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«The evolution of non-metric dental variation in Europe Shara E. Bailey Department of Anthropology, New York University 25 Waverly Place, New York, NY ...»

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9

Mitteilungen der Gesellschaft für Urgeschichte — 15 (2006)

The evolution

of non-metric dental variation in Europe

Shara E. Bailey

Department of Anthropology, New York University

25 Waverly Place, New York, NY 10012

sbailey@nyu.edu

Max Planck Institute for Evolutionary Anthropology

Deutscher Platz 6, D-04103 Leipzig

Abstract: The potential for dental morphology to answer questions about human evolution in the Middle

to Late Pleistocene has only recently begun to be appreciated. Non-metric dental traits provide useful information for taxonomic diagnosis as well as for assessing biological relationships among living and ancient populations. This study uses dental morphology to assess temporal change in Europe. Homo erectus serves as the presumptive primitive condition for later humans and change over time is assessed by calculating estimates of divergence between groups based on the mean measure of divergence multivariate statistic. The samples include Homo erectus (n = 12), early modern humans from Africa and West Asia (n = 12), early Neandertals (n = 16), late Neandertals (n = 20), Upper Paleolithic Europeans (n = 28) and contemporary Europeans (n = 47). The results show a marked disruption in continuity from early modern to later modern humans when Neandertals are incorporated into the temporal sequence. If Neandertals are left out of the sequence the change in divergence values conforms to expectations for gradual evolution toward the modern human condition (e.g., distance values get progressively smaller through time). At minimum this should set to rest any idea that modern Europeans evolved directly from Neandertal ancestors. Late Neandertals are somewhat less ‘specialized’ than early Neandertals; the implications of this finding are discussed.

Keywords: Neandertals, Dental morphology, Teeth, Modern humans, Middle Paleolithic, Upper Paleolithic, Modern human origins.

Die Entwicklung nicht-metrischer Zahnvariation in Europa Zusammenfassung: Während die Zahnmorphologie schon seit längerer Zeit herangezogen wird, um Aussagen über die Evolution früher Menschenformen zu gewinnen, wird ihr Aussagepotential bei Fragen nach der Evolution der Menschen vom Mittelpleistozän bis in das Jungpleistozän, d.h. von Homo erectus bis zum frühen Homo sapiens, sowie bei Fragen nach ihren Beziehungen zueinander erst seit Kurzem ansatzweise gewürdigt. Besonders Untersuchungen an Neandertalern beschränkten sich in der Vergangenheit im Wesentlichen auf die Merkmale am Schädel und am postkranialen Skelett. Wurden Neandertalerzähne mit einbezogen, lag das Schwergewicht meist auf metrischen Merkmalen. Inzwischen wird deutlich, dass uns auch nicht-metrische Zahnmerkmale nützliche Informationen sowohl für taxonomische Analysen als auch zur Feststellung biologischer Beziehungen zwischen lebenden und früheren Populationen liefern.

Der vorliegende Beitrag verwendet die Zahnmorphologie, um Veränderungen im Laufe der Zeiten in Europa festzustellen. Es wird gezeigt, dass man mittels nicht-metrischer zahnmorphologischer Merkmale in der Lage ist, im Allgemeinen verschiedene Taxa voneinander zu unterscheiden, oder, im Speziellen, Neandertalerzähne von Zähnen moderner Menschen (und denen anderer Menschen). Von besonderer Bedeutung ist diese Frage gerade deshalb, weil Zähne oft die einzigen erhaltenen Menschenreste sind und somit die einzigen Anhaltspunkte für die Zuweisung einer Fundstelle zu einer bestimmten Menschenform bieten. Einige der Merkmale, die in der Untersuchung eine besondere Rolle spielen, sind die Zahl, Anordnung und Ausprägung der Zahnhöcker der Backenzähne und Vorbackenzähne, die Ausprägung der Backenzahnfurchen sowie die schaufelförmige Ausprägung der oberen Schneidezähne. Die Verhältnisse bei Homo erectus dienen bei der Untersuchung als mutmaßliche Ausgangsverhältnisse für die Entwicklungen bei späteren Menschen, und Veränderungen durch die Zeit werden durch Errechnen von Schätzwerten für die Verschiedenheit zwischen Gruppen mittels komplexer statistischer Methoden ermittelt. Die untersuchte Stichprobe umfasst Homo erectus (12 Individuen), frühe moderne Menschen aus Afrika und Westasien (12 Individuen), frühe Neandertaler (16 Individuen), späte Neandertaler (20 Individuen), jungpaläolithische Europäer (28 Individuen) und zeitgenössische Europäer (47 Individuen).

