Human-like enamel growth in Homo naledi

OBJECTIVES

A modern pattern (rate and duration) of dental development occurs relatively recently during human evolution. Given the temporal overlap of Homo naledi with the first appearance of fossil Homo sapiens in Africa, this small-bodied and small-brained hominin presents an opportunity to elucidate the evolution of enamel growth in the hominin clade. Here we conduct the first histological study of two permanent mandibular canines and one permanent maxillary first molar, representing three individuals attributed to H. naledi. We reconstruct the rate and duration of enamel growth and compare these findings to those reported for other fossil hominins and recent humans.

MATERIALS AND METHODS

Thin sections of each tooth were produced using standard histological methods. Daily and longer period incremental markings were measured to reconstruct enamel secretion and extension rates, Retzius periodicity, canine crown and molar cusp formation time.

RESULTS

Daily enamel secretion rates overlapped with those from recent hominins. Canine crown formation time is similar to that observed in recent Europeans but is longer than canine formation times reported for most other hominins including Australopithecus and H. neanderthalensis. The extended period of canine formation appears to be due to a relatively tall enamel crown and a sustained slow rate of enamel extension in the cervical portion of the crown. A Retzius periodicity of 11 days for the canines, and nine days for the molar, in H. naledi parallel results found in recent humans. An 11-day periodicity has not been reported for Late Pleistocene Homo (H. erectus, H. neanderthalensis) and is rarely found in Australopithecus and Paranthropus species.

DISCUSSION

Enamel growth of H. naledi is most similar to recent humans though comparative data are limited for most fossil hominin species. The high Retzius periodicity values do not follow expectations for a small-brained hominin.

Sex-biased sampling may influence Homo naledi tooth size variation

A frequent source of debate in paleoanthropology concerns the taxonomic unity of fossil assemblages, with many hominin samples exhibiting elevated levels of variation that can be interpreted as indicating the presence of multiple species. By contrast, the large assemblage of hominin fossils from the Rising Star cave system, assigned to Homo naledi, exhibits a remarkably low degree of variation for most skeletal elements. Many factors can contribute to low sample variation, including genetic drift, strong natural selection, biased sex ratios, and sampling of closely related individuals. In this study, we tested for potential sex-biased sampling in the Rising Star dental sample. We compared coefficients of variation for the H. naledi teeth to those for eight extant hominoid samples. We used a resampling procedure that generated samples from the extant taxa that matched the sample size of the fossil sample for each possible Rising Star dental sex ratio. We found that variation at four H. naledi tooth positions-I2, M1, P4, M1-is so low that the possibility that one sex is represented by few or no individuals in the sample cannot be excluded. Additional evidence is needed to corroborate this inference, such as ancient DNA or enamel proteome data, and our study design does not address other potential factors that would account for low sample variation. Nevertheless, our results highlight the importance of considering the taphonomic history of a hominin assemblage and suggest that sex-biased sampling is a plausible explanation for the low level of phenotypic variation found in some aspects of the current H. naledi assemblage.

An examination of Homo naledi early juveniles recovered from the Rising Star cave system, South Africa

BACKGROUND

Six Homo naledi early juveniles were recovered from U.W. 101 (Dinaledi Chamber), U.W. 102 (Lesedi Chamber), and U.W. 110 in the Rising Star cave system.

AIM

This paper develops the information for the H. naledi early juvenile life stage, as defined by a combination of deciduous and permanent dentition, and the eruption of the first permanent molar.

SUBJECTS AND METHODS

The growing number of young individuals recovered from the Rising Star cave system allows us to gain a better understanding of their variation, or lack thereof, and provides a basis to estimate broad ranges for age at death of the individuals. The individuals are identified and described through craniodental remains and spatial associations.

RESULTS AND CONCLUSION

Our results show that the teeth are remarkably consistent across the localities in their metric and non-metric traits, and our analyses refine previous estimations on dental eruptions with the first permanent molar erupting first in the sequence among permanent teeth.

