Age of the oldest known Homo sapiens from eastern Africa

Tarsals from the Sima de los Huesos Middle Pleistocene site (Atapuerca, Burgos, Spain)

Here, we provide a complete, updated, and illustrated inventory, as well as a comprehensive study, of the tarsals (rearfoot) recovered from the Middle Pleistocene site of Sima de los Huesos (SH, Atapuerca, Spain) in comparison to other Homo comparative samples, both extant and fossil. The minimum number of individuals (MNI) estimated from the tarsals has been established as 15, which represents 51.7% of the 29 dental individuals identified within the SH sample. Within the SH hominin foot sample, an exclusive combination of primitive or plesiomorphic and derived or autapomorphic traits can be observed when compared with other Homo individuals/populations. Other characters are shared among SH hominins and Neandertals that might represent shared derived or autapomorphic traits for this evolutionary line, and most are likely related to robusticity (e.g., rectangular-like trochlea of the talus, broad calcanei, broad naviculars, and short lateral cuneiforms). Additionally, we observed some exclusive autapomorphic traits in the SH tarsal sample (e.g., narrow head of the talus and short intermediate cuneiforms). A few exclusive traits in SH tarsal remains are even more robust than in Neandertals (e.g., broad lateral malleolar facet in talus, more projected sustentaculum tali, and broad medial cuneiform). These traits could suggest a slightly higher level of gracilization in the tarsal bones of Neandertals compared to the SH sample that is also supported by other anatomical postcranial skeleton elements. Additionally, some paleobiological inferences are made in relation to body size (stature and body mass) and some associations are proposed within the SH sample. In conclusion, the morphology of the SH tarsi confirms an evolutionary relationship of sister groups between this population and Neandertals, probably representing a morphotype similar to the Neandertal ancestors.

Metatarsals and foot phalanges from the Sima de los Huesos Middle Pleistocene site (Atapuerca, Burgos, Spain)

This study provides a complete, updated and illustrated inventory, as well as a comprehensive study, of the metatarsals and foot phalanges (forefoot) recovered from the Middle Pleistocene site of Sima de los Huesos (SH, Atapuerca, Spain) in comparison to other Homo comparative samples, both extant and fossils. This current updated review has established a minimum number of individuals (MNI) of 17, which represent 58.6% of the 29 dental individuals identified within the SH sample. An exclusive or autoapomorphic combination of traits can be recognized within the SH hominin foot sample. A few traits appear primitive or plesiomorphic when compared with earlier Homo individuals and other recent modern humans. There are other metrical and morphological traits that SH hominins and Neandertals have in common that sometimes represent shared derived traits in this evolutionary line, most of which are probably related to robusticity. Furthermore, some exclusive autoapomorphic traits are observed in the SH sample: a very broad first metatarsal, long and broad hallucal proximal foot phalanges and possibly extremely robust lateral distal foot phalanges compared to those of Neandertals and modern humans. In these last traits, the SH metatarsals and pedal phalanges are even more robust than in Neandertals. They are herein named as "hyper-Neandertal" traits, which could suggest a slight gracilization process in this evolutionary line, at least in the hallux toe. Finally, some paleobiological inferences are made in relation to body size (stature and body mass) and some associations are proposed within the SH sample.

Paleolithic eyed needles and the evolution of dress

Eyed needles are among the most iconic of Paleolithic artifacts, traditionally seen as rare indicators of prehistoric clothing, particularly tailoring. However, recent finds across Africa and Eurasia show that other technologies like bone awls also facilitated the creation of fitted garments. Nonetheless, the advent of delicate eyed needles suggests a demand for more refined, efficient sewing. This refinement may signify two major developments: the emergence of underwear in layered garment assemblages, and/or a transition in adornment from body modification to decorating clothes, as humans covered themselves more completely for thermal protection. Archaeological evidence for underwear is limited, but the Upper Paleolithic saw an increase in personal ornaments, some sewn onto clothing. Eyed needles may mark a pivotal shift as clothes acquired the social functions of dress, decoupling clothing from climate and ensuring its enduring presence.

Early warning signals of the termination of the African Humid Period(s)

The transition from a humid green Sahara to today's hyperarid conditions in northern Africa ~5.5 thousand years ago shows the dramatic environmental change to which human societies were exposed and had to adapt to. In this work, we show that in the 620,000-year environmental record from the Chew Bahir basin in the southern Ethiopian Rift, with its decadal resolution, this one thousand year long transition is particularly well documented, along with 20-80 year long droughts, recurring every ~160 years, as possible early warnings. Together with events of extreme wetness at the end of the transition, these droughts form a pronounced climate "flickering", which can be simulated in climate models and is also present in earlier climate transitions in the Chew Bahir environmental record, indicating that transitions with flickering are characteristic of this region.

