尼安德特人基因组学研究进展

尼安德特人是现代人最近的旁支,也是化石资料最丰富的古人类。在现代人起源问题的争论中,尼安德特人对现代人是否有遗传贡献是一个焦点问题。文章综述了近年来关于尼安德特人线粒体基因组和核基因组的研究进展,初步研究表明尼安德特人可能对现代人有遗传贡献,这引发了人们对现代人起源问题的重新思考。藉尼人基因组研究经验进行的古人类基因组学研究将有望揭开现代人起源的谜团,并丰富进化生物学相关领域的理论体系。     

Do modern humans and Neandertals have different patterns of cranial integration?

Studies of cranial differences between modern humans and Neandertals have identified several characteristics for which the two groups differ in their mean values, the proportional relationships with other traits, or both. However, the limited number of fairly complete Neandertals has hindered investigations into patterns of integration – covariance and correlation among traits – in this fossil group. Here, we use multiple approaches specifically designed to deal with fragmentary fossils to test if metric cranial traits in Neandertals fit modern human patterns of integration. Based on 37 traits collected from a sample of 2524 modern humans from Howells’ data set and 20 Neandertals, we show that overall patterns of cranial integration are significantly different between Neandertals and modern humans. However, at the same time, Neandertals are consistent with a modern human pattern of integration for more than three-quarters of the traits. Additionally, the differences between the predicted and actual values for the deviating traits are rather small, indicating that the differences in integration are subtle. Traits for which Neandertals deviate from modern human integration patterns tend to be found in regions where Neandertals and modern humans are known to also differ in their mean values. We conclude that the evolution of patterns of cranial integration is a cause for caution but also presents an opportunity for understanding cranial differences between modern humans and Neandertals.     

Is human longevity a consequence of cultural change or modern biology?

Increased longevity, expressed as the number of individuals surviving to older adulthood, represents a key way that Upper Paleolithic Europeans differ from earlier European (Neandertal) populations. Here, we address whether longevity increased as a result of cultural/adaptive change in Upper Paleolithic Europe, or whether it was introduced to Europe as a part of modern human biology. We compare the ratio of older to younger adults (OY ratio) in an early modern human sample associated with the Middle Paleolithic from Western Asia with OY ratios of European Upper Paleolithic moderns and penecontemporary Neandertals from the same region. We also compare these Neandertals to European Neandertals. The difference between the OY ratios of modern humans of the Middle and Upper Paleolithic is large and significant, but there is no significant difference between the Neandertals and early modern humans of Western Asia. Longevity for the West Asian Neandertals is significantly more common than for the European Neandertals. We conclude that the increase in adult survivorship associated with the Upper Paleolithic is not a biological attribute of modern humans, but reflects important cultural adaptations promoting the demographic and material representations of modernity.     

No evidence of Neandertal mtDNA contribution to early modern humans

The retrieval of mitochondrial DNA (mtDNA) sequences from four Neandertal fossils from Germany, Russia, and Croatia has demonstrated that these individuals carried closely related mtDNAs that are not found among current humans. However, these results do not definitively resolve the question of a possible Neandertal contribution to the gene pool of modern humans since such a contribution might have been erased by genetic drift or by the continuous influx of modern human DNA into the Neandertal gene pool. A further concern is that if some Neandertals carried mtDNA sequences similar to contemporaneous humans, such sequences may be erroneously regarded as modern contaminations when retrieved from fossils. Here we address these issues by the analysis of 24 Neandertal and 40 early modern human remains. The biomolecular preservation of four Neandertals and of five early modern humans was good enough to suggest the preservation of DNA. All four Neandertals yielded mtDNA sequences similar to those previously determined from Neandertal individuals, whereas none of the five early modern humans contained such mtDNA sequences. In combination with current mtDNA data, this excludes any large genetic contribution by Neandertals to early modern humans, but does not rule out the possibility of a smaller contribution.     

Neandertals,competition, and the origin of modern human behavior in the Levant

The East Mediterranean Levant is a small region, but its paleoanthropological record looms large in debates about the origin of modern humans and the fate of the Neandertals. For most of the twentieth century, the Levantine paleoanthropological record supported models of continuity and evolutionary transition between Neandertals and early modern humans. Recent advances in radiometric dating have challenged these models by reversing the chronological relationship between Levantine Neandertals and early modern humans. This revised chronostratigraphy for Levantine Middle Paleolithic human fossils raises interesting questions about the evolutionary relationship between Neandertals and early modern humans. A reconsideration of this relationship moves us closer to understanding the long delay between the origin of morphologically modern‐looking humans during the Middle Paleolithic (>130 Kyr) and the adaptive radiation of modern humans into Eurasia around the time of the transition from the Middle to Upper Paleolithic (50 to 30 Kyr).     

