Smith, T.M. et al. (2007) Earliest evidence of modern human life history in North African early Homo sapiens. Proceedings of the National Academy of Sciences of the USA. 104:6128-6133. (original) (raw)
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Earliest evidence of modern human life history in North African early Homo sapiens
Proceedings of the National Academy of Sciences, 2007
Recent developmental studies demonstrate that early fossil hominins possessed shorter growth periods than living humans, implying disparate life histories. Analyses of incremental features in teeth provide an accurate means of assessing the age at death of developing dentitions, facilitating direct comparisons with fossil and modern humans. It is currently unknown when and where the prolonged modern human developmental condition originated. Here, an application of x-ray synchrotron microtomography reveals that an early Homo sapiens juvenile from Morocco dated at 160,000 years before present displays an equivalent degree of tooth development to modern European children at the same age. Crown formation times in the juvenile's macrodont dentition are higher than modern human mean values, whereas root development is accelerated relative to modern humans but is less than living apes and some fossil hominins. The juvenile from Jebel Irhoud is currently the oldest-known member of Homo with a developmental pattern (degree of eruption, developmental stage, and crown formation time) that is more similar to modern H. sapiens than to earlier members of Homo. This study also underscores the continuing importance of North Africa for understanding the origins of human anatomical and behavioral modernity. Corresponding biological and cultural changes may have appeared relatively late in the course of human evolution. dental development ͉ human evolution ͉ human origins ͉ synchrotron microtomography ͉ tooth growth Author contributions: T.M.S., P.T., and J.-J.H. designed research; T.M.S., P.T., D.J.R., R.G., and S.E. performed research; M.B. and J.-J.H. contributed new reagents/analytic tools; T.M.S., P.T., and D.J.R. analyzed data; and T.M.S., P.T., R.G., S.E., and J.-J.H. wrote the paper. The authors declare no conflict of interest. Freely available online through the PNAS open access option.
The Aterian fossil hominins represent one of the most abundant series of human remains associated with Middle Stone Age/Middle Paleolithic assemblages in Africa. Their dates have been revised and they are now mostly assigned to a period between 90 and 35 ka. Although the Aterian human fossil record is exclusively Moroccan, Aterian assemblages are found throughout a vast geographical area extending to the Western Desert of Egypt. Their makers represent populations that were located close to the main gate to Eurasia and that immediately predated the last out-of-Africa exodus. In this chapter, we present an analysis of the Aterian dental remains. The sizes of the Aterian dentitions are particularly spectacular, especially for the post-canine dentition. This massiveness is reminiscent of the Middle Paleolithic modern humans from the Near East, but also of the early Homo sapiens in North and East Africa. Morphologically, this megadontia is expressed in the development of mass-additive traits. The Aterian dentition also displays relatively thick enamel. These features help to set some of the traits observed in Neandertals in perspective and highlight their primitive or derived nature. The Aterian morphological pattern is also important to consider when interpreting the dental morphology of the first modern humans in Eurasia.
American Journal of Physical Anthropology, 1995
Most analyses of dental enamel hypoplasia compare frequencies of disturbed tooth types, which do not account for variability in the area of affected enamel. An alternate methodology, hypoplastic area, is presented here that accounts for this variability by combining acute and continuous enamel hypoplasia into an interval-level variable. The method compares samples based on individuals, by multiple tooth type variables, or by a single value rather than by tooth types. Use of the hypoplastic area method is illustrated by analyzing human skeletal dentitions in three archaeological samples: Meroitic Nubians from Semna South, Sudan; Anasazi from Navajo Reservoir, New Mexico; and Mogollon from Grasshopper Pueblo, Arizona. Both univariate and multivariate statistical tests are employed to assess variation in defects between individuals and samples. By incorporating measurements of continuous defects, the hypoplastic area method provides information beyond that of frequency data in comparing levels of stress. Flexibility of the method is also discussed. © 1995 Wiley-Liss, Inc.
Proceedings of the …, 2007
The evolution of life history (pace of growth and reproduction) was crucial to ancient hominin adaptations. The study of dental development facilitates assessment of growth and development in fossil hominins with greater precision than other skeletal analyses. During tooth formation, biological rhythms manifest in enamel and dentine, creating a permanent record of growth rate and duration. Quantification of these internal and external incremental features yields developmental benchmarks, including ages at crown completion, tooth eruption, and root completion. Molar eruption is correlated with other aspects of life history. Recent evidence for developmental differences between modern humans and Neanderthals remains ambiguous. By measuring tooth formation in the entire dentition of a juvenile Neanderthal from Scladina, Belgium, we show that most teeth formed over a shorter time than in modern humans and that dental initiation and eruption were relatively advanced. By registering manifestations of stress across the dentition, we are able to present a precise chronology of Neanderthal dental development that differs from modern humans. At 8 years of age at death, this juvenile displays a degree of development comparable with modern human children who are several years older. We suggest that age at death in juvenile Neanderthals should not be assessed by comparison with modern human standards, particularly those derived from populations of European origin. Moreover, evidence from the Scladina juvenile and other similarly aged hominins suggests that a prolonged childhood and slow life history are unique to Homo sapiens.
