Archaic and modern human distal humeral morphology

Journal of Human Evolution 51 (2006) 603e616

Archaic and modern human distal humeral morphology Todd R. Yokley*, Steven E. Churchill Department of Biological Anthropology and Anatomy, Duke University, Durham, North Carolina 27708, USA Received 16 October 2002; accepted 5 July 2006

Abstract The morphology of the proximal ulna has been shown to effectively differentiate archaic or premodern humans (such as Homo heidelbergensis and H. neanderthalensis) from modern humans (H. sapiens). Accordingly, the morphology of adjacent, articulating elements should be able to distinguish these two broad groups as well. Here we test the taxonomic utility of another portion of the elbow, the distal humerus, as a discriminator of archaic and modern humans. Principal components analysis was employed on a suite of log-raw and log-shape distal humeral measures to examine differences between Neandertal and modern human distal humeri. In addition, the morphological affinities of Broken Hill (Kabwe) E.898, an archaic human distal humeral fragment from the middle Pleistocene of Zambia, and five Pliocene and early Pleistocene australopith humeri were assessed. The morphometric analyses effectively differentiated the Neandertals from the other groups, while the Broken Hill humerus appears morphologically similar to modern human distal humeri. Thus, an archaic/modern human dichotomydas previously reported for proximal ulnar morphologydis not supported with respect to distal humeral morphology. Relative to australopiths and modern humans, Neandertal humeri are characterized by large olecranon fossae and small distodorsal medial and lateral pillars. The seeming disparity in morphological affinities of proximal ulnae (in which all archaic human groups appear distinct from modern humans) and distal humeri (in which Neandertals appear distinct from modern humans, but other archaic humans do not) is probably indicative of a highly variable, possibly transitional population of which our knowledge is hampered by sample-size limitations imposed by the scarcity of middle-to-late Pleistocene premodern human fossils outside of Europe. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Humerus; Human paleontology; Archaic humans; Neandertals; Broken Hill; Kabwe

Introduction Neandertals and other archaic humans (such as Homo heidelbergensis and H. erectus) have been shown to differ from recent and most early modern humans (H. sapiens) with respect to aspects of elbow morphology. These differences have been observed in each of the three primary components of the elbow: the proximal ulna (Trinkaus, 1983a; Churchill et al., 1996; Pearson and Grine, 1996; Groves, 1998; Pearson et al., 1998), proximal radius (Trinkaus, 1983a,b; Trinkaus and * Corresponding author. Department of Biological Anthropology and Anatomy, Box 90383, Duke University, Durham, NC 27708-0383, USA. Tel.: þ1 919 660 7395; fax: þ1 919 660 7348. E-mail addresses: [email protected] (T.R. Yokley), [email protected] (S.E. Churchill). 0047-2484/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jhevol.2006.07.006

Churchill, 1988), and distal humerus (Pearson and Grine, 1996; Pfeiffer and Zehr, 1996; Churchill and Smith, 2000). Proximal ulnar morphology, in particular, has been shown to be an effective discriminator of archaic and modern humans (Churchill et al., 1996; Pearson and Grine, 1996; Groves, 1998; Pearson et al., 1998), with archaic humans exhibiting a suite of features not typically found among modern humans. These features include an anteroposteriorly high and proximodistally long olecranon process, a distally placed m. brachialis tuberosity, a mediolaterally wide and anteroposteriorly narrow proximal shaft, a relatively short (anteroposteriorly) coronoid process, and an anteriorly (as opposed to anteroproximally) oriented trochlear notch (Churchill et al., 1996). In light of these differences between archaic and modern human ulnae and the presumed functional and morphological interdependence of the components of the elbow, the articular

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and periarticular areas of other adjacent bones may be predicted to exhibit similar levels of divergence. Accordingly, the morphology of the distal humerus should also differentiate archaic and modern humans. Distal humeral anatomy has previously been used in taxonomic and phylogenetic analyses of early hominins (Senut, 1981; Lague and Jungers, 1996; Bacon, 2000), but use of the humerus in studies of more recent human groups has been limited primarily to osteometric and diaphyseal dimensions of the entire bone (e.g., Churchill, 1994; Churchill and Smith, 2000). Taphonomic processes rarely leave fossil humeri undamaged, however, and specimens are often excluded from analyses due to lack of preservation. An analysis focusing only on the distal humerus allows for the inclusion of partial specimens, therefore expanding sample size and producing more reliable results. Moreover, the highly dense bone of the distal humerus makes it one of the most commonly preserved elements in fossil human assemblages, and knowledge of taxonomic differences in distal humeral morphology would certainly prove valuable. We assess these differences in the present analysis.

Materials and methods In order to investigate differences in distal humeral morphology, we analyzed a sample of 238 fossil and recent human distal humeri, which we divided into four primary groups. Modern humans (n ¼ 213) constituted the largest subdivision of this sample (Table 1). This group included early modern humans from Middle Paleolithic western Asia (Skhul and Qafzeh, n ¼ 3), early Upper Paleolithic Europe (>20 ka, EUP, n ¼ 20), late Upper Paleolithic Europe (20 ka, LUP, n ¼ 24), Mesolithic Europe (n ¼ 13), and Later Stone Age southern Africa (LSA, n ¼ 34), as well as recent human Peruvians (n ¼ 24, from the National Museum of Natural History, Smithsonian Institution), American blacks (n ¼ 50, from the Terry Collection at the National Museum of Natural History), and American whites (n ¼ 45, from the Maxwell Museum of Anthropology and the Terry Collection). The principal group of archaic humans included in our sample contained 19 Neandertal humeri from Europe and the Near East (Table 2). The second archaic group in our analysis included a single specimen, an African archaic human humerus from Zambia: Broken Hill (Kabwe) E.898 (Fig. 1; Pycraft et al., 1928). We chose to include the Broken Hill humerus because it represents the only well-described distal humerus from the middle Pleistocene of Africa.1 While multiple taxonomic names have been used to classify the African hominins that lived during this time period (typically H. heidelbergensis, H. rhodesiensis, or H. sapiens rhodesiensis), nearly all scholars (e.g., Rightmire, 1998; Stringer, 2002) agree that this group is broadly ancestral to both Neandertals and modern humans. Since Broken Hill E.898 is the best-known distal 1

A distal humeral fragment has been recovered from the middle Pleistocene site of Bodo in Ethiopia (Clark et al., 1994), although measurements of this specimen have yet to be published.