A uniquely modern human pattern of endocranial development. Insights from a new cranial reconstruction of the Neandertal newborn from Mezmaiskaya

The globular braincase of modern humans is distinct from all fossil human species, including our closest extinct relatives, the Neandertals. Such adult shape differences must ultimately be rooted in different developmental patterns, but it is unclear at which point during ontogeny these group characteristics emerge.Here we compared internal shape changes of the braincase from birth to adulthood in Neandertals (N = 10), modern humans (N = 62), and chimpanzees (N = 62). Incomplete fossil specimens, including the two Neandertal newborns from Le Moustier 2 and Mezmaiskaya, were reconstructed using reference-based estimation methods. We used 3D geometric morphometrics to statistically compare shapes of virtual endocasts extracted from computed-tomographic scans. Throughout the analysis, we kept track of possible uncertainties due to the missing data values and small fossil sample sizes.We find that some aspects of endocranial development are shared by the three species. However, in the first year of life, modern humans depart from this presumably ancestral pattern of development. Newborn Neandertals and newborn modern humans have elongated braincases, and similar endocranial volumes. During a ‘globularization-phase’ modern human endocasts change to the globular shape that is characteristic for Homo sapiens. This phase of early development is unique to modern humans, and absent from chimpanzees and Neandertals.Our results support the notion that Neandertals and modern humans reach comparable adult brain sizes via different developmental pathways. The differences between these two human groups are most prominent directly after birth, a critical phase for cognitive development.     

Diagnostic differences in mandibular P4 shape between Neandertals and anatomically modern humans

This study uses elliptical Fourier analysis to quantify shape differences observed in the P(4) crown of Neandertals and anatomically modern humans. Previously, P(4) shape was assessed qualitatively, and results suggested marked differences between Neandertals and anatomically modern humans (Bailey [2002] New Anat. 269:148-156). The goal of this study was to investigate the P(4) shape in more detail, quantifying it in order to determine its utility for taxonomic classification and phylogenetic analysis. A comparison of mean shapes confirms that the mesiolingual portion of the P(4) is truncated in Neandertals, and that this produces a distinctively asymmetrical P(4). A randomization test confirms that the shape difference between Neandertals and anatomically modern humans is significant. Principal component and discriminant function analyses indicate that the relative size of the lingual portion of the tooth also affects tooth shape, with the lingual portion of the Neandertal P(4) being narrower than that of anatomically modern humans. Classification of P(4) crown shapes using discriminant functions analysis is far from perfect. While 86.4% of the teeth were correctly classified, classification was much better for anatomically modern humans (98.1%) than it was for Neandertals (65%). Fortunately, crown shape is but one of several diagnostic characters of the P(4) crown. P(4) crown asymmetry can be added to the growing list of dental morphological characters distinguishing Neandertals from anatomically modern humans. Moreover, based on a comparison of mean tooth shapes in fossil and recent humans, symmetry, rather than asymmetry, appears to be the primitive state, and the high frequency of P(4) asymmetry is likely derived in Neandertals.     

Unconstrained cranial evolution in Neandertals and modern humans compared to common chimpanzees

A variety of lines of evidence support the idea that neutral evolutionary processes (genetic drift, mutation) have been important in generating cranial differences between Neandertals and modern humans. But how do Neandertals and modern humans compare with other species? And how do these comparisons illuminate the evolutionary processes underlying cranial diversification? To address these questions, we used 27 standard cranial measurements collected on 2524 recent modern humans, 20 Neandertals and 237 common chimpanzees to estimate split times between Neandertals and modern humans, and between Pan troglodytes verus and two other subspecies of common chimpanzee. Consistent with a neutral divergence, the Neandertal versus modern human split-time estimates based on cranial measurements are similar to those based on DNA sequences. By contrast, the common chimpanzee cranial estimates are much lower than DNA-sequence estimates. Apparently, cranial evolution has been unconstrained in Neandertals and modern humans compared with common chimpanzees. Based on these and additional analyses, it appears that cranial differentiation in common chimpanzees has been restricted by stabilizing natural selection. Alternatively, this restriction could be due to genetic and/or developmental constraints on the amount of within-group variance (relative to effective population size) available for genetic drift to act on.     

Did the lateral enamel of Neandertal anterior teeth grow differently from that of modern humans?