Descriptive catalog of Homo naledi dental remains from the 2013 to 2015 excavations of the Dinaledi Chamber, site U.W. 101, within the Rising Star cave system, South Africa

More than 150 hominin teeth, dated to ∼330-241 thousand years ago, were recovered during the 2013-2015 excavations of the Dinaledi Chamber of the Rising Star cave system, South Africa. These fossils comprise the first large single-site sample of hominin teeth from the Middle Pleistocene of Africa. Though scattered remains attributable to Homo sapiens, or their possible lineal ancestors, are known from older and younger sites across the continent, the distinctive morphological feature set of the Dinaledi teeth supports the recognition of a novel hominin species, Homo naledi. This material provides evidence of African Homo lineage diversity that lasts until at least the Middle Pleistocene. Here, a catalog, anatomical descriptions, and details of preservation and taphonomic alteration are provided for the Dinaledi teeth. Where possible, provisional associations among teeth are also proposed. To facilitate future research, we also provide access to a catalog of surface files of the Rising Star jaws and teeth.

Revisiting the age of the Florisbad hominin material

In 1996, Grün and coworkers provided an ESR age determination for a hominin molar from Florisbad, South Africa, at 259 ± 35 ka. The most anatomically informative hominin specimen from Florisbad is a fragmentary craniofacial specimen, attributed by many to early Homo sapiens, which has been assumed to derive from the same individual as this tooth. Since 1996, evidence about the evolutionary context for the later Middle Pleistocene and its associated hominins in Africa had markedly changed. If the Florisbad date is accurate and if the molar is associated with the craniofacial specimen, this evidence may suggest that Homo naledi coexisted in time and geography with H. sapiens in southern Africa. Thus, the accuracy for all dates needs critical investigation. This study examines the published record of excavation and subsequent analyses for the Florisbad material. We find that the contemporary records raise doubt about the contemporaneity of the tooth and calvaria. The site's complex stratigraphy and the details about the tooth's discovery also pose challenges for the previous ESR age estimate. Because the fragmentary cranial specimen has value for morphological comparisons, developing additional means of understanding its geological age is necessary. The current data do not demonstrate the presence of H. sapiens in southern Africa at ~260 ka.

Kazak mitochondrial genomes provide insights into the human population history of Central Eurasia

As a historical nomadic group in Central Asia, Kazaks have mainly inhabited the steppe zone from the Altay Mountains in the East to the Caspian Sea in the West. Fine scale characterization of the genetic profile and population structure of Kazaks would be invaluable for understanding their population history and modeling prehistoric human expansions across the Eurasian steppes. With this mind, we characterized the maternal lineages of 200 Kazaks from Jetisuu at mitochondrial genome level. Our results reveal that Jetisuu Kazaks have unique mtDNA haplotypes including those belonging to the basal branches of both West Eurasian (R0, H, HV) and East Eurasian (A, B, C, D) lineages. The great diversity observed in their maternal lineages may reflect pivotal geographic location of Kazaks in Eurasia and implies a complex history for this population. Comparative analyses of mitochondrial genomes of human populations in Central Eurasia reveal a common maternal genetic ancestry for Turko-Mongolian speakers and their expansion being responsible for the presence of East Eurasian maternal lineages in Central Eurasia. Our analyses further indicate maternal genetic affinity between the Sherpas from the Tibetan Plateau with the Turko-Mongolian speakers.

Frontal sinuses and human evolution

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species' holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species.

The immature Homo naledi ilium from the Lesedi Chamber, Rising Star Cave, South Africa

Objectives

Homo naledi is represented by abundant remains from the Dinaledi Chamber of the Rising Star Cave system in South Africa. While pelvic elements from the Dinaledi Chamber of the cave are fragmentary, a relatively complete ilium (U.W. 102a–138) was recovered from the Lesedi Chamber. We reconstructed and analyzed the Lesedi ilium, providing qualitative descriptions and quantitative assessment of its morphology and developmental state.