Quantifying hominin morphological diversity at the end of the middle Pleistocene: Implications for the origin of Homo sapiens

OBJECTIVES

The Middle Pleistocene (MP) saw the emergence of new species of hominins: Homo sapiens in Africa, H. neanderthalensis, and possibly Denisovans in Eurasia, whose most recent common ancestor is thought to have lived in Africa around 600 ka ago. However, hominin remains from this period present a wide range of morphological variation making it difficult to securely determine their taxonomic attribution and their phylogenetic position within the Homo genus. This study proposes to reconsider the phenetic relationships between MP hominin fossils in order to clarify evolutionary trends and contacts between the populations they represent.

MATERIALS AND METHODS

We used a Geometric Morphometrics approach to quantify the morphological variation of the calvarium of controversial MP specimens from Africa and Eurasia by using a comparative sample that can be divided into 5 groups: H. ergaster, H. erectus, H. neanderthalensis, and H. sapiens, as well as individuals from current modern human populations. We performed a Generalized Procrustes Analysis, a Principal Component Analysis, and Multinomial Principal Component Logistic Regressions to determine the phenetic affinities of the controversial Middle Pleistocene specimens with the other groups.

RESULTS

MP African and Eurasian specimens represent several populations, some of which show strong affinities with H. neanderthalensis in Europe or H. sapiens in Africa, others presenting multiple affinities.

DISCUSSION

These MP populations might have contributed to the emergence of these two species in different proportions. This study proposes a new framework for the human evolutionary history during the MP.

Hunter-gatherer genetics research: Importance and avenues

Major developments in the field of genetics in the past few decades have revolutionised notions of what it means to be human. Although currently only a few populations around the world practise a hunting and gathering lifestyle, this mode of subsistence has characterised members of our species since its very origins and allowed us to migrate across the planet. Therefore, the geographical distribution of hunter-gatherer populations, dependence on local ecosystems and connections to past populations and neighbouring groups have provided unique insights into our evolutionary origins. However, given the vulnerable status of hunter-gatherers worldwide, the development of the field of anthropological genetics requires that we reevaluate how we conduct research with these communities. Here, we review how the inclusion of hunter-gatherer populations in genetics studies has advanced our understanding of human origins, ancient population migrations and interactions as well as phenotypic adaptations and adaptability to different environments, and the important scientific and medical applications of these advancements. At the same time, we highlight the necessity to address yet unresolved questions and identify areas in which the field may benefit from improvements.

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.

Concurrent Asian monsoon strengthening and early modern human dispersal to East Asia during the last interglacial

The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)-currently the largest monsoon system-remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy- and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial.

Eurasian back-migration into Northeast Africa was a complex and multifaceted process

Recent studies have identified Northeast Africa as an important area for human movements during the Holocene. Eurasian populations have moved back into Northeastern Africa and contributed to the genetic composition of its people. By gathering the largest reference dataset to date of Northeast, North, and East African as well as Middle Eastern populations, we give new depth to our knowledge of Northeast African demographic history. By employing local ancestry methods, we isolated the Non-African parts of modern-day Northeast African genomes and identified the best putative source populations. Egyptians and Sudanese Copts bore most similarities to Levantine populations whilst other populations in the region generally had predominantly genetic contributions from the Arabian peninsula rather than Levantine populations for their Non-African genetic component. We also date admixture events and investigated which factors influenced the date of admixture and find that major linguistic families were associated with the date of Eurasian admixture. Taken as a whole we detect complex patterns of admixture and diverse origins of Eurasian admixture in Northeast African populations of today.

Human dispersals out of Africa via the Levant

Homo sapiens dispersed from Africa into Eurasia multiple times in the Middle and Late Pleistocene. The route, across northeastern Africa into the Levant, is a viable terrestrial corridor, as the present harsh southern Levant would probably have been savannahs and grasslands during the last interglaciation. Here, we document wetland sediments with luminescence ages falling in the last interglaciation in the southern Levant, showing protracted phases of moisture availability. Wetland sediments in Wadi Gharandal containing Levallois artifacts yielded an age of 84 ka. Our findings support the growing consensus for a well-watered Jordan Rift Valley that funneled migrants into western Asia and northern Arabia.

