and appropriate scaling. However, the variety of ways of expressing robusticity is inherent to the concept and to skeleton structure. Many authors do not choose to use a biomechanical quantification of robusticity, which in any case would be difficult to apply to all structures. We are obliged to accept a large part of current practices, but not all of them. The first step would be to standardize practices and avoid using size and shape as synonyms of robusticity.

Acknowledgments: This research was funded by the University of Perpignan (UPVD), Bonus Qualité Recherche 2019 (BQR). I would like to express my gratitude to the various people and institutions who gave me access to computed tomography (CT) and micro-CT imaging archives, and also to those who allowed me to scan bones: Antoine Balzeau (UMR 7194, HNHP) for access to the micro-CT scan archives of the National Museum of Natural History (MNHN, Paris); the AST-RX platform, plateforme d’Accès Scientifique à la Tomographie à Rayons X, UMS 2700 2AD Acquisition et Analyse de Données pour l’histoire naturelle (CNRS-MNHN, Paris); Thomas Colard from the University of Lille; Grégory Hauss and Jerôme Hosdez from the ISIS4D X-ray platform (University of Lille), funded by International Campus on Safety and Intermodality in Transportation (CISIT), the Haut-de-France Region, the European Community and the French National Centre for Scientific Research (CNRS); Patrick Semal from the Royal Belgian Institute of Natural Sciences (Brussels); Henry de Lumley from the Institut de Paléontologie Humaine (Paris) and the Centre Européen de Recherches Préhistoriques (Tautavel); and Jérôme Thomas from the University of Bourgogne (Dijon).