humeral fragment assigned to this group, it is the best candidate we have for the morphology of the last common ancestor of Neandertals and modern humans. However, the details of the discovery of this specimen are not well-known, and its designation should be made with due caution. Broken Hill E.898 is believed to have been discovered in 1921, along with the other human remains from the site (Hrdlicka, 1926, 1930; Pycraft et al., 1928), but it was not recognized as human until Hrdlicka visited the mining site four years later (Hrdlicka, 1926, 1930). The Broken Hill humerus almost certainly comes from the same deposits as the more famous Broken Hill cranium (E.686), although these two specimens may or may not be from the same individual [compare Pycraft et al. (1928) to Hrdlicka (1930)]. While the exact age of these deposits has never been established, they are widely considered to be later-early or middle Pleistocene in origin (Klein, 1973, 1994; Rightmire, 1990; McBrearty and Brooks, 2000, and references therein). By assessing the affinities of the archaic human humerus from this site, we can better determine if distal humeral differences between Neandertals and modern humans are indicative of a larger archaic/modern human dichotomy. However, due to the questionable circumstances under which the Broken Hill humerus was discovered, we acknowledge the possibility that it may be of recent origin and therefore not representative of the morphology of middle Pleistocene African populations. Nevertheless, for the purpose of this analysis, we will proceed under the assumption that it is of middle Pleistocene origin. The fourth and final group in our analysis comprised five australopith humeri (Table 2). These specimens included KNM-ER 739 and KNM-ER 1504 (East Turkana, Kenya), KNM-KP 271 (Kanapoi, Kenya), A.L. 288-1m (Hadar, Ethiopia), and TM 1517 (Kromdraai, South Africa). Although these specimens come from multiple species, incorporating them into our analysis should give us an idea of the ancestral morphology from which that of the genus Homo evolved and should further help in establishing the polarity of features seen in archaic and modern human humeri. We chose a set of twelve linear measurements to represent the articular and epiarticular aspects of the distal humerus. These measurements included bi-epicondylar breadth (EB), mediolateral trochlear breadth (TB), anteroposterior width of the medial trochlea (MTW), anteroposterior width of the lateral trochlea (LTW), minimum anteroposterior width of the trochlea (TW), capitular breadth (CB), anteroposterior capitular depth (CAP), superoinferior capitular depth (CSI), mediolateral diameter of the olecranon fossa (OFML), superoinferior diameter of the olecranon fossa (OFSI), and the distodorsal diameters of the medial pillar (MP) and lateral pillar (LP) (Fig. 2). All measurements were taken by S.E.C. on original skeletal material except for the five australopith specimens, for which high quality casts were used. Because shrinkage and distortion of casts can alter their size and shape, we compared dimensions from our casts to equivalent measurements taken on original specimens published by Senut (1981). Senut’s measurements included six of the twelve that we used in our analysis. Differences between our measurements and

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Table 1 The modern human sample Sample

Males

Females

Middle Paleolithic western Asia

Skhul 4 Skhul 5

Qafzeh 3

Early Upper Paleolithic Europe

Abri Pataud 4 Arene Candide 1 Barma Grande 2, 5 Bausso del Torre 2 Cro-Magnon 1, 3 Dolnı´ Veˇstonice 13, 14, 16 Grotte des Enfants 4, 6 La Rochette 1 Paviland 1

Barma Grande 3 Dolnı´ Veˇstonice 15 Grotte des Enfants 5 Nahal Ein Gev 1 Paglicci 25

Abri Pataud 5

Late Upper Paleolithic Europe

Arene Candide 2, 4, 5, 10, 12 Le Placard 16a Neuessing 2 Oberkassel 1 Romanelli 1 Veyrier 1, 7

Arene Candide 3, 13, 14 Bruniquel 24 Cap Blanc 1 Oberkassel 2 Romito 3, 4 St. Germain-la-Rivie`re 4 Veyrier 10

La Madelaine Romanelli 2, 4

Mesolithic Europe

Hoe¨dic 5, 6, 9 Rochereil 1 Teviec 8, 11, 16 Gramat 1

Hoe¨dic 8 Gough’s Cave 1 Teviec 1, 9

Paviland 2

Later Stone Age southern Africa

Matjes River (n ¼ 17)

Matjes River (n ¼ 9)

Matjes River (n ¼ 8)

Recent human

American black (n ¼ 25) American white (n ¼ 24)

American black (n ¼ 25) American white (n ¼ 21)

Peruvian (n ¼ 24)

a

Sex uncertain

Presumed male (see Churchill, 1994).

Senut’s were generally less than 5% and varied both positively and negatively. We thus concluded that substantial shrinkage of the casts had not occurred and that the measurements were suitable for use in our analysis. Due to the limited number of specimens in the fossil record, we incorporated individuals of both sexes into our sample of distal humeri. Numbers of males and females often differed substantially for each group (Tables 1 and 2). When both humeri of an individual were equally complete, the right humerus was preferentially selected. Bilateral asymmetry in

distal humeral articular dimensions (Trinkaus et al., 1994) and bi-epicondylar breadth (Churchill, unpublished data) is generally less than 2% in both recent and archaic humans, so unequal representations of sides are not expected to influence results. In the case of differential preservation, we chose to use the measurements from the more complete side. Where necessary, missing values on one side were substituted with corresponding values from the opposite side. In order to assess variation in our sample, we employed covariance-based principal components analysis (PCA), which

Table 2 Neandertal, African archaic, and australopith samples Sample Neandertal

Males

Females a

Krapina 160, 161, 169, 170 La Chappelle 1 La Ferrassie 1 Neandertal 1 Spy 2

Krapina 159, 166, 174 La Ferrassie 2 La Quina 5 Lezetxiki 1b Spy 1 Tabun C1

African Archaic Australopith

a b

Sex attribution following Trinkaus (1980). Presumed female (see Churchill, 1994).

Sex uncertain a

Krapina 162, 165, 171

Broken Hill E.898 A.L. 288-1

KNM-ER 739 KNM-ER 1504 KNM-KP 271 TM 1517

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Fig. 1. The Broken Hill E.898 humerus in anterior view.

