ENDURANCE RUNNING AND ITS RELEVANCE TO SCAVENGING BY EARLY HOMININS

It has been argued that endurance running ability may have been important in hominin evolution, giving hominins an enhanced ability to scavenge by allowing them to reach carcasses before other terrestrial vertebrate scavengers. This would have allowed them to exploit the carcass before eventually surrendering it on the arrival of potentially dangerous large terrestrial scavengers. Here, we use a simple spatial model to evaluate the ability of competitors to hominin scavengers to find carcasses. We argue that both hominin and nonhominin terrestrial scavengers would often first have been alerted to available carcasses by overflying aerial scavengers. Our model estimates that nonhominin scavengers will generally be able to reach the carcass within 30 min of detecting a plume of vultures above a nearby carcass. We argue that endurance running over periods greater than 30 min would not have provided a selective advantage to early hominins through increased scavenging opportunities. However, shorter distance running may have been selected, particularly if hominins could defend or usurp carcasses from other mammalian scavengers.     

The metabolic cost of walking in humans, chimpanzees, and early hominins

Bipedalism is a defining feature of the hominin lineage, but the nature and efficiency of early hominin walking remains the focus of much debate. Here, we investigate walking cost in early hominins using experimental data from humans and chimpanzees. We use gait and energetics data from humans, and from chimpanzees walking bipedally and quadrupedally, to test a new model linking locomotor anatomy and posture to walking cost. We then use this model to reconstruct locomotor cost for early, ape-like hominins and for the A.L. 288 Australopithecus afarensis specimen. Results of the model indicate that hind limb length, posture (effective mechanical advantage), and muscle fascicle length contribute nearly equally to differences in walking cost between humans and chimpanzees. Further, relatively small changes in these variables would decrease the cost of bipedalism in an early chimpanzee-like biped below that of quadrupedal apes. Estimates of walking cost in A.L. 288, over a range of hypothetical postures from crouched to fully extended, are below those of quadrupedal apes, but above those of modern humans. These results indicate that walking cost in early hominins was likely similar to or below that of their quadrupedal ape-like forebears, and that by the mid-Pliocene, hominin walking was less costly than that of other apes. This supports the hypothesis that locomotor energy economy was an important evolutionary pressure on hominin bipedalism.     

Adaptation to bipedal gait and fifth metatarsal structural properties in Australopithecus,Paranthropus, and Homo

Humans, unlike African apes, have relatively robust fifth metatarsals (Mt5) presumably reflecting substantial weight-bearing and stability function in the lateral column of the former. When this morphological difference emerged during hominin evolution is debated. Here we investigate internal diaphyseal structure of Mt5s attributed to Australopithecus (from Sterkfontein), Paranthropus (from Swartkrans), and Homo (from Olduvai, Dmanisi, and Dinaledi) placed in the context of human and African ape Mt5 internal diaphyseal structure. ‘Whole-shaft’ properties were evaluated from 17 cross sections sampling 25% to 75% diaphyseal length using computed tomography. To assess structural patterns, scaled cortical bone thicknesses (sCBT) and scaled second moments of area (sSMA) were visualized and evaluated through penalized discriminant analyses. While the majority of fossil hominin Mt5s exhibited ape-like sCBT, their sSMA were comparatively more human-like. Human-like functional loading of the lateral column existed in at least some fossil hominins, although perhaps surprisingly not in hominins from Dmanisi or Dinaledi.     

Subocclusal dental morphology of sahelanthropus tchadensis and the evolution of teeth in hominins

The evolution of the teeth in hominins is characterized by, among other characters, major changes in root morphology. However, little is known of the evolution from a plesiomorphic, ape‐like root morphology to the crown hominin morphology. Here we present a study of the root morphology of the Miocene Chadian hominin Sahelanthropus tchadensis and its comparison to other hominins. The morphology of the whole lower dentition (I₁–M₃) was investigated and described. The comparison with the species Ardipithecus kaddaba and Ardipithecus ramidus indicates a global homogeneity of root morphology in early hominins. This morphology, characterized notably by a reduction of the size and number of the roots of premolars, is a composite between an ape‐like morphology and the later hominin morphology. Trends for root evolution in hominins are proposed, including the transition from a basal hominoid to extant Homo sapiens. This study also illustrates the low association between the evolution of tooth root morphology and the evolution of crowns in hominins. Am J Phys Anthropol 153:116–123, 2014. © 2013 Wiley Periodicals, Inc.     