Materials and Methods

We compared the Lesedi ilium to remains from the Dinaledi Chamber, other South African hominin fossils, and an ontogenetic series of human ilia. We used the Dinaledi adults as a guide for reconstructing the Lesedi ilium. To assess development of the Lesedi ilium, we compared immature/mature proportional ilium height for fossils and humans. We used 3D geometric morphometrics (GMs) to examine size and shape variation among this sample.

Results

The Lesedi ilium showed incipient development of features expressed in adult H. naledi ilia. The proportional height of the Lesedi ilium was within the range of human juveniles between 4–11 years of age. GM analyses showed that the Lesedi ilium had an iliac blade shape similar to those of australopiths and an expanded auricular surface more similar to humans.

Conclusions

The reconstructed Lesedi specimen represents the best preserved ilium of H. naledi, confirming the australopith‐like iliac blade morphology first hypothesized in adult specimens, and establishing that this anatomy was present early in this species' ontogeny. In contrast to australopiths, the Lesedi ilium displays an enlarged sacroiliac joint, the significance of which requires further investigation.

Mandibular ramus morphology and species identification in Australopithecus sediba

The site of Malapa, South Africa, has produced fossil evidence from multiple individuals of Australopithecus sediba including the partial skeletons designated as MH1 (holotype) and MH2 (paratype). A recent article in this Journal presented the hypothesis that MH1 and MH2 are not one species but instead represent two different genera: Australopithecus and Homo, respectively. Here we briefly evaluate this claim. We review the evidence from across the skeleton that demonstrates that MH1 and MH2 represent a single species, and we highlight other fossil samples that show the same pattern of mandibular ramus variation as observed in MH1 and MH2. The evidence shows that there is no reason to separate MH1 and MH2 into different species or genera based upon mandibular ramus morphology. This case illustrates how misleading small fragments of anatomy can be, why researchers should not use such fragments particularly for species and genus-level diagnoses, and why it is essential to use all available evidence.

Comment on "A global environmental crisis 42,000 years ago"

Cooper et al. (Research Articles, 19 February 2021, p. 811) propose that a weakening geomagnetic field prior to the Laschamps Excursion explains megafaunal extinctions and human cultural changes that they claim happened 42,000 years ago. However, these authors misrepresent both the data and interpretations of cited work on extinctions and human cultural changes, so the specific claims they make about extinctions and cultural changes are false.

Strategizing public-facing work within an academic career

BACKGROUND

Most anthropological researchers will engage with the public at some stage of their career. Some develop strong skills in public-facing work, building bridges between local and global communities and the scientific enterprise. Anthropology and archaeology are unsustainable without such community support. Yet engagement work often goes unrecognized and unrewarded within academic institutions.

AIMS

We focus on ways to translate the value of public-facing work within academic career trajectories. We consider some of the challenges and benefits of such work for early career researchers and for senior researchers, and we provide guidance that will be helpful across a broad range of career objectives.

MATERIALS AND METHODS

This study employs narratives of both early career and senior anthropologists.

RESULTS

Both early career and senior researchers report challenges and successes in building public-facing work.

DISCUSSION

Pursuing public-facing work in ways that are recognized in academic settings can be challenging both in early career and senior settings. The advice in this paper can help individuals build strategies that will lead to sustainable engagement and career progress.

CONCLUSION

Attaining a balance between research and public engagement benefits both the fields of anthropology and human biology.

Fostering Responsible Research on Ancient DNA

Anticipating and addressing the social implications of scientific work is a fundamental responsibility of all scientists. However, expectations for ethically sound practices can evolve over time as the implications of science come to be better understood. Contemporary researchers who work with ancient human remains, including those who conduct ancient DNA research, face precisely this challenge as it becomes clear that practices such as community engagement are needed to address the important social implications of this work. To foster and promote ethical engagement between researchers and communities, we offer five practical recommendations for ancient DNA researchers: (1) formally consult with communities; (2) address cultural and ethical considerations; (3) engage communities and support capacity building; (4) develop plans to report results and manage data; and (5) develop plans for long-term responsibility and stewardship. Ultimately, every member of a research team has an important role in fostering ethical research on ancient DNA.