has been shown to be a highly effective means of revealing multivariate relationships (Falsetti et al., 1993). Following the procedure outlined by Darroch and Mosimann (1985), we ran PCAs on two sets of data: 1) log-raw variables, which contain information on both size and shape, and 2) log-shape variables, which contain information on shape alone (see also Falsetti et al., 1993). The log-shape variables were generated by logging ratios of the raw variables to the geometric mean of all variables for each individual. In addition to revealing differences in size and shape combined and differences in shape alone, this procedure allows the percentage of variance in a sample due to size and the percentage due to shape to be calculated. As is usually the case when working with fragmentary fossil samples, the problem of missing data had to be addressed before the analyses were performed. As in most multivariate procedures, PCA requires that no gaps be present in the data matrix. To deal with this problem, two steps were taken: 1) we only included specimens for which eight or more of the twelve measurements could be taken, and 2) for each variable, we used multiple regression on the remaining variables to predict the missing values. We used our entire sample in the regression analysis because we believe this type of approach minimizes the effect of false group differences and is thus preferable to using subgroup data. Predicted values were

inserted into the data matrix before the statistical analyses were performed. This procedure allowed us to incorporate 34 specimens into our analysis that otherwise would be unusable. In addition to analyzing the individual data, we also used PCA to analyze the log-raw and log-shape group means of the twelve variables (see Groves, 1998). If we assume that the mean value of each of our measurements provides an adequate representation of the true group average, a PCA of these mean values will show the primary factors that are driving group differences. This procedure treats each group as if it had an equal number of members and therefore allows for an equal contribution from each group to the analysis. We used the mean values of the eight modern human subgroups instead of the overall mean so that variation within the modern human sample could be investigated. The PCAs were performed using the software package SPSS 12.0 (SPSS Inc., Chicago, IL). Canonical variates analysis (CVA) or other discriminatory methods may seem more appropriate for assessing group differences, but when CVA is performed on log-shape variables, there is a problem with matrix singularity that causes statistical software to drop the last row and column of the pooled within-class covariance matrix (Falsetti et al., 1993). Darroch and Mosimann (1985) outlined a series of cumbersome calculations to get around this problem, but considering that a CVA on our log-raw data produces very similar results to the lograw PCAs we performed on both the individual and group data, we felt that this procedure added little to our overall assessment of distal humeral variation and therefore did not include it in our analysis. Lastly, we calculated a Euclidean distance matrix from the eleven group means of the log-shape variables and used these distances as the basis for a hierarchical cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) (Sneath and Sokal, 1973). The distance matrix provided us with a more precise means of measuring differences between groups, while UPGMA clustering provided a graphic representation of the distance matrix in the form of a dendrogram. These analyses were performed using the software package NTSYSpc 2.20e (Rohlf, 2005). Results Means and standard deviations of the twelve measurements are listed in Tables 3 and 4. Table 3 lists the overall group averages along with the male and female averages for each of the four primary groups, while Table 4 does likewise for the modern human subgroups. Bi-epicondylar breadth is greatest in Broken Hill E.898 and the Neandertals. These two groups are also similar in terms of their great trochlear and capitular breadths. The diameters of the olecranon fossa and distodorsal pillars of the Neandertals and Broken Hill E.898, however, are quite different. In comparison to the Broken Hill humerus, the average Neandertal olecranon fossa diameters are large, while the average distodorsal pillar diameters are small. Modern humans, who generally have small bi-epicondylar breadths relative to the Neandertals, also exhibit larger distodorsal pillars.

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Fig. 2. Measurements used in this study. Martin numbers (M-no.; Martin, 1928) provided where appropriate. EB: bi-epicondylar breadth (M-4); TB: mediolateral trochlear breadth (M-11); MTW: medial trochlear width (A-P width of the medial margin of the trochlea); LTW: lateral trochlear width (A-P width of the lateral margin of the trochlea); TW: least trochlear width (minimum A-P width of the trochlea); CB: capitular breadth (M-L diameter of the capitular articular surface); CAP: anteroposterior capitular depth (A-P diameter of the capitulum); CSI: superoinferior capitular depth (S-I diameter of the capitular articular surface); OFML: mediolateral olecranon fossa diameter (M-14); OFSI: superoinferior olecranon fossa diameter (S-I diameter of the olecranon fossa); MP: distodorsal medial pillar diameter (diameter of the distodorsal medial pillar taken at the midpoint of the adjacent olecranon fossa margin); LP: distodorsal lateral pillar diameter (diameter of the distodorsal lateral pillar taken at the midpoint of the adjacent olecranon fossa margin).

The PCA of the log-raw data produced twelve principal components with a total variance of 0.03891. The first six of these components account for 92.9% of the variance and are characterized in Table 5. The first principal component (PC) is positively correlated with all of the log-raw variables and therefore most likely represents size and size-correlated shape. This component reveals no major differences among the groups, with modern humans exhibiting a range that spans that of virtually the entire sample (Fig. 3). Unlike PC 1, PC 2 exhibits both positive and negative correlations with the log-raw variables. Nine variables are significantly positively correlated with PC 2 at a ¼ 0.01, with OFML (0.640) and OFSI (0.570) possessing the highest correlations. Only one variable, MP (0.604), is significantly negatively correlated with PC 2 at a ¼ 0.01, although LP (0.102) also exhibits a negative, albeit insignificant, correlation. The Neandertals tend to fall toward the high end of PC 2 (Figs. 3 and 4), and collectively they exhibit a mean position along this axis of 1.562. Modern humans possess a mean position substantially less than that of the Neandertals, although the range of these two samples overlap somewhat. The position of Broken Hill E.898 along PC 2 (0.173) is very close to the modern human mean (0.103). The australopiths fall toward the low end of PC 2 and have a mean position of

1.567. On the basis of the respective positions of the groups on PC 2, the correlations suggest that Neandertals possess relatively wider and taller olecranon fossae and narrower medial pillars than modern humans, Broken Hill E.898, and the australopiths. The mean positions along PC 3 appear to separate the australopiths from the other three groups, but the high australopith average is primarily due to the extreme position of KNM-ER 1504. Plotting the australopiths along PC 3 (Fig. 4) reveals that, with the exception of KNM-ER 1504, these specimens are not divergent from the rest of the specimens in this analysis. One other specimen (Skhul 4) exhibits a fairly extreme position along PC 3. On the basis of correlations between PC 3 and the original variables, the extreme position of these two specimens is due primarily to mediolaterally wide trochlear breadth and narrow minimum trochlear width, which was previously noted for KNM-ER 1504 by Lague and Jungers (1996). Principal components 4e6 account for 11.3% of the variance in the data. None of these three principal components show much separation of the groups. The PCA on the log-shape data produced a total variance of 0.01665, which is 42.8% of the log-raw total variance. This indicates that size variation alone accounts for 57.2% of the

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Table 3 Group means and standard deviations of the twelve variables Modern humans

Neandertals

Australopiths (5)

Broken Hill E.898

Total (213)

Males (101)

Females (74)

Total (19)

Males (8)

Females (8)