Dental Ontogeny in Pliocene and Early Pleistocene Hominins
Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the humanlike and ape-like affinities of fossil hominins. Teeth are invaluable for understanding maturation as age at death can be directly assessed from dental microstructure, and dental development has been shown to correlate with life history across primates broadly. We employ non-destructive synchrotron imaging to characterize incremental development, molar emergence, and age at death in more than 20 Australopithecus anamensis, Australopithecus africanus, Paranthropus robustus and South African early Homo juveniles. Long-period line periodicities range from at least 6-12 days (possibly 5-13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo. Crown formation times of australopith and early Homo postcanine teeth fall below or at the low end of extant human values; Paranthropus robustus dentitions have the shortest formation times. Pliocene and early Pleistocene hominins show remarkable variation, and previous reports of age at death that employ a narrow range of estimated long-period line periodicities, cuspal enamel thicknesses, or initiation ages are likely to be in error. New chronological ages for SK 62 and StW 151 are several months younger than previous histological estimates, while Sts 24 is more than one year older. Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa. We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent PLOS ONE |
The Dentition of the Earliest Modern Humans: How 'Modern' Are They
African and Western Asian contemporaries of Neanderthals, generally considered to be the earliest Homo sapiens, are not particularly 'modern' looking in their cranial anatomy. Here we test whether the dental morphological signal agrees with this assessment. We used a Bayesian statistical approach to classifying individuals into 'modern' and 'non-modern' groups based on dental non-metric traits. The classification was based on dental trait frequencies for two 'known' samples of 109 Upper Paleolithic H. sapiens and 129 Neanderthal individuals. A cross-validation test of these individuals correctly classified them 95% of the time. Our early H. sapiens sample included 41 individuals from Southern Africa, Northern Africa and Western Asia. We treated our early H. sapiens individuals as 'unknown' and calculated the probability that each belonged to either the Upper Paleolithic or Neanderthal sample. We hypothesized that if the earliest H. sapiens were already dentally modern, then they would be assigned to the Upper Paleolithic H. sapiens group. We also hypothesized that if there had been significant admixture in Western Asia during the initial dispersal out of Africa, these samples would have the largest proportion of individuals classified as Neanderthal. Our results indicated that the latter was not the case. The smallest proportion of misclassified individuals came from Western Asia (7%) and the highest proportion of misclassified individuals came from Northern Africa (38%). In most cases it appears to be the predominance of primitive features, rather than derived Neanderthal traits that drove the classification. We conclude (1) by the time the earliest H. sapiens dispersed from Africa they had already attained a more-or-less modern dental pattern; (2) in the past, as is the case today, Late Pleistocene Africans were not a homogeneous group, some retained primitive dental traits in higher proportions than others. Furthermore, we acknowledge that while our method is an excellent tool for discriminating between Upper Paleolithic H. sapiens and Neanderthals, it may not be appropriate for testing Neanderthal – H. sapiens admixture because all traits (primitive and derived) are weighed equally. Moreover, to best assess admixture it is likely necessary to incorporate a model for how the traits track population history and/or gene flow.
Anterior tooth growth periods in Neandertals were comparable to those of modern humans
Proceedings of the National Academy of Sciences, 2005
A longstanding controversy in paleoanthropology surrounds the question of whether Neandertals shared the prolonged growth periods of modern humans. To address this question, this investigation compares the duration of enamel formation in Neandertals with that of three comparative modern human groups. Because dental and somatic growth are correlated with each other, dental growth periods are indicative of overall periods of growth. Growth increments on the anterior teeth of Neandertals, modern Inuit, and modern people from Newcastle and southern Africa were counted and their means compared. In addition, potential variation in the time spans represented by growth increments was considered and incorporated into the analysis of enamel formation times. These analyses show that Neandertal imbricational enamel formation times, although likely to have been faster than those of the Inuit, are not likely to have been faster than those of the Newcastle sample and for some teeth are clearly slower than those of the southern African sample. Thus, Neandertal tooth growth and, by extension, somatic growth, appears to be encompassed within the modern human range of interpopulation variation.