The Laetoli footprints and early hominin locomotor kinematics

A critical question in human evolution is whether the earliest bipeds walked with a bent-hip, bent-knee gait or on more extended hindlimbs. The differences between these gaits are not trivial, because the adoption of either has important implications for the evolution of bipedalism. In this study, we re-examined the Laetoli footprints to determine whether they can provide information on the locomotor posture of early hominins. Previous researchers have suggested that the stride lengths of Laetoli hominins fall within the range of modern human stride lengths and therefore, Laetoli hominins walked with modern-human-like kinematics. Using a dynamic-similarity analysis, we compared Laetoli hominin stride lengths with those of both modern humans and chimpanzees. Our results indicate that Laetoli hominins could have used either a bent-hip, bent-knee gait, similar to a chimpanzee, or an extended-hindlimb gait, similar to a human. In fact, our data suggest that the Laetoli hominins could have walked near their preferred speeds using either limb posture. This result contrasts with most previous studies, which suggest relatively slow walking speeds for these early bipeds. Despite the many attempts to discern limb-joint kinematics from Laetoli stride lengths, our study concludes that stride lengths alone do not resolve the debate over early hominin locomotor postures.     

Stretching the time span of hominin evolution at Kromdraai (Gauteng,South Africa): Recent discoveries

The Plio-Pleistocene locality of Kromdraai B has yielded the type specimen of Paranthropus robustus, as well as 27 additional fossil hominin specimens. In a number of both cranial and dental features, the states shown by the Kromdraai Paranthropus are more conservative when compared to the more derived conditions displayed by both South African conspecifics and the post-2.3 Ma eastern African Paranthropus boisei. Since 2014, we excavated the earliest known infilling of the Kromdraai cave system in a previously unexplored area. This new locality provided as yet 2200 identifiable macrovertebrate fossils, including 22 hominins, all tied in the earliest part of the stratigraphic sequence, representing three distinct depositional periods. Since we report here, for the first time, the occurrence of fossil hominins in Members 1 and 2, our discoveries stretch the time span of hominin evolution at Kromdraai and contribute to a better understanding of the origin of Paranthropus in southern Africa.     

Bayesian analysis of a morphological supermatrix sheds light on controversial fossil hominin relationships

The phylogenetic relationships of several hominin species remain controversial. Two methodological issues contribute to the uncertainty—use of partial, inconsistent datasets and reliance on phylogenetic methods that are ill-suited to testing competing hypotheses. Here, we report a study designed to overcome these issues. We first compiled a supermatrix of craniodental characters for all widely accepted hominin species. We then took advantage of recently developed Bayesian methods for building trees of serially sampled tips to test among hypotheses that have been put forward in three of the most important current debates in hominin phylogenetics—the relationship between Australopithecus sediba and Homo, the taxonomic status of the Dmanisi hominins, and the place of the so-called hobbit fossils from Flores, Indonesia, in the hominin tree. Based on our results, several published hypotheses can be statistically rejected. For example, the data do not support the claim that Dmanisi hominins and all other early Homo specimens represent a single species, nor that the hobbit fossils are the remains of small-bodied modern humans, one of whom had Down syndrome. More broadly, our study provides a new baseline dataset for future work on hominin phylogeny and illustrates the promise of Bayesian approaches for understanding hominin phylogenetic relationships.     

中更新世晚期中国古人类化石的形态多样性及其演化意义

近年对许家窑、许昌、华龙洞、澎湖、夏河、哈尔滨等人类化石开展的系统研究,引发了学界对中更新世晚期人类演化及分类的不同认识。基于对相关中国人类化石形态特征的分析,作者提出这一时期中国人类化石形态特征表现为四种类型：1）以中更新世晚期人类共有特征为主;2）以原始特征为主;3）以现代特征为主;4）独特形态组合。多数化石形态特征表现为前三种类型,而许昌和许家窑这种以硕大的头骨和巨大颅容量构成的独特形态组合在其他同时期化石还没有发现。化石形态的多样性提示,不同类型的中更新世晚期中国古人类对现代人的形成贡献不同。作者认为在该时期的人类化石形态多样性规律还未阐明的情况下,将具有混合或镶嵌特征的相关人类化石归入分类地位不确定的人群较为合适。     