Bi-epicondylar breadth

58.6 (206) 5.4

61.4 (97) 5.2

55.7 (72) 4.0

62.5 (13) 4.1

64.9 (7) 2.0

58.5 (5) 3.2

56.4 10.8

62.0 d

Trochlear breadth

20.8 (211) 2.6

22.1 (100) 2.7

19.7 1.8

21.0 2.2

22.3 1.9

20.4 1.9

20.4 4.1

22.6 d

Medial trochlear width

24.7 (202) 3.1

26.2 (97) 3.2

23.3 (72) 2.1

24.2 (16) 2.9

26.2 2.3

22.3 (6) 2.1

21.6 3.9

26.3 d

Lateral trochlear width

18.7 (208) 2.2

19.8 (99) 2.2

17.6 (72) 1.9

18.1 (17) 1.5

19.2 1.0

16.9 (6) 0.6

17.8 4.6

21.1 d

Least trochlear width

16.2 (212) 2.0

17.2 2.0

15.3 1.7

15.2 1.0

16.0 0.7

14.5 0.9

12.8 1.4

18.1 d

Capitular breadth

21.3 (212) 2.3

22.3 (100) 2.3

20.3 1.9

22.0 (17) 1.6

23.1 1.1

21.0 1.4

18.8 3.2

24.0 d

Capitular A-P depth

23.4 (209) 2.8

24.8 (99) 2.8

22.3 (73) 2.2

23.4 (17) 2.0

24.7 1.1

22.4 (7) 1.9

19.7 4.0

25.8 d

Capitular S-I depth

19.9 (208) 2.2

21.2 (99) 2.2

19.0 (71) 1.6

18.8 (18) 1.9

20.2 1.4

18.1 1.3

17.9 4.0

21.8 d

Olecranon fossa M-L diameter

24.8 (211) 2.3

25.7 (100) 2.3

23.9 1.7

28.1 1.7

28.4 2.0

28.1 1.7

22.0 4.0

24.7 d

Olecranon fossa S-I diameter

17.8 (211) 2.0

18.4 (100) 2.1

17.2 (73) 1.7

19.7 (18) 1.4

20.0 1.1

19.7 (7) 1.7

16.7 2.3

18.7 d

Distodorsal medial pillar diameter

10.8 (203) 2.1

11.6 (96) 2.1

9.9 (69) 1.7

8.2 (17) 2.2

9.4 1.5

7.8 (6) 2.4

11.6 2.5

11.7 d

Distodorsal lateral pillar diameter

17.6 (203) 2.7

18.7 (96) 2.9

16.6 (69) 2.0

16.0 (17) 2.8

17.2 1.9

14.8 (6) 1.4

15.9 3.1

18.5 d

All measurements in millimeters. Overall group means include individuals of uncertain sex. Sample sizes indicated in parentheses. Data are displayed as follows: the mean is the first entry in a cell; the number of individuals used to calculate the mean is listed in parentheses alongside the mean when less than the total sample was used; the standard deviation is below the mean.

overall variation. Table 6 lists the first six principal components, which account for 88.7% of the log-shape variance. Principal component 1 in this analysis is similar to PC 2 in the log-raw data analysis in that it contrasts the dimensions of the olecranon fossa with the size of the distodorsal pillars. However, unlike in the previous analysis, the negative correlation between PC 1 and LP is significant. As with the log-raw PC 2, the Neandertals are fairly divergent from the other groups along PC 1 (Fig. 5). The Neandertals tend to exhibit higher values, although there is again some overlap with the modern human sample. These results suggest that, for a given size (i.e., geometric mean), Neandertals possess large olecranon fossae and narrow distodorsal pillars relative to modern humans, Broken Hill, and the australopiths. Despite a large negative mean for the australopiths, PC 2 does not exhibit much divergence between the groups. As was true of the log-raw PC 3, the average australopith position on PC 2 is mainly due to the extreme position of KNM-ER 1504. The higher principal components again show little group separation. We also ran PCAs on the group means of both the log-raw and log-shape variables. As outlined earlier, the purpose of this procedure is to hold group size constant, so that each group

contributes equally to the analysis. By performing PCAs on the log-raw and log-shape group means, we can determine if variation in group size had any effect on the results of the total sample PCAs. According to these analyses, group size had little effect on the outcome. The results are similar to those presented earlier, although the primary group differences are captured in two components rather than one (Tables 7 and 8) and variation in shape is responsible for a slightly higher percentage (49.4%) of the overall variation. Once again, Neandertals are separated from the other groups on the log-raw PC 2 (Figs. 6 and 7) and the log-shape PC 1 (Fig. 8). However, they are also separated from most of the groups on the lograw PC 3 (Fig. 7) and the log-shape PC 2 (Fig. 8) as well. The log-raw PC 2 exhibits significant correlations with OFSI (0.623) and MP (0.951), while the log-raw PC 3 is significantly correlated with OFML (0.788). The log-shape PC 1 exhibits significant correlations with OFSI shape (0.712), MP shape (0.992), LP shape (0.621), and CB shape (0.644), while the log-shape PC 2 is significantly correlated with OFML shape (0.830), EB shape (0.891), TB shape (0.622), and CSI shape (0.750). These results support our finding that Neandertal humeri have tall, broad olecranon fossae and narrow distodorsal pillars relative to those of modern

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Table 4 Modern human subgroup means and standard deviations of the twelve variables (a) Skh ul-Qafzeh, early Upper Paleolithic (EUP), and late Upper Paleolithic (LUP) samples Skhul-Qafzeh Total (3)

Males (2)

EUP

Females (1)

Total (20)

Males (14)

LUP Females (5)

Total (24)

Males (11)

Females (10)