Sexual dimorphism of the relationship between the gut and pelvis in humans

OBJECTIVES

Obstetric demands have long been considered in the evolution of the pelvis, yet consideration of the interaction of pregnancy, the pelvis, and the gastrointestinal tract (gut) is lacking. Here, we explore sex differences in the relationship of gut volume with body size and pelvic dimensions.

MATERIALS AND METHODS

Computed tomography (CT) scans of living adult Homo sapiens (46 females and 42 males) were obtained to measure in vivo gut volume (GV) and to extract 3D models of the pelvis. We collected 19 3D landmarks from each pelvis model to acquire pelvic measurements. We used ordinary least squares regression to explore relationships between GV and body weight, stature, and linear pelvic dimensions.

RESULTS

The gut-pelvis relationship differs between males and females. Females do not exhibit significant statistical correlations between GV and any variable tested. GV correlates with body size and pelvic outlet size in males. GV scales with negative allometry relative to body weight, stature, maximum bi-iliac breadth, inferior transverse outlet breadth, and bispinous distance in males.

DISCUSSION

The lack of association between GV and body size in females may be due to limits imposed by the anticipation of accommodating a gravid uterus and/or the increased plasticity of the pelvis. The pattern of relationship between GV and the pelvic outlet suggests the role of the bony pelvis in supporting the adominal viscera in females may be small relative to its role in childbirth. We conclude that gut size inference in fossil hominins from skeletal proxies is limited and confounded by sexual dimorphism.

Evidence for independent peripheral and central age-related hearing impairment

Deleterious age-related changes in the central auditory nervous system have been referred to as central age-related hearing impairment (ARHI) or central presbycusis. Central ARHI is often assumed to be the consequence of peripheral ARHI. However, it is possible that certain aspects of central ARHI are independent from peripheral ARHI. A confirmation of this possibility could lead to significant improvements in current rehabilitation practices. The major difficulty in addressing this issue arises from confounding factors, such as other age-related changes in both the cochlea and central non-auditory brain structures. Because gap detection is a common measure of central auditory temporal processing, and gap detection thresholds are less influenced by changes in other brain functions such as learning and memory, we investigated the potential relationship between age-related peripheral hearing loss (i.e., audiograms) and age-related changes in gap detection. Consistent with previous studies, a significant difference was found for gap detection thresholds between young and older adults. However, among older adults, no significant associations were observed between gap detection ability and several other independent variables including the pure tone audiogram average, the Wechsler Adult Intelligence Scale-Vocabulary score, gender, and age. Statistical analyses showed little or no contributions from these independent variables to gap detection thresholds. Thus, our data indicate that age-related decline in central temporal processing is largely independent of peripheral ARHI.

Immature remains and the first partial skeleton of a juvenile Homo naledi, a late Middle Pleistocene hominin from South Africa

Immature remains are critical for understanding maturational processes in hominin species as well as for interpreting changes in ontogenetic development in hominin evolution. The study of these subjects is hindered by the fact that associated juvenile remains are extremely rare in the hominin fossil record. Here we describe an assemblage of immature remains of Homo naledi recovered from the 2013–2014 excavation season. From this assemblage, we attribute 16 postcranial elements and a partial mandible with some dentition to a single juvenile Homo naledi individual. The find includes postcranial elements never before discovered as immature elements in the sub-equatorial early hominin fossil record, and contributes new data to the field of hominin ontogeny.