10 Shara E. Bailey Geht man von der Stichprobe der zeitgenössischen Europäer aus, so zeigt sich die größte Übereinstimmung mit den jungpaläolithischen Europäern, die zweitgrößte mit den frühen modernen Menschen, die drittgrößte mit Homo erectus. Die größten Unterschiede bestehen zu den frühen und späten Neandertalern. Ausgehend von den jungpaläolithischen Europäern sind ebenfalls die Übereinstimmungen mit den zeitgnössischen Europäern sowie mit Homo erectus und den frühen modernen Menschen relativ groß, während sich gegenüber den frühen und späten Neandertalern erneut große Unterschiede zeigen. Die frühen modernen Menschen sind in Bezug auf die Zahnmorphologie Homo erectus am ähnlichsten, gefolgt von den Jungpaläolithikern sowie, mit größerem Abstand, den zeitgenössischen Europäern und schließlich, mit noch größerem Abstand, den Neandertalern. Homo erectus ist den frühen modernen Menschen am ähnlichsten, gefolgt von den Jungpaläolithikern. Mit großem Abstand folgen die zeitgenössischen Europäer und die späten Neandertaler, während die größten Abweichungen zu den frühen Neandertalern bestehen. Sowohl die frühen als auch die späten Neandertaler sind am wenigsten verschieden von Homo erectus, gefolgt von den frühen modernen Menschen und den Jungpaläolithikern. Die größten Unterschiede bestehen zu den zeitgenössischen Europäern. In jedem Falle sind die Neandertaler, sowohl die frühen als auch die späten, stets die am weitesten von jeder der anderen Gruppen entfernte Gruppe. Die Unterschiede in der Zahnmorphologie zwischen Neandertalern und den anderen Gruppen nehmen im Laufe der Zeit zu, wobei die späten Neandertaler etwas weniger entfernt von den anderen Gruppen, d.h. etwas weniger ‚spezialisiert’ sind als die frühen Neandertaler. Fasst man die Einzelergebnisse zusammen, so zeigt sich eine deutliche Unterbrechung in der Kontinuität von frühen zu späten modernen Menschen, wenn die Neandertaler in die zeitliche Abfolge integriert werden. Wenn man die Neandertaler nicht berücksichtigt, entspricht die Änderung im Maß der Verschiedenheit den Erwartungen an eine graduelle Evolution hin zu den Verhältnissen beim modernen Menschen. Dieses Ergebnis widerspricht dem Gedanken, dass die modernen Europäer direkt aus den Neandertalern hervorgegangen seien. Einiges spricht dafür, in den Neandertalern und den modernen Menschen unterschiedliche Arten zu sehen, doch bedarf es weiterer Untersuchungen an zusätzlichen Fossilien frühjungpaläolithischer moderner Menschen, um das Verhältnis zwischen Neandertalern und modernen Menschen besser verstehen zu können.





Schlagwörter: Neandertaler, Zahnmorphologie, Zähne, Moderne Menschen, Mittelpaläolithikum, Jungpaläolithikum, Ursprung moderner Menschen Introduction Teeth are durable structures that preserve very well in the archaeological and fossil record. Dental anthropologists have long appreciated teeth for what they can tell us about the lives of past peoples. Pathological conditions (e.g., periodontal disease, caries) can provide information on health, diet and even social status of individuals (Cucina and Tiesler 2003; Eshed et al. 2006; Hillson 1979). Dental eruption status can provide information on age of death of juveniles and macroscopic tooth wear can provide information on age of death of adults (e.g., Brothwell 1981; Smith 1991). Microscopic tooth wear provides information on what an individual was eating close to the time of its death (Teaford and Lytle 1996). Finally, forensic anthropologists have long used teeth to help identify individuals (Pretty and Sweet 2001).

Paleoanthropologists, too, have long appreciated teeth for the important information they can provide about human evolution. For the most part, efforts have concentrated on issues involving earlier hominins, such as the implications of canine size and dimorphism for behavior and social structure of early hominins (e.g., Plavcan and van Schaik 1997). Tooth wear, size and morphology also have provided important information on the diets of early hominins (e.g., Ungar and Grine 1991; Wood and Strait 2004); and tooth morphology has been even used to work out early hominin phylogeny (e.g., Grine 1985;

Strait and Grine 2004).

Comparatively little research has made use of dental morphological variation to investigate questions about the evolution of, and relationships among, later humans (Homo erectus through early Homo sapiens). Studies of Neandertals, in particular, have focused The evolution of non-metric dental variation in Europe primarily on cranial and post-cranial skeletal anatomy (Bookstein et al. 1999; Holliday 1997; Hublin 1978; Rosenberg 1988; Smith 1984; Trinkaus 1981). Until recently, those Neandertal studies that have utilized the dentition have focused mainly on tooth size and the trend for dental reduction during the Later Pleistocene (e.g., Brace et al. 1987).