Bi-epicondylar breadth

61.2 3.8

63.3 2.1

57.2 d

59.6 (19) 5.6

61.0 (13) 5.4

56.8 5.9

59.3 (21) 3.8

61.5 (10) 2.5

55.9 (8) 3.0

Trochlear breadth

21.8 4.9

24.0 4.2

17.4 d

20.8 2.0

21.5 2.0

19.6 1.0

20.2 1.4

20.8 1.5

19.5 1.2

Medial trochlear width

24.2 (2) 4.0

27.0 (1) d

21.3 d

26.4 (17) 2.7

27.5 (12) 2.4

24.4 (4) 2.0

24.6 2.0

25.7 1.6

23.2 1.6

Lateral trochlear width

17.3 (2) 1.0

18.0 (1) d

16.6 d

19.3 (18) 2.6

20.2 (12) 2.5

17.2 1.6

19.0 (22) 1.8

20.1 1.6

17.9 (8) 1.5

Least trochlear width

15.8 2.9

16.4 3.8

14.6 d

17.8 2.7

18.3 2.9

16.2 2.3

16.5 1.8

17.5 1.3

15.4 1.9

Capitular breadth

19.9 3.4

19.4 4.6

20.9 d

23.0 2.3

23.6 2.1

21.2 2.4

21.5 (23) 2.3

22.1 (10) 1.6

20.6 2.8

Capitular A-P depth

22.3 3.3

23.5 3.8

20.0 d

24.2 2.8

24.6 2.9

23.1 2.7

23.8 (22) 2.3

25.4 (10) 2.1

22.2 (9) 1.6

Capitular S-I depth

18.1 (2) 2.0

19.5 (1) d

16.7 d

21.0 (19) 2.4

21.6 2.1

19.0 (4) 2.7

20.4 (23) 1.7

21.2 (10) 1.9

19.6 1.4

Olecranon fossa M-L diameter

27.2 (2) 0.2

27.2 0.2

d

25.8 2.3

25.9 2.5

25.6 2.4

25.0 1.9

25.4 2.1

24.4 1.9

Olecranon fossa S-I diameter

16.4 (2) 2.4

16.4 2.4

d

19.0 (19) 2.2

19.4 2.2

17.3 (4) 1.7

17.3 1.9

17.5 2.0

16.7 1.7

Distodorsal medial pillar diameter

13.7 (2) 1.3

13.7 1.3

d

10.6 (16) 2.0

11.2 (12) 2.0

8.9 (3) 0.9

10.3 (19) 1.8

10.6 (9) 2.1

9.9 (7) 1.5

Distodorsal lateral pillar diameter

17.5 (2) 0.5

17.5 0.5

d

17.9 (16) 2.9

18.3 (12) 3.2

16.4 (3) 0.9

17.3 (19) 2.4

17.7 (9) 2.0

16.0 (7) 2.5

(b) Mesolithic, Later Stone Age (LSA), and Peruvian samples Mesolithic

LSA Females (4)

Total (34)

Males (17)

Peruvian (24)

Total (13)

Males (8)

Females (9)

Bi-epicondylar breadth

59.2 (11) 4.4

61.1 (6) 4.1

55.4 2.0

53.1 4.4

55.0 4.2

48.9 2.1

56.3 (23) 4.6

Trochlear breadth

21.3 (12) 2.5

21.9 (7) 2.5

19.9 2.4

18.7 2.2

19.3 2.1

16.9 1.1

19.3 (23) 1.7

Medial trochlear width

25.6 (11) 2.6

26.5 (7) 2.9

23.6 (3) 1.1

20.9 2.1

21.5 1.9

19.3 1.8

23.3 (19) 2.0

Lateral trochlear width

19.2 1.9

20.2 1.2

16.9 1.5

16.2 1.8

17.0 1.5

14.4 0.9

17.9 1.4

Least trochlear width

17.2 (12) 1.5

17.8 1.3

15.9 0.9

15.1 1.7

15.9 1.7

13.6 0.9

15.4 1.5

Capitular breadth

18.7 2.6

18.7 2.3

18.2 3.6

20.3 2.0

21.0 2.2

18.9 1.3

20.2 1.8

Capitular A-P depth

21.0 (12) 2.3

21.3 (7) 1.4

20.0 3.4

20.9 2.1

22.0 2.1

19.0 0.9

21.7 (23) 1.6

Capitular S-I depth

20.0 (12) 1.7

20.6 1.1

17.7 (3) 1.2

17.7 (33) 1.72

18.5 1.8

16.3 (8) 1.3

18.1 1.2

Olecranon fossa M-L diameter

25.2 1.9

25.2 2.1

24.4 0.4

24.0 2.2

24.3 2.2

22.7 1.5

22.9 (23) 2.3

Olecranon fossa S-I diameter

18.8 1.6

19.2 1.8

17.7 0.8

17.0 1.6

17.4 1.5

16.1 1.9

16.5 1.5 (continued on next page)

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616

610 Table 4 (continued )

(b) Mesolithic, Later Stone Age (LSA), and Peruvian samples Mesolithic Total (13)

Males (8)

LSA Females (4)

Total (34)

Peruvian (24)

Males (17)

Females (9)

Distodorsal medial pillar diameter

10.9 2.0

11.6 1.3

9.9 3.0

9.3 2.0

9.5 2.1

8.1 1.8

10.7 1.7

Distodorsal lateral pillar diameter

17.9 1.7

18.3 1.2

16.4 1.8

15.2 2.0

15.8 2.2

13.8 1.4

16.7 2.1

(c) American black and white samples American black

American white

Total (50)

Males (25)

Females (25)

Total (45)

Males (24)

Females (21)

Bi-epicondylar breadth

61.0 4.4

64.3 3.5

57.8 2.1

60.0 5.5

63.6 4.3

55.9 3.4

Trochlear breadth

22.3 2.6

24.2 2.3

20.4 1.2

21.6 2.3

22.8 2.0

20.1 1.7

Medial trochlear width

26.4 2.8

28.6 2.3

24.3 1.2

25.4 2.4

26.9 1.9

23.7 1.6

Lateral trochlear width

19.5 2.1

20.8 2.0

18.1 1.2

19.5 1.8

20.4 1.5

18.5 1.7

Least trochlear width

16.6 2.0

17.8 1.7

15.4 1.6

16.1 1.7

16.7 1.5

15.3 1.6

Capitular breadth

21.9 1.9

23.1 1.5

20.6 1.5

22.0 2.0

23.3 1.4

20.5 1.4

Capitular A-P depth

24.4 2.3

26.1 1.8

22.7 1.3

25.2 2.3

26.7 1.8

23.5 1.5

Capitular S-I depth

21.0 2.0

22.5 1.5

19.6 1.0

20.6 1.9

21.8 1.5

19.2 1.2

Olecranon fossa M-L diameter

25.3 2.0

26.2 2.2

24.3 1.2

25.0 2.6

26.5 2.3

23.3 1.8

Olecranon fossa S-I diameter

17.8 1.9

18.0 2.1

17.5 1.7

18.5 1.9

19.3 1.8

17.6 1.7

Distodorsal medial pillar diameter

11.6 2.0

12.9 1.9

10.3 1.1

11.3 1.8

12.0 1.5

10.4 1.8

Distodorsal lateral pillar diameter

19.6 2.4

21.2 2.0

17.9 1.4

17.8 2.4

19.0 2.3

16.5 1.7

All measurements in millimeters. Overall group means include individuals of uncertain sex. Data are displayed as in Table 3.