Reconstructing the Diet of an Extinct Hominin Taxon: The Role of Extant Primate Models

Modern humans represent the only surviving species of an otherwise extinct clade of primates, the hominins. As the closest living relatives to extinct hominins, extant primates are an important source of comparative information for the reconstruction of the diets of extinct hominins. Methods such as comparative and functional morphology, finite element analysis, dental wear, dental topographic analysis, and stable isotope biogeochemistry must be validated and tested within extant populations before they can be applied to extinct taxa. Here we review how these methods have and might be used to reconstruct the diet of a particular extinct hominin, Paranthropus boisei, which has no extant analogue for its highly derived masticatory morphology. Our review emphasizes the potential and limitations of using extant primates as models for the reconstruction of extinct hominin diets. We encourage paleoanthropologists and those who study the feeding behaviors of extant primates to work together to investigate and validate methods for interpreting the diets of all extinct primates, including hominins.     

Early hominin speciation at the Plio/Pleistocene transition

Over the last half-decade or so, there has been an explosion in the recognition of hominin genera and species. We now have the late Miocene genera Orrorin and Sahelanthropus, the mid Pliocene genus Kenyanthropus, three new Pliocene species of Australopithecus (A. anamensis, A. garhi and A. bahrelghazali) and a sub species of Ardipithecus (Ar. r. kadabba) to contend with. Excepting also the more traditional species allocated to Paranthropus, Australopithecus and early Homo we are approaching around 15 species over 5 million years (excluding hominin evolution over the last one million years). Can such a large number of hominin species be justified? An examination of extant hominid (Gorilla gorilla, Pan troglodytes, and Pan paniscus) anatomical variability indicates that the range of fossil hominin variability supports the recognition of this large number of fossil species. It is also shown that not all hominins are directly related to the emergence of early Homo and as such have become extinct. Indeed the traditional australopithecine species 'A'. anamensis, 'A'. afarensis and 'A'. garhi are considered here to belong to a distinct genus Praeanthropus. They are also argued not be hominins, but rather an as yet undefined hominid group from which the more derived hominins evolved. The first hominin is represented by A. africanus or a hominin very much like it. The Paranthropus clade is defined by a derived heterochronic condition of peramorphosis, associated with sequential progenesis (contraction of successive growth stages) in brain and dental development, but a mixture of peramorphic and paedomorphic features in its craniofacial anatomy. Conversely, Kenyanthropus and Homo both share a pattern of peramorphosis, associated with sequential hypermorphosis (prolongation of successive growth stages) in brain development, and paedomorphosis processes in cranial, facial and dental development. This suggests, that these two clades share an important synapomorphy not recognised in the parsimony analyses, suggesting that they may form a sister group relationship to the exclusion of Paranthropus. This highlights the need to re-interpret phylogenetic results in terms of function and development. The rapid speciation and extinction as argued here is in keeping with other fossil groups in Africa at the Plio/Pleistocene transition. This emphasises that we must approach the pre-australopithecines and hominins as part of the endemic African fauna, and not in isolation to the evolutionary and climatic processes that were operating all around them.     

Relevance of aquatic environments for hominins: a case study from Trinil (Java, Indonesia)

Knowledge about dietary niche is key to understanding hominin evolution, since diet influences body proportions, brain size, cognition, and habitat preference. In this study we provide ecological context for the current debate on modernity (or not) of aquatic resource exploitation by hominins. We use the Homo erectus site of Trinil as a case study to investigate how research questions on possible dietary relevance of aquatic environments can be addressed. Faunal and geochemical analysis of aquatic fossils from Trinil Hauptknochenschicht (HK) fauna demonstrate that Trinil at ∼1.5 Ma contained near-coastal rivers, lakes, swamp forests, lagoons, and marshes with minor marine influence, laterally grading into grasslands. Trinil HK environments yielded at least eleven edible mollusc species and four edible fish species that could be procured with no or minimal technology. We demonstrate that, from an ecological point of view, the default assumption should be that omnivorous hominins in coastal habitats with catchable aquatic fauna could have consumed aquatic resources. The hypothesis of aquatic exploitation can be tested with taphonomic analysis of aquatic fossils associated with hominin fossils. We show that midden-like characteristics of large bivalve shell assemblages containing Pseudodon and Elongaria from Trinil HK indicate deliberate collection by a selective agent, possibly hominin.     