Endocranial volumes and human evolution

Enlarging brains have been held up as the classic (if not the only) example of a consistent long-term trend in human evolution.  And hominin endocranial volumes certainly expanded four-fold over the subfamily's seven-million-year history, while on a very coarse scale later hominids showed a strong tendency to have larger brains than earlier ones.  However, closer scrutiny of this apparent trend reveals that it was extremely episodic and irregular, a fact that argues against the notion that it was driven by social interactions internal to the hominin clade.  In addition, an overall tendency to brain volume increase was expressed independently and concurrently within at least three separate lineages of the genus Homo - suggesting that, whatever the exact influences were that promoted this global trend, they need to be sought among stimuli that acted comprehensively over the entire vast range of periods, geographies and environments that members of our subfamily occupied.  Significantly, though, the dramatic recent shrinkage of the brain within the species Homo sapiens implies that the emergence of modern human cognition (via the adoption of the symbolic information processing mode, likely driven by the spontaneous invention of language in an exaptively enabled brain) was not the culmination of the overall hominin trend towards brain enlargement, but rather a departure from it.

A weakly structured stem for human origins in Africa

Despite broad agreement that Homo sapiens originated in Africa, considerable uncertainty surrounds specific models of divergence and migration across the continent1. Progress is hampered by a shortage of fossil and genomic data, as well as variability in previous estimates of divergence times1. Here we seek to discriminate among such models by considering linkage disequilibrium and diversity-based statistics, optimized for rapid, complex demographic inference2. We infer detailed demographic models for populations across Africa, including eastern and western representatives, and newly sequenced whole genomes from 44 Nama (Khoe-San) individuals from southern Africa. We infer a reticulated African population history in which present-day population structure dates back to Marine Isotope Stage 5. The earliest population divergence among contemporary populations occurred 120,000 to 135,000 years ago and was preceded by links between two or more weakly differentiated ancestral Homo populations connected by gene flow over hundreds of thousands of years. Such weakly structured stem models explain patterns of polymorphism that had previously been attributed to contributions from archaic hominins in Africa2-7. In contrast to models with archaic introgression, we predict that fossil remains from coexisting ancestral populations should be genetically and morphologically similar, and that only an inferred 1-4% of genetic differentiation among contemporary human populations can be attributed to genetic drift between stem populations. We show that model misspecification explains the variation in previous estimates of divergence times, and argue that studying a range of models is key to making robust inferences about deep history.

Hypercementosis in Late Pleistocene Homo sapiens fossils from Klasies River Main Site, South Africa

OBJECTIVE

To examine early Homo sapiens fossils from the Late Pleistocene site of Klasies River Main Site, South Africa for evidence of hypercementosis. The specimens represent seven adult individuals dated to between 119,000 and 58,000 years ago. These observations are contextualized in relation to the incidences of hypercementosis among recent human populations and fossil human samples and the potential etiologies of hypercementosis.

DESIGN

The fossils were investigated utilizing micro-CT and nano-CT scanning to visualize and measure cementum apposition on permanent incisor, premolar and molar roots. Cementum thickness was measured at mid-root level, and the volume of the cementum sleeve was calculated for the two fossil specimens that display marked hypercementosis.

RESULTS

Two of the fossils display no evidence of cementum hypertrophy. Three exhibit moderate cementum thickening, barely attaining the quantitative threshold for hypercementosis. Two evince marked hypercementosis. One of the Klasies specimens with marked hypercementosis is judged to be an older individual with periapical abscessing. The second specimen is a younger adult, and seemingly similar in age to other Klasies fossils that exhibit only minimal cementum apposition. However, this second specimen exhibits dento-alveolar ankylosis of the premolar and molars.

CONCLUSIONS

These two fossils from Klasies River Main Site provide the earliest manifestation of hypercementosis in Homo sapiens.

Pathogenic Variants Associated with Rare Monogenic Diseases Established in Ancient Neanderthal and Denisovan Genome-Wide Data

Ancient anatomically modern humans (AMHs) encountered other archaic human species, most notably Neanderthals and Denisovans, when they left Africa and spread across Europe and Asia ~60,000 years ago. They interbred with them, and modern human genomes retain DNA inherited from these interbreeding events. High quality (high coverage) ancient human genomes have recently been sequenced allowing for a direct estimation of individual heterozygosity, which has shown that genetic diversity in these archaic human groups was very low, indicating low population sizes. In this study, we analyze ten ancient human genome-wide data, including four sequenced with high-coverage. We screened these ancient genome-wide data for pathogenic mutations associated with monogenic diseases, and established unusual aggregation of pathogenic mutations in individual subjects, including quadruple homozygous cases of pathogenic variants in the PAH gene associated with the condition phenylketonuria in a ~120,000 years old Neanderthal. Such aggregation of pathogenic mutations is extremely rare in contemporary populations, and their existence in ancient humans could be explained by less significant clinical manifestations coupled with small community sizes, leading to higher inbreeding levels. Our results suggest that pathogenic variants associated with rare diseases might be the result of introgression from other archaic human species, and archaic admixture thus could have influenced disease risk in modern humans.