humans, Broken Hill, and the australopiths in both absolute and shape dimensions. The Euclidean distance matrix that was calculated from the eleven group means of the log-shape variables is presented in Table 9. With most distances greater than 0.15, the Neandertals show the greatest amount of shape difference from the other groups. The Skh ul-Qafzeh and australopith samples are also fairly different from the other groups, but as was the case with the PCAs, this result is probably due to the extreme positions of Skh ul 4 and KNM-ER 1504 and the limited number of individuals in these groups. With the exception of the Skh ul-Qafzeh and Mesolithic samples, most of the modern human groups show distances from other modern groups less than 0.10. Broken Hill shows the greatest similarities with the modern human groups. These results are mirrored in the UPGMA dendrogram (Fig. 9). The Neandertals show the greatest amount of morphological

distance and serve as an outgroup to the other groups. The EUP and LUP samples show the least amount of morphological distance and cluster together. Broken Hill is most similar to the modern human groups and clusters with the American white, American black, Peruvian, EUP, and LUP samples. The australopith and Skhul-Qafzeh samples cluster together, once again reflecting the similarities between Skh ul 4 and KNM-ER 1504. Discussion The Neandertals are the most distinct of the four primary groups in this analysis in terms of both log-raw and log-shape measures. The most prominent differences between Neandertals and the other groups are the Neandertals’ relatively large olecranon fossae and narrow distodorsal medial and lateral pillars. Given that previous studies (Churchill et al., 1996;

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616 Table 5 Results of the PCA on the log-raw data Principal component

4

Eigenvalue

1 2 3 4 5 6

% total variance explained

0.02404 0.00571 0.00198 0.00180 0.00143 0.00117

Total PC 1

PC 2

3

61.8 14.7 5.1 4.6 3.7 3.0

0.03613

Mean group position

2

1

92.9

PC 3

PC 4

PC 5

PC 6

-4

-3

-2

-1

0

0.438 1.562 0.755 0.201 0.452 0.049 0.053 0.103 0.097 0.009 0.041 0.001 0.885 0.173 0.622 0.633 0.294 0.233 0.756 1.567 1.371 0.271 0.025 0.179

-1

Loadings

PC 2

-2

EB TB MTW LTW TW CB CAP CSI OFML OFSI MP LP

0.898* 0.162** 0.795* 0.124 0.895* 0.185* 0.871* 0.185* 0.726* 0.246* 0.716* 0.268* 0.858* 0.216* 0.887* 0.167* 0.461* 0.640* 0.439* 0.570* 0.775* 0.604* 0.841* 0.102

PC 3

PC 4

PC 5

PC 6

0.141** 0.421* 0.022 0.103 0.429* 0.282* 0.137** 0.091 0.348* 0.345* 0.084 0.053

0.185* 0.001 0.058 0.221* 0.230* 0.016 0.054 0.008 0.163** 0.334* 0.126 0.458*

0.029 0.089 0.175* 0.145** 0.277* 0.505* 0.283* 0.061 0.118 0.008 0.064 0.166**

0.021 0.304* 0.141** 0.135** 0.095 0.057 0.101 0.126 0.059 0.454* 0.062 0.183*

*Correlation is significant at the 0.01 level (two-tailed test). **Correlation is significant at the 0.05 level (two-tailed test).

Pearson and Grine, 1996; Groves, 1998; Pearson et al., 1998) have shown that Neandertal and modern human proximal ulnae differ substantially, distal humeral differences between these two groups are not surprising. However, unlike these previous studies, the African archaic human specimen in our analysis, Broken Hill E.898, was found to be morphologically more similar to modern humans than to the Neandertals. In contrast to this finding, the studies on proximal ulnar morphology revealed that the African archaic human ulna from Baringo (KNM-BK 66; Churchill et al., 1996; Groves, 1998; Pearson et al., 1998) and the early modern human ulnae from Klasies River Mouth (Churchill et al., 1996; Groves, 1998; Pearson et al., 1998) and Border Cave (Pearson and Grine, 1996) are morphologically more similar to Neandertals. While the disparity in these results may be indicative of temporally mosaic evolution of modern human elbow morphology, with modern distal humeral morphology evolving prior to modern proximal ulnar morphology, this scenario seems unlikely. Churchill et al. (1996) found that Neandertal (and other archaic human) ulnae tend to have proximodistally long and anteroposteriorly high olecranon processes relative to modern humans. Fittingly, the major distal humeral differences between Neandertals and other human groups appear to be related to size of the olecranon fossa. Our results suggest that, relative to modern humans, Neandertal humeri had mediolaterally wide and proximodistally tall olecranon fossae and narrow distodorsal medial and lateral pillars. During extension of

PC 1 (61.8

0

Neandertals Modern humans Broken Hill E.898 Australopiths PC 1

611

1

2

)

3

4

Modern Humans Neandertals

-3

Broken Hill Australopiths

PC 2 (14.7

-4

)

Fig. 3. Bivariate plot of PC 1 and PC 2 of the log-raw PCA.

the forearm, the anterior face of the olecranon process rests inside the olecranon fossa and is bounded on either side by the two distodorsal pillars. Due to the apparent functional interdependence of these features, aspects of this morphological complex should change in a coordinated fashion over time. In order to evaluate this assessment, we computed the product-moment correlation coefficient (Sokal and Rohlf, 1995) between olecranon fossa superoinferior diameter and olecranon process superoinferior length (one of the ulnar measurements used by Churchill et al., 1996) using a sample of 62 4

3

2

1 PC 2 (14.7

0 -4

-3

-2

-1

0

1

2

)

3

-1

-2 Modern Humans Neandertals

-3

Broken Hill Australopiths

-4

PC 3 (5.1

)

Fig. 4. Bivariate plot of PC 2 and PC 3 of the log-raw PCA.

4

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616

612

Table 6 Results of the PCA on the log-shape data Principal component 1 2 3 4 5 6 Total

Table 7 Results of the PCA on the log-raw group means

Eigenvalue

% total variance explained

0.00720 0.00206 0.00182 0.00148 0.00123 0.00097

43.3 12.4 10.9 8.9 7.4 5.8

0.01476

Mean group position

PC 2

1 2 3 4 5 6

88.7

PC 3

PC 4

PC 5

Total PC 6

1.591 0.560 0.384 0.259 0.197 0.054 0.120 0.087 0.028 0.023 0.022 0.005 0.333 0.677 0.670 0.083 0.455 0.181 0.886 1.716 0.114 0.006 0.085 0.391

Neandertals Modern humans Broken Hill E.898 Australopiths Loadings

PC 1

PC 1

PC 2

PC 3

PC 4

EB (shape) 0.200* 0.252* 0.480* 0.092 TB (shape) 0.025 0.598* 0.189* 0.331* MTW (shape) 0.024 0.219* 0.049 0.543* LTW (shape) 0.040 0.272* 0.431* 0.435* TW (shape) 0.208* 0.599* 0.449* 0.310* CB (shape) 0.308* 0.337* 0.111 0.792* CAP (shape) 0.109 0.361* 0.066 0.475* CSI (shape) 0.025 0.299* 0.014 0.035 OFML (shape) 0.765* 0.351* 0.230* 0.141** OFSI (shape) 0.684* 0.427* 0.285* 0.035 MP (shape) 0.957* 0.199* 0.165** 0.095 LP (shape) 0.468* 0.256* 0.731* 0.146**