Early Human Speciation,Brain Expansion and Dispersal Influenced by African Climate Pulses

Early human evolution is characterised by pulsed speciation and dispersal events that cannot be explained fully by global or continental paleoclimate records. We propose that the collated record of ephemeral East African Rift System (EARS) lakes could be a proxy for the regional paleoclimate conditions experienced by early hominins. Here we show that the presence of these lakes is associated with low levels of dust deposition in both West African and Mediterranean records, but is not associated with long-term global cooling and aridification of East Africa. Hominin expansion and diversification seem to be associated with climate pulses characterized by the precession-forced appearance and disappearance of deep EARS lakes. The most profound period for hominin evolution occurs at about 1.9 Ma; with the highest recorded diversity of hominin species, the appearance of Homo (sensu stricto) and major dispersal events out of East Africa into Eurasia. During this period, ephemeral deep-freshwater lakes appeared along the whole length of the EARS, fundamentally changing the local environment. The relationship between the local environment and hominin brain expansion is less clear. The major step-wise expansion in brain size around 1.9 Ma when Homo appeared was coeval with the occurrence of ephemeral deep lakes. Subsequent incremental increases in brain size are associated with dry periods with few if any lakes. Plio-Pleistocene East African climate pulses as evinced by the paleo-lake records seem, therefore, fundamental to hominin speciation, encephalisation and migration.     

Language, gesture, skill: the co-evolutionary foundations of language

This paper defends a gestural origins hypothesis about the evolution of enhanced communication and language in the hominin lineage. The paper shows that we can develop an incremental model of language evolution on that hypothesis, but not if we suppose that language originated in an expansion of great ape vocalization. On the basis of the gestural origins hypothesis, the paper then advances solutions to four classic problems about the evolution of language: (i) why did language evolve only in the hominin lineage? (ii) why is language use an evolutionarily stable form of informational cooperation, despite the fact that hominins have diverging evolutionary interests? (iii) how did stimulus independent symbols emerge? (iv) what were the origins of complex, syntactically organized symbols? The paper concludes by confronting two challenges: those of testability and of explaining the gesture-to-speech transition; crucial issues for any gestural origins hypothesis.     

Retrieving chronological age from dental remains of early fossil hominins to reconstruct human growth in the past

A chronology of dental development in Pan troglodytes is arguably the best available model with which to compare and contrast reconstructed dental chronologies of the earliest fossil hominins. Establishing a time scale for growth is a requirement for being able to make further comparative observations about timing and rate during both dento-skeletal growth and brain growth. The absolute timing of anterior tooth crown and root formation appears not to reflect the period of somatic growth. In contrast, the molar dentition best reflects changes to the total growth period. Earlier initiation of molar mineralization, shorter crown formation times, less root length formed at gingival emergence into functional occlusion are cumulatively expressed as earlier ages at molar eruption. Things that are similar in modern humans and Pan, such as the total length of time taken to form individual teeth, raise expectations that these would also have been the same in fossil hominins. The best evidence there is from the youngest fossil hominin specimens suggests a close resemblance to the model for Pan but also hints that Gorilla may be a better developmental model for some. A mosaic of great ape-like features currently best describes the timing of early hominin dental development.     