There are a number of ways in which dental morphology can be used to answer important questions about the later stages of human evolution (i.e., during the Middle and Late Pleistocene). To begin, one must answer a very basic question: In the absence of other material, can teeth, alone, be used to identify taxa? Or more specifically: Can we distinguish Neandertal teeth from those of modern humans (and other hominins)? Once this has been established, changes in dental morphology across space and time can be used to answer microevolutionary questions, specifically: Do we observe evolution towards the modern human condition in particular areas of the world? and/or: Do we see evidence of admixture (gene flow) between archaic and modern humans? Finally, dental morphology may also be used to address the taxonomic status of a hominin. With regard to Neandertals the question is: Were Neandertals a species distinct from Homo sapiens?

Not surprisingly, these last two questions are linked. If Neandertals were simply a geographic variant of Homo sapiens that contributed extensively to the modern human gene pool we would expect to see either (a) gradual evolution from archaic (e.g., Neandertal) to the modern human condition in Europe or (b) evidence of admixture between Neandertals and the earliest modern Europeans (e.g., Upper Paleolithic). If, on the other hand, Neandertals were a species distinct from Homo sapiens then we would expect to see different evolutionary trajectories in the Homo sapiens and Homo neanderthalensis lineages. Moreover, if Neandertals were a species distinct from Homo sapiens interbreeding the two would have been trivial, at best, and most likely limited to sterile hybrids.

As a result, we should see no particularly close relationship between Neandertals and Upper Paleolithic Europeans.

In this paper I will first review the potential of using teeth as a resource for identifying fragmentary human remains. From this foundation, I will then address the second and third questions regarding the microevolution in the later Pleistocene of Europe and what this means for the specific status of Neandertals.

Using teeth to identify Neandertals One of the first steps in any analysis of fossil hominins must be correctly identifying the taxonomic group to which a fossil belongs. Based on dates for the early Aurignacian (presumably made by anatomically modern humans: Bailey and Hublin 2005), and dates for some of the last Neandertals (Higham et al. 2006; Hublin et al. 1995), there was a period of some 3,000 to 5,000 years in which Neandertals and modern humans overlapped in Europe after 35,000 BP. It is likely that the two groups were also coeval in the Levant some kyr ago (McDermott et al. 1993). Therefore, human fossils found dating to these periods of overlap could potentially belong to more than one hominin taxonomic group. While it would be convenient if paleoanthropologists always had complete skeletons, skulls or even complete dentitions with which to work, this is rarely the case. More often than not, what are uncorered in archaeological excavations are isolated teeth or perhaps a few teeth still preserved in a jaw. For this reason, one of the most useful applications of dental morphology to human evolutionary study is being able to identify taxa from fragmentary remains.

12 Shara E. Bailey My research has focused on dental morphological variation in Neandertals and modern humans. It began with a basic question: Are Neandertal teeth qualitatively and quantitatively different from those of modern humans? In the first couple of decades following Darwin’s publication of the Origin of Species (Darwin 1859) paleoanthropologists were mainly concerned with establishing a link between fossil hominins and humans.

The primary goal of many of these studies was to determine whether a fossil was human-like or ape-like (see, for example, Weidenreich 1937; in this publication on the fossils from Zhoukoudian, comparisons were made with humans and apes). Although researchers recognized that Neandertal teeth were clearly different in some respects from those of modern humans (Gorjanović-Kramberger 1906), under this paradigm (i.e., Is it ape-like or is it human-like?) Neandertals were interpreted as having human-like teeth, thus establishing a closer affinity to humans rather than apes (Boule and Vallois 1957). There were those who felt that the morphological eccentricities of Neandertal teeth (e.g., taurodont molars with prismatic roots; see Figure 1) and skull suggested that they were, in fact, different species (e.g., Keith 1913). Nonetheless, until recently it is the first interpretation of Neandertal teeth (that there are no diagnostic differences) that has been more widely accepted (Henry-Gambier et al. 2004; Smith 1976).

Fig. 1: An example of a taurodont Neandertal molar from Krapina, Croatia (left) and a non-taurodont modern human molar from Les Rois, France (right). Taurodont refers to the enlarged pulp chamber housed by the roots that are joined near their apicies. Scale is 5mm.

The evolution of non-metric dental variation in Europe Fig. 2: Unusual Neandertal incisor morphology from the Krapina site. The combination of marked shoveling (A), lingual tubercles (B) and labial convexity (C) is distinctive in Neandertals.



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