Principal component

PC 5

PC 6

0.015 0.498* 0.334* 0.291* 0.321* 0.029 0.421* 0.382* 0.085 0.370* 0.073 0.358*

0.139** 0.255* 0.199* 0.141** 0.403* 0.120 0.374* 0.342* 0.349* 0.350* 0.041 0.119

*Correlation is significant at the 0.01 level (two-tailed test). **Correlation is significant at the 0.05 level (two-tailed test).

individuals (six Neandertals, 12 EUP, 17 LUP, two Mesolithic, and 25 recent humans) that preserved both measurements. These two measurements are significantly correlated at a ¼ 0.01 with an r-value of 0.60 (Fig. 10). Unfortunately, Churchill et al. (1996) did not use a mediolateral measurement of the olecranon process in their analysis, but it should be

Loadings EB TB MTW LTW TW CB CAP CSI OFML OFSI MP LP

1

PC 1 (43.3 )

-3

-2

0

-1

1

2

3

4

-1

-2 Modern Humans Neandertals Broken Hill Australopiths

-3

-4

PC 2 (12.4

)

Fig. 5. Bivariate plot of PC 1 and PC 2 of the log-shape PCA.

5

54.7 26.6 6.6 4.9 4.6 1.2

0.01448

98.6

PC 3

PC 4

PC 5

PC 6

0.781* 0.796* 0.960* 0.882* 0.850* 0.740* 0.885* 0.930* 0.461 0.585 0.285 0.888*

0.028 0.298 0.002 0.029 0.139 0.419 0.227 0.101 0.353 0.623** 0.951* 0.342

0.480 0.312 0.098 0.284 0.030 0.202 0.082 0.267 0.788* 0.153 0.039 0.039

0.061 0.020 0.192 0.190 0.158 0.462 0.371 0.126 0.127 0.294 0.083 0.147

0.322 0.372 0.006 0.281 0.470 0.009 0.016 0.068 0.137 0.268 0.026 0.010

0.061 0.086 0.112 0.040 0.089 0.084 0.068 0.005 0.017 0.251 0.070 0.232

*Correlation is significant at the 0.01 level (two-tailed test). **Correlation is significant at the 0.05 level (two-tailed test).

positively correlated with OFML and negatively correlated with MP and LP. However, the significant correlation between the two superoinferior measures suggests that, although unassociated African archaic human ulnae and humeri exhibit large olecranon processes and small olecranon fossae, the probability that any single individual possessed both of these characteristics is low. Table 8 Results of the PCA on the log-shape group means

Total

0

0.00804 0.00391 0.00097 0.00072 0.00067 0.00017

PC 2

1 2 3 4 5 6

2

% total variance explained

PC 1

Principal component 3

Eigenvalue

Loadings

Eigenvalue

% total variance explained

0.00393 0.00137 0.00074 0.00071 0.00025 0.00008

54.2 18.8 10.2 9.8 3.5 1.1

0.00708 PC 1

EB (shape) 0.052 TB (shape) 0.496 MTW (shape) 0.151 LTW (shape) 0.040 TW (shape) 0.321 CB (shape) 0.644** CAP (shape) 0.524 CSI (shape) 0.349 OFML (shape) 0.368 OFSI (shape) 0.712** MP (shape) 0.992* LP (shape) 0.621**

97.6

PC 2

PC 3

PC 4

PC 5

PC 6

0.891* 0.622** 0.380 0.537 0.501 0.198 0.369 0.750* 0.830* 0.400 0.028 0.424

0.186 0.246 0.546 0.308 0.704** 0.543 0.446 0.080 0.261 0.000 0.032 0.260

0.142 0.362 0.284 0.717 0.299 0.435 0.520 0.379 0.310 0.455 0.085 0.200

0.177 0.100 0.540 0.065 0.223 0.177 0.252 0.064 0.055 0.308 0.079 0.409

0.267 0.075 0.141 0.284 0.070 0.033 0.036 0.242 0.033 0.074 0.003 0.308

*Correlation is significant at the 0.01 level (two-tailed test). **Correlation is significant at the 0.05 level (two-tailed test).

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616

613

3

Neandertal 2

1

LSA

LUP

EUP PC 1 (54.7

-2

-1

0 Am. White 0 Mesolithic

Peru.

Am. Black 1

)

Broken Hill 2

-1

Australopith

-2

Skhul-Qafzeh PC 2 (26.6 )

Fig. 6. Bivariate plot of PC 1 and PC 2 of the log-raw group-mean PCA.

primitive morphology). Only the modern-like morphology of the Broken Hill humerus would require explanation in this scenario. According to the second scenario, most African archaic humans would look like modern humans in terms of their elbow morphology, as is the case with Broken Hill E.898. Klasies River Mouth, Border Cave, and Baringo would then be outliers [note that Churchill et al. (1996) found some individuals in their modern human samples of ulnae that approximated Neandertals in proximal ulnar morphology]. By this scenario, modern human elbow morphology would be the primitive condition and that seen in the Neandertals a derived condition. This scenario would leave the Neandertal-like morphology of the ulnae from Baringo, Klasies River Mouth, and Border

On the basis of this assumption, the results of our analysis suggest two possible evolutionary scenarios to account for the elbow morphology seen in African archaic humans. In the first scenario, the majority of African archaic humans would possess elbow morphology that is more similar to that of Neandertals than to that of modern humans, as is the case with the Klasies River Mouth, Border Cave, and Baringo ulnae. Broken Hill E.898 would therefore be an outlier and exhibit a much smaller olecranon fossa and presumably a smaller olecranon process than the African archaic mean. By this scenario, modern human elbow morphology would be derived and not even fully present until after anatomically modern humans had emerged as a recognizable species (thus, early modern humans from Klasies River Mouth and Border Cave express the 3

Skhul-Qafzeh

2 Neandertal

1 Mesolithic

-2

-1 Australopith

0 Am. Black 0 Am.White EUP LUP Peru. -1 Broken Hill

-2

PC 3 (6.6

PC 2 (26.6 1

2

LSA

)

Fig. 7. Bivariate plot of PC 2 and PC 3 of the log-raw group-mean PCA.

) 3

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616

614

2

Broken Hill

1

Am. Black Peru.

EUP LUP

Am. White PC 1 (54.2

0

-2

Mesolithic 0

-1

1

2

) 3

LSA Australopith -1

Skhul-Qafzeh Neandertal -2

PC 2 (18.8 )

Fig. 8. Bivariate plot of PC 1 and PC 2 of the log-shape group-mean PCA.