Hominin teeth from the early Late Pleistocene site of Xujiayao,Northern China

It is generally accepted that from the late Middle to the early Late Pleistocene (～340–90 ka BP), Neanderthals were occupying Europe and Western Asia, whereas anatomically modern humans were present in the African continent. In contrast, the paucity of hominin fossil evidence from East Asia from this period impedes a complete evolutionary picture of the genus Homo, as well as assessment of the possible contribution of or interaction with Asian hominins in the evolution of Homo sapiens and Homo neanderthalensis. Here we present a comparative study of a hominin dental sample recovered from the Xujiayao site, in Northern China, attributed to the early Late Pleistocene (MIS 5 to 4). Our dental study reveals a mosaic of primitive and derived dental features for the Xujiayao hominins that can be summarized as follows: i) they are different from archaic and recent modern humans, ii) they present some features that are common but not exclusive to the Neanderthal lineage, and iii) they retain some primitive conformations classically found in East Asian Early and Middle Pleistocene hominins despite their young geological age. Thus, our study evinces the existence in China of a population of unclear taxonomic status with regard to other contemporary populations such as H. sapiens and H. neanderthalensis. The morphological and metric studies of the Xujiayao teeth expand the variability known for early Late Pleistocene hominin fossils and suggest the possibility that a primitive hominin lineage may have survived late into the Late Pleistocene in China. Am J Phys Anthropol 156:224–240, 2015. © 2014 Wiley Periodicals, Inc.     

Forty years on and still going strong: the use of hominin-cercopithecid comparisons in palaeoanthropology

Hominin-cercopithecid comparisons have been used in palaeoanthropology for over forty years. Fossil cercopithecids can be used as a 'control group' to contextualize the adaptations and evolutionary trends of hominins. Observations made on modern cercopithecids can also be applied to questions about human evolution. This article reviews the history of hominin-cercopithecid comparisons, assesses the strengths and weaknesses of cercopithecids as comparators in studies of human evolution, and uses cercopithecid models to explore hominin inter-specific dynamics. Cercopithecids appear to be excellent ecological referents, but may be less good when considering the cognitive abilities and cultural adaptations of hominins. Comparison of cercopithecid and hominin adaptations at Koobi Fora in East Africa indicates that, whereas the cercopithecids were largely grass- or leaf-eating, the hominins occupied a generalist niche, apparently excluding other primate generalist-frugivores. If any of the hominin species at Koobi Fora were sympatric, analogies with modern cercopithecids suggest that inter-specific contact cannot be discounted and may even have been beneficial.     

Variations and asymmetries in regional brain surface in the genus Homo

Paleoneurology is an important field of research within human evolution studies. Variations in size and shape of an endocast help to differentiate among fossil hominin species whereas endocranial asymmetries are related to behavior and cognitive function. Here we analyse variations of the surface of the frontal, parieto-temporal and occipital lobes among different species of Homo, including 39 fossil hominins, ten fossil anatomically modern Homo sapiens and 100 endocasts of extant modern humans. We also test for the possible asymmetries of these features in a large sample of modern humans and observe individual particularities in the fossil specimens.This study contributes important new information about the brain evolution in the genus Homo. Our results show that the general pattern of surface asymmetry for the different regional brain surfaces in fossil species of Homo does not seem to be different from the pattern described in a large sample of anatomically modern H. sapiens, i.e., the right hemisphere has a larger surface than the left, as do the right frontal, the right parieto-temporal and the left occipital lobes compared with the contra-lateral side. It also appears that Asian Homo erectus specimens are discriminated from all other samples of Homo, including African and Georgian specimens that are also sometimes included in that taxon. The Asian fossils show a significantly smaller relative size of the parietal and temporal lobes. Neandertals and anatomically modern H. sapiens, who share the largest endocranial volume of all hominins, show differences when considering the relative contribution of the frontal, parieto-temporal and occipital lobes. These results illustrate an original variation in the pattern of brain organization in hominins independent of variations in total size. The globularization of the brain and the enlargement of the parietal lobes could be considered derived features observed uniquely in anatomically modern H. sapiens.     

Genome digging: insight into the mitochondrial genome of Homo

Background

A fraction of the Neanderthal mitochondrial genome sequence has a similarity with a 5,839-bp nuclear DNA sequence of mitochondrial origin (numt) on the human chromosome 1. This fact has never been interpreted. Although this phenomenon may be attributed to contamination and mosaic assembly of Neanderthal mtDNA from short sequencing reads, we explain the mysterious similarity by integration of this numt (mtAncestor-1) into the nuclear genome of the common ancestor of Neanderthals and modern humans not long before their reproductive split.