The formation of lateral enamel in Neandertal anterior teeth has been the subject of recent studies. When compared to the anterior teeth of modern humans from diverse regions (Point Hope, Alaska; Newcastle upon Tyne, England; southern Africa), Neandertal anterior teeth appear to fall within the modern human range of variation for lateral enamel formation time. However, the lateral enamel growth curves of Neandertals are more linear than those of these modern human samples. Other researchers have found that the lateral enamel growth curves of Neandertals are more linear than those of Upper Paleolithic and Mesolithic modern humans as well. The statistical significance of this apparent difference between Neandertal and modern human lateral enamel growth curves is analyzed here. The more linear Neandertal enamel growth curves result from the smaller percentage of total perikymata located in the cervical halves of their teeth. The percentage of total perikymata in the cervical halves of teeth is therefore compared between the Neandertal sample (n=56 teeth) and each modern human population sample: Inuit (n=65 teeth), southern African (n=114 teeth), and northern European (n=115 teeth). There are 18 such comparisons (6 tooth types, Neandertals vs. each of the three modern human populations). Eighteen additional comparisons are made among the modern human population samples. Statistically significant differences are found for 16 of the 18 Neandertal vs. modern human comparisons but for only two of the 18 modern human comparisons. Statistical analyses repeated for subsamples of less worn teeth show a similar pattern. Because surface curvature is thought to affect perikymata spacing, we also conducted measurements to assess surface curvature in thirty teeth. Our analysis shows that surface curvature is not a factor in this lateral enamel growth difference between Neandertals and modern humans.     

Were neandertal and modern human cranial differences produced by natural selection or genetic drift?

Most evolutionary explanations for cranial differences between Neandertals and modern humans emphasize adaptation by natural selection. Features of the crania of Neandertals could be adaptations to the glacial climate of Pleistocene Europe or to the high mechanical strains produced by habitually using the front teeth as tools, while those of modern humans could be adaptations for articulate speech production. A few researchers have proposed non-adaptive explanations. These stress that isolation between Neandertal and modern human populations would have lead to cranial diversification by genetic drift (chance changes in the frequencies of alleles at genetic loci contributing to variation in cranial morphology). Here we use a variety of statistical tests founded on explicit predictions from quantitative- and population-genetic theory to show that genetic drift can explain cranial differences between Neandertals and modern humans. These tests are based on thirty-seven standard cranial measurements from a sample of 2524 modern humans from 30 populations and 20 Neandertal fossils. As a further test, we compare our results for modern human cranial measurements with those for a genetic dataset consisting of 377 microsatellites typed for a sample of 1056 modern humans from 52 populations. We conclude that rather than requiring special adaptive accounts, Neandertal and modern human crania may simply represent two outcomes from a vast space of random evolutionary possibilities.     

No evidence of Neandertal admixture in the mitochondrial genomes of early European modern humans and contemporary Europeans

Neandertals, the archaic human form documented in Eurasia until 29,000 years ago, share no mitochondrial haplotype with modern Europeans. Whether this means that the two groups were reproductively isolated is controversial, and indeed nuclear data have been interpreted as suggesting that they admixed. We explored the range of demographic parameters that may have generated the observed mitochondrial diversity, simulating 3.0 million genealogies under six models differing as for the relationships among contemporary Europeans, Neandertals, and Upper Palaeolithic European early modern humans (EEMH), who coexisted with Neandertals for millennia. We compared by Approximate Bayesian Computations the simulation results with mitochondrial diversity in 7 Neandertals, 3 EEMH, and 150 opportunely chosen modern Europeans. A model of genealogical continuity between EEMH and contemporary Europeans, with no Neandertal contribution, received overwhelming support from the analyses. The maximum degree of Neandertal admixture, under the model of gene flow supported by nuclear data, was estimated at 1.5%, but this model proved 20-32 times less likely than a model without any gene flow. Nuclear and mitochondrial evidence might be reconciled if smaller population sizes led to faster lineage sorting for mitochondrial DNA, and Neandertals shared a longer period of common ancestry with the non-African's than with the African's ancestors.     

The human cranial remains from Gran Dolina Lower Pleistocene site (Sierra de Atapuerca, Spain).

In this article we study the cranial remains of the late Lower Pleistocene human fossils from Gran Dolina (Sierra de Atapuerca, Spain), assigned to the new species Homo antecessor. The cranial remains belong to at least five individuals, both juveniles and adults. The most outstanding feature is the totally modern human morphology of the very complete face ATD6-69, representing the earliest occurrence of the modern face in the fossil record. The Gran Dolina fossils show in the face a suite of modern human apomorphies not found in earlier hominids nor in contemporary or earlier Homo erectus fossils. There are also traits in the Gran Dolina fossils shared with both Neandertals and modern humans, which reinforce the hypothesis that Neandertals and modern humans form a clade, and that the Gran Dolina fossils are a common ancestor to both lineages.     