Cave requiring explanation, since archaic and early modern humans from Africa would be expected to display the primitive morphology. Despite the higher number of outliers, this second scenario seems more likely than the first scenario if australopith elbow morphology is considered. The five australopith humeri included in this analysis are morphologically more similar to the modern human sample than to the Neandertal sample, which suggests that modern human distal humeral morphology is primitive and that of the Neandertals is derived (as in the second scenario presented above). If our assumption that olecranon fossa size and olecranon process size positively covary is correct, then modern human proximal ulnar morphology is likely primitive as well. Indeed, like modern humans, australopith and great ape proximal ulnae tend to be characterized by anteroposteriorly and proximodistally short olecranon processes (see Senut, 1981). The morphological similarity in the proximal ulnae of Neandertals, early modern humans from South Africa (Klasies River Mouth and Border Cave), and African archaic humans (Baringo) remains enigmatic. Perhaps functional demands for elbow stability in the context of Middle Stone Age/Middle

Paleolithic hunting and tool-use behaviors resulted in a shift towards the derived (¼ ‘‘archaic’’ in this context) morphology in populations across the Old World. Given that the olecranon process develops from its own secondary center of ossification and that this center fuses in the teen years (Scheuer and Black, 2001), mechanical loads on the elbow experienced in early adulthood may have resulted in epigenetic developmental shifts in proximal ulnar morphology without necessitating change in the alleles controlling development of the elbow. The primitive morphology would again become dominant once functional stresses on the elbow were alleviated and growth of the proximal ulna and distal humerus proceeded unaltered. The sample of middle Pleistocene African humeral and ulnar fragments are probably representative of a variable, possibly transitional, population that contained individuals with small olecranon processes and fossae like most modern humans and individuals with large olecranon processes and fossae like most Neandertals. Variation within Middle Paleolithic hominins appears to have become fixed as between-group variation differentiating Neandertals (who tended to have large

Table 9 Euclidean distances among log-shape group means Group Neandertal Broken Hill Australopith Skh ul-Qafzeh EUP LUP Mesolithic LSA Peruvian Black White

Neandertal

Broken Hill

Australopith

Skhul-Qafzeh

EUP

LUP

Mesolithic

LSA

Peruvian

Black

White

0.000 0.175 0.216 0.244 0.137 0.140 0.176 0.115 0.173 0.179 0.155

0.000 0.130 0.163 0.062 0.054 0.113 0.093 0.056 0.066 0.051

0.000 0.116 0.153 0.140 0.128 0.149 0.103 0.109 0.107

0.000 0.172 0.161 0.148 0.162 0.120 0.130 0.143

0.000 0.041 0.097 0.062 0.067 0.078 0.064

0.000 0.100 0.069 0.058 0.063 0.050

0.000 0.116 0.088 0.092 0.103

0.000 0.087 0.104 0.080

0.000 0.045 0.047

0.000 0.051

0.000

T.R. Yokley, S.E. Churchill / Journal of Human Evolution 51 (2006) 603e616 Neandertal BrokenHill Peruvian Black White EUP LUP LSA Mesolithic Australopith SkhulQafzeh 0.20

0.15

0.10

0.05

0.00

615

(1996) for similar findings with ulnae]. These morphological similarities may be indicative of gene flow or similar behavioral practices (see Trinkaus and Churchill, 1988), but most biological populations tend to exhibit ranges of variation that overlap those of closely related populations. However, the amount of overlap is often difficult to assess, especially among fossil samples. With a population such as middle-to-late Pleistocene African humans, for which an extremely small number of specimens are known, the typical tendency among paleoanthropologists has been to assume that the known fragments are average representatives of the morphology of the individuals within this population, but we must be willing to accept the fact that some fossils represent the morphological extremes of a population and that apparent similarities with other groups may actually be the result of sampling error.

Distance

Conclusions Fig. 9. UPGMA clustering of groups based on Euclidean distances of log-shape group means.

olecranon processes and fossae) from modern humans (who tend to have small olecranon processes and fossae), although both groups remain somewhat variable. The modern human sample used in this analysis actually exhibits a range of variation that encompasses both of these morphological complexes, and it is not unreasonable to assume that other groups might have possessed substantial ranges of variation as well. The results presented here are largely indicative of differences in average group morphology. While these results reveal differences in group position, they also reveal substantial amounts of overlap between most of the groups. In fact, a few modern human humeri actually appear morphologically similar to Neandertals: most of these come from populations that also shared a Stone Age hunting-and-gathering lifestyle [EUP, LUP, and LSA samples; see also Churchill et al.

25 Neandertals EUP LUP Mesolithic Recent Humans

24 23

Olecranon process length

22

The main differences between Neandertal and modern human elbow morphology appear to be related to the size of the olecranon process and fossa. Broken Hill E.898 is morphologically more similar to modern humans than to Neandertals, although it may not be representative of all African archaic humans. African archaic elbow morphology probably exhibits a range of variation that overlaps that of both Neandertals and modern humans, although our present knowledge is hampered by a lack of fossil material. Australopiths are morphologically more similar to modern humans than to Neandertals, which suggests that modern human distal humeral morphology is primitive and that of the Neandertals is derived. However, more research is needed to test this conclusion. The functional basis of the differences revealed in this analysis remains an unresolved issue. A larger olecranon process and fossa may be indicative of habitual joint positions in which the joint is maximally loaded (see Trinkaus and Churchill, 1988) or perhaps simply higher average stresses across the joint during growth. However, more research is needed before the functional significance of these differences can be adequately assessed. Acknowledgements

21

We gratefully thank the many curators that allowed us access to skeletal material in their care. We are also thankful to Chris Vinyard, Bill Jungers, Richard Jantz, and Karen Yokley for statistical advice and discussions and to Chris Vinyard for helpful comments on an early version of this manuscript.

20 19 18 17 16 15

References

14 13 r = 0.60

12 11 13

14

15

16

17

18

19

20

21

22

23

24

Olecranon fossa S-I diameter Fig. 10. Bivariate plot of olecranon fossa S-I diameter and olecranon process S-I length.

Bacon, A.M., 2000. Principal components analysis of distal humeral shape in Pliocene to recent African hominids: the contribution of geometric morphometrics. Am. J. Phys. Anthropol. 111, 479e487. Churchill, S.E., 1994. Human upper body evolution in the Eurasian later Pleistocene. Ph.D. Dissertation, University of New Mexico. Churchill, S.E., Pearson, O.M., Grine, F.E., Trinkaus, E., Holliday, T.W., 1996. Morphological affinities of the proximal ulna from Klasies River main site: archaic or modern? J. Hum. Evol. 31, 213e237.

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