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Table des illustrations

Titre Figure 1
Légende Some non-metric and metric criteria of cranial robusticity. The supraorbital torus of Neandertal (A, blue arrow) is classic evidence of robusticity differentiating Neandertal from Homo sapiens (B). Cranial robusticity is based on very diverse non-metric criteria such as rounding, degree of development, absence/presence and depth: (1) degree of sagittal keeling, (2) development of the supraorbital ridges and formation of a supraorbital torus, (3) depth of the infraglabellar notch, (4) categories of the nasal saddle, (5) rounding of the infero-lateral margin of the orbit, (6) development of the zygomatic trigone, (7) absence or presence of a tubercle on the lateral surface of the mastoid process. Cranial thickness (C), as a variable of robusticity, is often used without scaling |Quelques critères non-métriques et un critère métrique liés à la robustesse crânienne. Le torus supraorbital des Néandertaliens est un témoin classique de robustesse qui permet de les différencier des Homo sapiens (B). La robustesse crânienne est basée sur diverses caractéristiques non-métriques dont l’arrondissement, le degré de développement, l’absence et la présence, ainsi que la profondeur : (1) degré de développement de la carène sagittale ; (2) développement des crêtes supra-orbitaires et la formation du torus supraorbitaire ; (3) profondeur de l’échancrure infra-glabellaire, (4) catégories des os nasaux, (5) arrondissement du bord inféro-latéral de l’orbite, (6) développement du trigone du zygomatique, (7) absence/présence du tubercule sur la surface latérale du processus mastoïdien. L’épaisseur crânienne (C), utilisée comme un critère de robustesse, n’est généralement pas rapportée à une autre dimension
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-1.png
Fichier image/png, 647k
Titre Figure 2
Légende Some metric and non-metric criteria of mandibular robusticity. Mandibular robusticity is usually quantified from coronal cross-sections and described from various non-metric traits, as mentioned in figure 2. Ix: second moment of area about buccolingual axis (superoinferior bending rigidity); Iy: second moment of area about superoinferior axis (buccolingual bending rigidity); K: Bredt’s formula for thin-walled sections (torsional strength); ML: mandibular length; CA: cortical area |Quelques critères métriques et non-métriques liés à la robustesse mandibulaire. La robustesse des mandibules est habituellement quantifiée à partir de sections coronales de la branche horizontale et décrites par divers traits non-métriques, comme indiqué sur la figure 2. Ix : second moment d’aire selon l’axe bucco-lingual (rigidité à la flexion dans le plan supéro-inférieur) ; Iy : second moment d’aire selon l’axe supéro-inférieur (rigidité à la flexion dans le plan bucco-lingual) ; K : formule de Bredt pour les sections à fine paroi (résistance à la torsion) ; ML : longueur mandibulaire ; CA : aire corticale
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-2.png
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Titre Figure 3
Légende Some metric and non-metric criteria of tooth robusticity. A- Metric "crown" robusticity is based on crown and cervical diameters. B- Non-metric crown robusticity is based on discrete traits: the second molar B1 is more robust than B2 considering additive traits. C- Metric root robusticity is based on diameter and root length. D- Root robusticity is often estimated visually; given that large and bulging roots are usually accepted as evidence of robusticity, root D1 presents a more robust morphology than D2. MD: mesiodistal diameter; BL: buccolingual diameter |Quelques critères métriques et non-métriques liés à la robustesse des dents. A- La mesure de la robustesse de la couronne prend en compte les diamètres coronaires et cervicaux. B- La robustesse coronale non-métrique est établie à partir des traits discrets : la seconde molaire B1 est plus robuste que la seconde molaire B2 en raison de la cumulation des traits. C- La mesure de la robustesse racinaire peut se calculer en rapportant le diamètre de la racine à sa longueur. D- La robustesse de la racine est souvent évaluée visuellement ; étant donné que des racines larges et bombées sont généralement acceptées comme une preuve de robustesse, la racine D1 présente une robustesse plus élevée que la racine D2
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-3.png
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Titre Figure 4
Légende Some metric criteria of postcranial robusticity. Many robusticity indices can be measured from one bone. Some measurements represent size or relative size, without appropriate scaling for a biomechanical approach. Robusticity can be quantified at any location on the diaphysis. a AP standardized bending rigidity; b AP standardized bending strength; c standardized torsional rigidity. DAP: anteroposterior diameter; DML: mediolateral diameter; std: standardized; Ix: second moment of area about mediolateral axis (anteroposterior bending rigidity); Zx: section modulus about mediolateral axis (anteroposterior bending strength); J: polar second moment of area (torsional and twice average bending rigidity) |Quelques critères métriques liés à la robustesse du squelette post-crânien. De nombreux indices de robustesse peuvent être mesurés à partir d’un seul os. Certaines mesures ne représentent que la taille ou la taille relative, et ne sont pas correctement standardisées pour une approche biomécanique. Notons que la robustesse peut être quantifiée à n’importe quel niveau sur la diaphyse. a La rigidité à la flexion selon le plan AP, standardisée ; b La résistance à la flexion selon le plan AP, standardisée ;  c La rigidité à la torsion, standardisée. DAP : diamètre antéro-postérieur ; DML : diamètre médio-latéral ; std : standardisé ; Ix : second moment d’aire selon l’axe médio-latéral (rigidité dans le plan antéro-postérieur) ; Zx : Module de section selon l’axe médio-latéral (résistance à la flexion dans le plan antéro-postérieur) ; J : second moment d’aire polaire (rigidité à la torsion et rigidité moyenne à la flexion)
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-4.png
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Titre Figure 5
Légende Some non-metric criteria of postcranial robusticity. The means used to visually assess the degree of bone robusticity are very diverse, subjective and strongly dependent on the observer and his/her conception of robusticity. A quantitative (i.e., biomechanical) method could give distinct results considering the cross-sectional geometric properties of diaphysis, bone length and body mass. A- According to the enthesis scoring method, the Neandertal A2 is more robust than the Upper Palaeolithic modern human A1. B- For many anthropologists, the immature humerus B2 is more robust than humerus B1, given the periosteal diameter/bone length ratio. C- Given its cortical reinforcement, the fibular diaphysis C1 could be considered as more robust than C2. Red represents maximum cortical thickness on the map |Quelques critères non-métriques liés à la robustesse du squelette postcrânien. Les évaluations visuelles du degré de robustesse des os sont très diverses, subjectives et dépendent fortement de l’observateur et de sa conception de la robustesse. Une méthode quantitative (c.-à-d., biomécanique) pourrait donner des résultats distincts en tenant compte des propriétés géométriques de la section transversale de la diaphyse, de la longueur des os et de la masse corporelle. A- Selon la méthode de cotation des enthèses, le Néandertalien A2 est plus robuste que l’Homme moderne du Paléolithique supérieur A1. B- Pour de nombreux anthropologues, l’humérus immature B2 est plus robuste que l’humérus B1 compte tenu du rapport entre le diamètre de la section et la longueur de l’os. C- Étant donné le renforcement cortical de la diaphyse fibulaire C1, elle peut être considérée comme plus robuste que la diaphyse C2. La couleur rouge représente l’épaisseur corticale maximale sur la cartographie
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-5.png
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Titre Figure 6
Légende Surface changes and "morphological robusticity". If we attempt a synthesis of the different practices by visually assessing robusticity, gracility would be a neutral structure (smooth, flat, regularly curved, see A). Any additional material, or less material by sculpting the surface, could be evidence of robusticity. According to this definition of robusticity, structures B and C are more robust than A; D is more robust than A, B and C |Modifications de surface et "robustesse morphologique". Si l’on tente une synthèse des différentes pratiques d’évaluation visuelle de la robustesse, la gracilité serait représentée par une structure neutre (lisse, plate, régulièrement courbée, voir A). Tout apport de matière, ou toute suppression de matière sculptant la surface, pourrait être utilisé comme une preuve de robustesse. Selon cette perception de la robustesse, les structures B et C sont plus robustes que A ; D est plus robuste que A, B et C
URL http://journals.openedition.org/bmsap/docannexe/image/10319/img-6.png
Fichier image/png, 44k
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Tony Chevalier, « The concept of robusticity in (palaeo-) anthropology and its broad range of application: a short review »Bulletins et mémoires de la Société d’Anthropologie de Paris [En ligne], 34 (2) | 2022, mis en ligne le 21 octobre 2022, consulté le 27 novembre 2022. URL : http://journals.openedition.org/bmsap/10319 ; DOI : https://doi.org/10.4000/bmsap.10319

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Tony Chevalier

UMR 7194 Histoire Naturelle de l’Homme Préhistorique, Université de Perpignan Via Domitia, MNHN/CNRS, EPCC-Centre de Recherches Préhistoriques de Tautavel, France ; tony.chevalier[at]cerptautavel.com ; https://orcid.org/0000-0001-6936-816X

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