Femoral neck and shaft structure in Homo naledi from the Dinaledi Chamber (Rising Star System, South Africa)

The abundant femoral assemblage of Homo naledi found in the Dinaledi Chamber provides a unique opportunity to test hypotheses regarding the taxonomy, locomotion, and loading patterns of this species. Here we describe neck and shaft cross-sectional structure of all the femoral fossils recovered in the Dinaledi Chamber and compare them to a broad sample of fossil hominins, recent humans, and extant apes. Cross-sectional geometric (CSG) properties from the femoral neck (base of neck and midneck) and diaphysis (subtrochanteric region and midshaft) were obtained through CT scans for H. naledi and through CT scans or from the literature for the comparative sample. The comparison of CSG properties of H. naledi and the comparative samples shows that H. naledi femoral neck is quite derived with low superoinferior cortical thickness ratio and high relative cortical area. The neck appears superoinferiorly elongated because of two bony pilasters on its superior surface. Homo naledi femoral shaft shows a relatively thick cortex compared to the other hominins. The subtrochanteric region of the diaphysis is mediolaterally elongated resembling early hominins while the midshaft is anteroposteriorly elongated, indicating high mobility levels. In term of diaphyseal robusticity, the H. naledi femur is more gracile that other hominins and most apes. Homo naledi shows a unique combination of characteristics in its femur that undoubtedly indicate a species committed to terrestrial bipedalism but with a unique loading pattern of the femur possibly consequence of the unique postcranial anatomy of the species.

Morphology of the Homo naledi femora from Lesedi

OBJECTIVES

The femoral remains recovered from the Lesedi Chamber are among the most complete South African fossil hominin femora discovered to date and offer new and valuable insights into the anatomy and variation of the bone in Homo naledi. While the femur is one of the best represented postcranial elements in the H. naledi assemblage from the Dinaledi Chamber, the fragmentary and commingled nature of the Dinaledi femoral remains has impeded the assessment of this element in its complete state.

MATERIALS AND METHODS

Here we analyze and provide descriptions of three new relatively well-preserved femoral specimens of H. naledi from the Lesedi Chamber: U.W. 102a-001, U.W. 102a-003, and U.W. 102a-004. These femora are quantitatively and qualitatively compared to multiple extinct hominin femoral specimens, extant hominid taxa, and, where possible, each other.

RESULTS

The Lesedi femora are morphologically similar to the Dinaledi femora for all overlapping regions, with differences limited to few traits of presently unknown significance. The Lesedi distal femur and mid-diaphysis preserve anatomy previously unidentified or unconfirmed in the species, including an anteroposteriorly expanded midshaft and anteriorly expanded patellar surface. The hypothesis that the Lesedi femoral sample may represent two individuals is supported.

DISCUSSION

The Lesedi femora increase the range of variation of femoral morphology in H. naledi. Newly described features of the diaphysis and distal femur are either taxonomically uninformative or Homo-like. Overall, these three new femora are consistent with previous functional interpretations of the H. naledi lower limb as belonging to a species adapted for long distance walking and, possibly, running.

Homo naledi cranial remains from the Lesedi chamber of the rising star cave system, South Africa

Excavations in the Lesedi Chamber (U.W. 102) of the Rising Star cave system from 2013 to 2015 resulted in the recovery of 131 fossils representing at least three individuals attributed to Homo naledi. Hominin fossils were recovered from three collection areas within the Lesedi Chamber. A partial skull with near complete dentition (LES1) and an associated partial skeleton were recovered from Area 102a, while craniodental remains from two other individuals were recovered from Areas 102b and 102c. Here we present detailed anatomical descriptions and metrical comparisons of the Lesedi Chamber H. naledi craniodental remains that preserve diagnostic morphology. The LES1 skull is a presumed male that is slightly larger in size, and shows greater development of ectocranial structures compared to other H. naledi specimens from the Dinaledi Chamber of the Rising Star cave system. Otherwise the Lesedi fossils are notably similar to the Dinaledi fossils in shape and morphology. The Lesedi fossils also preserve the delicate nasal and lacrimal bones that are otherwise unrecorded in the Dinaledi sample. Limited morphological differences between the Dinaledi and Lesedi Chamber hominin samples provides support for the hypothesis that these two assemblages share a close phyletic relationship.