Revisiting dental fluctuating asymmetry in neandertals and modern humans

Previous studies have suggested that Neandertals experienced greater physiological stress and/or were less capable of mitigating stress than most prehistoric modern human populations. The current study compares estimates of dental fluctuating asymmetry (DFA) for prehistoric Inupiat from Point Hope Alaska, the Late Archaic, and Protohistoric periods from Ohio and West Virginia, and a modern sample from Ohio to Neandertals from Europe and Southwest Asia. DFA results from developmental perturbation during crown formation and is thus an indicator of developmental stress, which previous studies have found to be higher in Neandertals than in several modern human populations. Here, we use recent methodological improvements in the analysis of fluctuating asymmetry suggested by Palmer and Strobeck (Annu Rev Ecol Syst 17 ( 1986 ) 391–421, Developmental instability: causes and consequences ( 2003a ) v.1–v.36, Developmental instability: causes and consequences ( 2003b ) 279–319) and compare the fit of Neandertal DFA Index values with those of modern humans. DFA estimates for each of the modern population samples exceeded measurement error, with the Inupiat exhibiting the highest levels of DFA for most tooth positions. All significant Neandertal z‐scores were positive, exceeding the estimates for each of the modern prehistoric groups. Neandertals exhibited the fewest significant differences from the Inupiat (9.2% of values are significant at P < 0.05), while for the other modern prehistoric groups more than 10% of the Neandertal z‐scores are significant at P < 0.05, more than 90% of these significant scores at P < 0.01. These results suggest that the Inupiat experienced greater developmental stress than the other prehistoric population samples, and that Neandertals were under greater developmental stress than all other prehistoric modern human samples. Am J Phys Anthropol 149:193–204, 2012. © 2012 Wiley Periodicals, Inc.     

Brief communication: The distribution of perikymata on Qafzeh anterior teeth

Recent studies have suggested that Neandertals and modern humans differ in the distribution of perikymata (enamel growth increments) over their permanent anterior tooth crowns. In modern humans, perikymata become increasingly more compact toward the cervix than they do in Neandertals. Previous studies have suggested that a more homogeneous distribution of perikymata, like that of Neandertals, characterizes the anterior teeth of Homo heidelbergensis and Homo erectus as well. Here, we investigated whether Qafzeh anterior teeth (N = 14) differ from those of modern southern Africans, northern Europeans, and Alaskans (N = 47–74 depending on tooth type) in the percentage of perikymata present in their cervical halves. Using the normally distributed modern human values for each tooth type, we calculated Z‐scores for the 14 Qafzeh teeth. All but two of the 14 Qafzeh teeth had negative Z‐scores, meaning that values equal to these would be found in the bottom 50% of the modern human samples. Seven of the 14 would be found in the lowest 5% of the modern human distribution. Qafzeh teeth therefore appear to differ from those of modern humans in the same direction that Neandertals do: with generally lower percentages of perikymata in their cervical regions. The similarity between them appears to represent the retention of a perikymata distribution pattern present in earlier members of the genus Homo, but not generally characteristic of modern humans from diverse regions of the world. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Thoracic morphology in Near Eastern Neandertals and early modern humans compared with recent modern humans from high and low altitudes

Paleoanthropologists have long noted the unique "hyper-barrel-shaped" Neandertal thorax as inferred from fragmentary ribs, clavicles, and sterna. Yet scholars disagree whether the Neandertal thorax represents an adaptation to cold climates or elevated activity levels. Given the difficulties of reconstructing overall chest shape from isolated and fragmentary thoracic skeletal elements, it is worthwhile comparing Neandertals and contemporaneous early modern human fossils from the same geographic region to recent modern human skeletons that are known to have enlarged chests. This study compares thoracic skeletal morphology in two Near Eastern Neandertals (Tabūn C1 and Shanidar 3) and two early modern humans from the same region (Skhūl IV and V) with four samples of recent modern human skeletons from the Andes (n=347): two coastal groups and two groups from high altitudes. The two highland groups, similar to their living descendants, exhibit morphological evidence of anteroposteriorly deep and mediolaterally wide chests as part of respiratory adaptations to high-altitude hypoxia. I calculated the percentage of deviation of each Neandertal and early modern human fossil from the means of the four recent modern human samples for clavicle and rib lengths and curvatures. Shanidar 3 and Tabūn C1 exhibit ribs that are slightly larger and less curved than the Andean samples, indicating slightly larger thoracic skeletons than modern humans who are known to have enlarged chests in response to increased respiratory demands. Skhūl IV and V have significantly shorter ribs with greater curvature suggesting especially narrow thoracic skeletons. Comparisons with Andean populations suggest that the enlarged thoraces of Neandertals may reflect high activity levels, although results from this study do not exclude cold adaptation as an explanatory factor.     