Principal Findings

Exploiting bioinformatics, we uncovered an additional numt (mtAncestor-2) with a high similarity to the Neanderthal mtDNA and indicated that both numts represent almost identical replicas of the mtDNA sequences ancestral to the mitochondrial genomes of Neanderthals and modern humans. In the proteins, encoded by mtDNA, the majority of amino acids distinguishing chimpanzees from humans and Neanderthals were acquired by the ancestral hominins. The overall rate of nonsynonymous evolution in Neanderthal mitochondrial protein-coding genes is not higher than in other lineages. The model incorporating the ancestral hominin mtDNA sequences estimates the average divergence age of the mtDNAs of Neanderthals and modern humans to be 450,000–485,000 years. The mtAncestor-1 and mtAncestor-2 sequences were incorporated into the nuclear genome approximately 620,000 years and 2,885,000 years ago, respectively.

Conclusions

This study provides the first insight into the evolution of the mitochondrial DNA in hominins ancestral to Neanderthals and humans. We hypothesize that mtAncestor-1 and mtAncestor-2 are likely to be molecular fossils of the mtDNAs of Homo heidelbergensis and a stem Homo lineage. The d_N/d_S dynamics suggests that the effective population size of extinct hominins was low. However, the hominin lineage ancestral to humans, Neanderthals and H. heidelbergensis, had a larger effective population size and possessed genetic diversity comparable with those of chimpanzee and gorilla.     

Locomotor anatomy and biomechanics of the Dmanisi hominins

The Dmanisi hominins inhabited a northern temperate habitat in the southern Caucasus, approximately 1.8 million years ago. This is the oldest population of hominins known outside of Africa. Understanding the set of anatomical and behavioral traits that equipped this population to exploit their seasonal habitat successfully may shed light on the selection pressures shaping early members of the genus Homo and the ecological strategies that permitted the expansion of their range outside of the African subtropics. The abundant stone tools at the site, as well as taphonomic evidence for butchery, suggest that the Dmanisi hominins were active hunters or scavengers. In this study, we examine the locomotor mechanics of the Dmanisi hind limb to test the hypothesis that the inclusion of meat in the diet is associated with an increase in walking and running economy and endurance. Using comparative data from modern humans, chimpanzees, and gorillas, as well as other fossil hominins, we show that the Dmanisi hind limb was functionally similar to modern humans, with a longitudinal plantar arch, increased limb length, and human-like ankle morphology. Other aspects of the foot, specifically metatarsal morphology and tibial torsion, are less derived and similar to earlier hominins. These results are consistent with hypotheses linking hunting and scavenging to improved walking and running performance in early Homo. Primitive retentions in the Dmanisi foot suggest that locomotor evolution continued through the early Pleistocene.     

Brief Communication: Lumbar lordosis in extinct hominins: Implications of the pelvic incidence

Recently, interest has peaked regarding the posture of extinct hominins. Here, we present a new method of reconstructing lordosis angles of extinct hominin specimens based on pelvic morphology, more specifically the orientation of the sacrum in relation to the acetabulum (pelvic incidence). Two regression models based on the correlation between pelvic incidence and lordosis angle in living hominoids have been developed. The mean values of the calculated lordosis angles based on these models are 36°?45° for australopithecines, 45°?47° for Homo erectus, 27°?34° for the Neandertals and the Sima de los Huesos hominins, and 49°?51° for fossil H. sapiens. The newly calculated lordosis values are consistent with previously published values of extinct hominins (Been et al.: Am J Phys Anthropol 147 (2012) 64–77). If the mean values of the present nonhuman hominoids are representative of the pelvic and lumbar morphology of the last common ancestor between humans and nonhuman hominoids, then both pelvic incidence and lordosis angle dramatically increased during hominin evolution from 27° ± 5 to 22° ± 3 (respectively) in nonhuman hominoids to 54° ± 10 and 51° ± 11 in modern humans. This change to a more human‐like configuration appeared early in the hominin evolution as the pelvis and spines of both australopithecines and H. erectus show a higher pelvic incidence and lordosis angle than nonhuman hominoids. The Sima de los Huesos hominins and Neandertals show a derived configuration with a low pelvic incidence and lordosis angle. Am J Phys Anthropol 154:307–314, 2014. © 2014 Wiley Periodicals, Inc.