A comparison of hominin teeth from Lincoln Cave, Sterkfontein L/63, and the Dinaledi Chamber, South Africa

Prior to the recovery of Homo naledi from the Dinaledi Chamber of the Rising Star Cave system, the Middle Pleistocene fossil record in Africa was particularly sparse. With the large sample size now available from Dinaledi, the opportunity exists to reassess taxonomically ambiguous teeth unearthed at the nearby site of Sterkfontein. Teeth recovered from Lincoln Cave South and area L/63 at Sterkfontein have been considered ‘most probably Homo ergaster’ and ‘perhaps Archaic Homo sapiens’, respectively. Given the similarities shared between Lincoln Cave, area L/63, and the Dinaledi Chamber with regard to climatic/geologic depositional context and age, two teeth from the former sites, StW 592 and StW 585 respectively, were compared with corresponding tooth types of H. naledi from the Dinaledi Chamber. The results of our study indicate that the Lincoln Cave and area L/63 teeth are morphologically inconsistent with the variation recognised in the H. naledi teeth. Significance: The similar age and climatic/geologic depositional and post-depositional circumstances at Lincoln Cave South, area L/63 at Sterkfontein and the Dinaledi Chamber, Rising Star raise the possibility that these fossils might represent the same species. The teeth StW 592 and StW 585 are not consistent with the variation evident in the known naledi sample. The results of the study do not add to the question of the existence of at least two species of the genus Homo living in close proximity to each other in South Africa at approximately the same time.

Palaeodemographics of individuals in Dinaledi Chamber using dental remains

Hominin skeletal remains from the Dinaledi Chamber, South Africa, represent a minimum of 15 individuals of the extinct species Homo naledi. We examined the dental material from this sample in order to assess the life-history stages of individuals in the sample, in particular to determine the minimum number of individuals in the sample as a whole, and within each of six age classes. We found evidence of individuals within every age class: infant, early juvenile, late juvenile, subadult, young adult and old adult. The Dinaledi Chamber sample is notable in comparison to other samples of human, chimpanzee and fossil hominins in that it has a relatively high representation of juvenile remains, as compared to infants and adults. With 15 individuals, the sample size presented by the Dinaledi dental material is too small to test the hypothesis of attritional versus catastrophic accumulation. The data here provide a basis for further investigation of individual associations within this commingled assemblage, and provide an important comparative data set as a basis for the consideration of life history in H. naledi and other extinct hominin populations.

Late Australopiths and the Emergence of Homo

New fossil discoveries and new analyses increasingly blur the lines between Australopithecus and Homo, changing scientific ideas about the transition between the two genera. The concept of the genus itself remains an unsettled issue, though recent fossil discoveries and theoretical advances, alongside developments in phylogenetic reconstruction and hypothesis testing, are helping us approach a resolution. A review of the latest discoveries and research reveals that (a) despite the recent recovery of key fossil specimens, the antiquity of the genus Homo remains uncertain; (b) although there exist several australopith candidate ancestors for the genus Homo, there is little consensus about which of these, if any, represents the actual ancestor; and (c) potential convergent evolution (homoplasy) in adaptively significant features in late australopiths and basal members of the Homo clade, combined with probable reticulate evolution, makes it currently impossible to identify the direct ancestor of Homo erectus.

The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of ²²²Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.

DOI:http://dx.doi.org/10.7554/eLife.24231.001

Species of ancient humans and the extinct relatives of our ancestors are typically described from a limited number of fossils. However, this was not the case with Homo naledi. More than 1500 fossils representing at least 15 individuals of this species were unearthed from the Rising Star cave system in South Africa between 2013 and 2014. Found deep underground in the Dinaledi Chamber, the H. naledi fossils are the largest collection of a single species of an ancient human-relative discovered in Africa.