A modern human humerus from the early aurignacian of Vogelherdhöhle (Stetten, Germany)

Implicit in much of the discussion of the cultural and population biological dynamics of modern human origins in Europe is the assumption that the Aurignacian, from its very start, was made by fully modern humans. The veracity of this assumption has been challenged in recent years by the association of Neandertal skeletal remains with a possibly Aurignacian assemblage at Vindija Cave (Croatia) and the association of Neandertals with distinctly Upper Paleolithic (but non-Aurignacian) assemblages at Arcy-sur-Cure and St. C?esaire (France). Ideally we need human fossil material that can be confidently assigned to the early Aurignacian to resolve this issue, yet in reality there is a paucity of well-provenanced human fossils from early Upper Paleolithic contexts. One specimen, a right humerus from the site of Vogelherd (Germany), has been argued, based on its size, robusticity, and muscularity, to possibly represent a Neandertal in an Aurignacian context. The morphological affinities of the Vogelherd humerus were explored by univariate and multivariate comparisons of humeral epiphyseal and diaphyseal shape and strength measures relative to humeri of Neandertals and Early Upper Paleolithic (later Aurignacian and Gravettian) modern humans. On the basis of diaphyseal cross-sectional geometry, deltoid tuberosity morphology, and distal epiphyseal morphology, the specimen falls clearly and consistently with European early modern humans and not with Neandertals. Along with the other Vogelherd human remains, the Vogelherd humerus represents an unequivocal association between the Aurignacian and modern human morphology in Europe.     

Who made the Aurignacian and other early Upper Paleolithic industries?

The Aurignacian is typically taken as a marker of the spread of anatomically modern humans into Europe. However, human remains associated with this industry are frustratingly sparse and often limited to teeth. Some have suggested that Neandertals may, in fact, be responsible for the Aurignacian and the earliest Upper Paleolithic industries. Although dental remains are frequently considered to be taxonomically undiagnostic in this context, recent research shows that Neandertals possess a distinct dental pattern relative to anatomically modern humans. Even so, it is rare to find mandibles or maxillae that preserve all or most of their teeth; and, the probability of correctly identifying individuals represented by only a few teeth or a single tooth is unknown. We present a Bayesian statistical approach to classifying individuals represented exclusively by teeth into two possible groups. The classification is based on dental trait frequencies and sample sizes for ‘known’ samples of 95 Neandertals and 63 Upper Paleolithic modern humans. In a cross validation test of the known samples, 89% of the Neandertals and 89% of the Upper Paleolithic modern humans were classified correctly. We then classified an ‘unknown’ sample of 52 individuals: 34 associated with Aurignacian or other (non-Châtelperronian) early Upper Paleolithic industries, 15 associated with the Châtelperronian, and three unassociated. Of the 34 early Upper Paleolithic-associated individuals, 29 were assigned to modern humans, which is well within the range expected (95% of the time 26-33) with an 11% misclassification rate for an entirely modern human sample. These results provide some of the strongest evidence that anatomically modern humans made the Aurignacian and other (non-Châtelperronian) early Upper Paleolithic industries.     

The effects of distal limb segment shortening on locomotor efficiency in sloped terrain: implications for Neandertal locomotor behavior

Past studies of human locomotor efficiency focused on movement over flat surfaces and concluded that Neandertals were less efficient than modern humans due to a truncated limb morphology, which may have developed to aid thermoregulation in cold climates. However, it is not clear whether this potential locomotor disadvantage would also exist in nonflat terrain. This issue takes on added importance since Neandertals likely spent a significant proportion of their locomotor schedule on sloped, mountainous terrains in the Eurasian landscape. Here a model is developed that determines the relationship between lower limb segment lengths, terrain slope, excursion angle at the hip, and step length. The model is applied to Neandertal and modern human lower limb reconstructions. In addition, for a further independent test that also allows more climateterrain cross comparisons, the same model is applied to bovids living in different terrains and climates. Results indicate that: (1) Neandertals, despite exhibiting shorter lower limbs, would have been able to use similar stride frequencies per speed as longer-limbed modern humans on sloped terrain, due to their lower crural indices; and (2) shortened distal limb segments are characteristic of bovids that inhabit more rugged terrains, regardless of climate. These results suggest that the shortened distal lower limb segments of Neandertals were not a locomotor disadvantage within more rugged environments.