After the discovery was reported, a number of questions still remained. Not least among these questions was: how old were the fossils? The material was undated, and predictions ranged from anywhere between 2 million years old and 100,000 years old. H. naledi shared several traits with the most primitive of our ancient relatives, including its small brain. As a result, many scientists guessed that H. naledi was an old species in our family tree, and possibly one of the earliest species to evolve in the genus Homo.

Now, Dirks et al. – who include many of the researchers who were involved in the discovery of H. naledi – report that the fossils are most likely between 236,000 and 335,000 years old. These dates are based on measuring the concentration of radioactive elements, and the damage caused by these elements (which accumulates over time), in three fossilized teeth, plus surrounding rock and sediments from the cave chamber. Importantly, the most crucial tests were carried out at independent laboratories around the world, and the scientists conducted the tests without knowing the results of the other laboratories. Dirks et al. took these extra steps to make sure that the results obtained were reproducible and unbiased.

The estimated dates are much more recent than many had predicted, and mean that H. naledi was alive at the same time as the earliest members of our own species – which most likely evolved between 300,000 and 200,000 years ago. These new findings demonstrate why it can be unwise to try to predict the age of a fossil based only on its appearance, and emphasize the importance of dating specimens via independent tests. Finally in two related reports, Berger et al. suggest how a primitive-looking species like H. naledi survived more recently than many would have predicted, while Hawks et al. describe the discovery of more H. naledi fossils from a separate chamber in the same cave system.

DOI:http://dx.doi.org/10.7554/eLife.24231.002

New fossil remains of Homo naledi from the Lesedi Chamber, South Africa

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species.

Homo naledi and Pleistocene hominin evolution in subequatorial Africa

New discoveries and dating of fossil remains from the Rising Star cave system, Cradle of Humankind, South Africa, have strong implications for our understanding of Pleistocene human evolution in Africa. Direct dating of Homo naledi fossils from the Dinaledi Chamber (Berger et al., 2015) shows that they were deposited between about 236 ka and 335 ka (Dirks et al., 2017), placing H. naledi in the later Middle Pleistocene. Hawks and colleagues (Hawks et al., 2017) report the discovery of a second chamber within the Rising Star system (Dirks et al., 2015) that contains H. naledi remains. Previously, only large-brained modern humans or their close relatives had been demonstrated to exist at this late time in Africa, but the fossil evidence for any hominins in subequatorial Africa was very sparse. It is now evident that a diversity of hominin lineages existed in this region, with some divergent lineages contributing DNA to living humans and at least H. naledi representing a survivor from the earliest stages of diversification within Homo. The existence of a diverse array of hominins in subequatorial comports with our present knowledge of diversity across other savanna-adapted species, as well as with palaeoclimate and paleoenvironmental data. H. naledi casts the fossil and archaeological records into a new light, as we cannot exclude that this lineage was responsible for the production of Acheulean or Middle Stone Age tool industries.

Celiac disease as a model for the evolution of multifactorial disease in humans

Celiac disease (CD) is a multifactorial chronic inflammatory condition that results in injury of the mucosal lining of the small intestine upon ingestion of wheat gluten and related proteins from barley and rye. Although the exact mechanisms leading to CD are not fully understood, the genetic basis of CD has been relatively well characterized. In this review we briefly review the history of discovery, clinical presentation, pathophysiology, and current understanding of the genetics underlying CD risk. Then, we discuss what is known about the current distribution and evolutionary history of genes underlying CD risk in light of other evolutionary models of disease. Specifically, we conclude that the set of loci underlying CD risk did not cohesively evolve as a response to a single past selection event such as the development of agriculture. Rather, deterministic and stochastic evolutionary processes have both contributed to the present distribution of variation in CD risk loci. Selection has shaped some components of this network, but this selection appears to have occurred at different points in the past. Other parts of the CD risk network have likely arisen due to stochastic processes such as genetic drift.

The hand of Homo naledi

A nearly complete right hand of an adult hominin was recovered from the Rising Star cave system, South Africa. Based on associated hominin material, the bones of this hand are attributed to Homo naledi. This hand reveals a long, robust thumb and derived wrist morphology that is shared with Neandertals and modern humans, and considered adaptive for intensified manual manipulation. However, the finger bones are longer and more curved than in most australopiths, indicating frequent use of the hand during life for strong grasping during locomotor climbing and suspension. These markedly curved digits in combination with an otherwise human-like wrist and palm indicate a significant degree of climbing, despite the derived nature of many aspects of the hand and other regions of the postcranial skeleton in H. naledi.

It is unclear to what extent early hominins were adapted to arboreal climbing. Here, the authors show that the nearly complete hand of H. naledi from South Africa has markedly curved digits and otherwise human-like wrist and palm, which indicates the retention of a significant degree of climbing.

Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

We describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. The chamber was always in the dark zone, and not accessible to non-hominins. Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occurring during/after deposition. Hominins accumulated over time as older laminated mudstone units and sediment along the cave floor were eroded. Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date.

DOI:http://dx.doi.org/10.7554/eLife.09561.001

Modern humans, or Homo sapiens, are now the only living species in their genus. But as recently as 20,000 years ago there were other species that belonged to the genus Homo. Together with modern humans, these extinct human species, our immediate ancestors and their close relatives are collectively referred to as ‘hominins’.

Now, Dirks et al. describe an unusual collection of hominin fossils that were found within the Dinaledi Chamber in the Rising Star cave system in South Africa. The fossils all belong to a newly discovered hominin species called Homo naledi, which is described in a related study by Berger et al. The unearthed fossils are the largest collection of hominin fossils from a single species ever to be discovered in Africa, and include the remains of at least 15 individuals and multiple examples of most of the bones in the skeleton.

Dirks et al. explain that the assemblage from the Dinaledi Chamber is unusual because of the large number of fossils discovered so close together in a single chamber deep within the cave system. It is also unusual that no other large animal remains were found in the chamber, and that the bodies had not been damaged by scavengers or predators. The fossils were excavated from soft clay-rich sediments that had accumulated in the chamber over time; it also appears that the bodies were intact when they arrived in the chamber, and then started to decompose.

Dirks et al. discuss a number of explanations as to how the remains came to rest in the Dinaledi Chamber, which range from whether Homo naledi lived in the caves to whether they were brought in by predators. Most of the evidence obtained so far is largely consistent with these bodies being deliberately disposed of in this single location by the same extinct hominin species. However, a number of other explanations cannot be completely ruled out and further investigation is now needed to uncover the series of events that resulted in this unique collection of hominin fossils.

DOI:http://dx.doi.org/10.7554/eLife.09561.002

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.

Assessing eye orbits as predictors of Neandertal group size

OBJECTIVES

The objective is to investigate the hypothesis that Neandertal eye orbits can predict group size and social cognition as presented by Pearce et al. (Proc R Soc B Biol Sci 280 (2013) 20130168).

MATERIALS AND METHODS

We performed a linear regression of known orbital aperture diameter (OAD), neocortex ratio, and group size among 18 extant diurnal primate species. Our data were derived from Kirk (J Hum Evol 51 (2006) 159-170) and Dunbar (J Hum Evol 22 (1992), 469-493; J Hum Evol 28 (1995) 287-296).

RESULTS

There is a positive correlation between OAD and group size; a positive correlation between neocortex and group size; and a positive correlation between OAD and neocortex size. The strength of the collinearity between OAD and neocortex ratio accounts for any significance of OAD in a model. The model that best accounts for variation in group size is one that includes only neocortex ratio; including OAD does not strengthen the model. OAD accounts for 29 percent of the variation in group size.

DISCUSSION

Larger orbits are correlated with larger group sizes in primates, although not significantly when controlling for neocortex ratio. Moreover, the amount of variation in group size that can be explained by OAD is negligible. The larger orbits of Neandertals compared to the average modern human population do not permit any interpretation of cognitive ability related to group size.