Nutrigenomics in the context of evolution

Nutrigenomics describes the interaction between nutrients and our genome. Since the origin of our species most of these nutrient-gene communication pathways have not changed. However, our genome experienced over the past 50,000 years a number of evolutionary pressures, which are based on the migration to new environments concerning geography and climate, the transition from hunter-gatherers to farmers including the zoonotic transfer of many pathogenic microbes and the rather recent change of societies to a preferentially sedentary lifestyle and the dominance of Western diet. Human populations responded to these challenges not only by specific anthropometric adaptations, such as skin color and body stature, but also through diversity in dietary intake and different resistance to complex diseases like the metabolic syndrome, cancer and immune disorders. The genetic basis of this adaptation process has been investigated by whole genome genotyping and sequencing including that of DNA extracted from ancient bones. In addition to genomic changes, also the programming of epigenomes in pre- and postnatal phases of life has an important contribution to the response to environmental changes. Thus, insight into the variation of our (epi)genome in the context of our individual's risk for developing complex diseases, helps to understand the evolutionary basis how and why we become ill. This review will discuss the relation of diet, modern environment and our (epi)genome including aspects of redox biology. This has numerous implications for the interpretation of the risks for disease and their prevention.

Review: The different adaptive trajectories in Neanderthals and Homo sapiens and their implications for contemporary human physiological variation

Neanderthals are our one of our closest evolutionary cousins, but while they evolved in Eurasia, we (anatomically modern humans, AMH) originated in Africa. This contrasting evolutionary history has led to morphological and genetic distinctions between our species. Neanderthals are characterised by a relatively stocky build, high body mass, proportionally wide bodies and shorter limbs, a bell-shaped ribcage with a wide pelvis, and a long, low cranial vault compared with AMH. Classic readings of Neanderthal morphology link many of these traits to cold climate adaptations, however these interpretations have been questioned and alternative hypotheses including behavioural factors, dietary adaptations, locomotor specialisations, evolutionary history and neutral evolutionary processes have been invoked. Compared with AMH, Neanderthals may have been adapted for strength and power rather than endurance and may have consumed a diet high in animal products. However, reviewing these hypotheses highlights a number of limitations in our understanding of contemporary human physiology and metabolism, including the relationship between climate and morphology in AMH and Neanderthals, physiological limits on protein consumption, and the relationship between gut morphology and diet. As various relevant factors are clearly linked (e.g. diet, behaviour, metabolism, morphology, activity), ultimately a more integrated approach may be needed to fully understand Neanderthal biology. Variation among contemporary AMHs may offer, with caveats, a useful model for understanding the evolution of both Neanderthal and modern human characteristics, which in turn may further deepen our understanding of variability within and between contemporary humans. Neanderthals; Anatomically modern humans; morphology; climate adaptation; power adaptations; metabolism; diet; physiology; endurance running.

Evidence for Earlier Stone Age 'coastal use': The site of Dungo IV, Benguela Province, Angola

The relationship between Earlier Stone Age (ESA) hominins and the southern African coastal environment has been poorly investigated, despite the high concentration of open-air sites in marine and fluvial terraces of the coastal plain from c. 1Ma onward during the Mid-Pleistocene Transition. Southern Africa provides some of the earliest evidence of coastal subsistence strategies since the end of the Middle Pleistocene, during the Middle Stone Age (MSA). These coastal MSA sites showcase the role of coastal environments in the emergence and development of modern human behaviors. Given the high prevalence of coastal ESA sites throughout the region, we seek to question the relationship between hominins and coastal landscapes much earlier in time. In this regard, the +100 m raised beaches of the Benguela Province, Angola, are key areas as they are well-preserved and contain a dense record of prehistoric occupation from the beginning of the Middle Pleistocene, including sites like Dungo, Mormolo, Sombreiro, Macaca and Punta das Vacas. Accordingly, this paper provides a critical review of the coastal ESA record of southern Africa and a detailed presentation of the Dungo IV site, through a qualitative technological analysis coupled with a quantitative inter-site comparison with contemporary southern African coastal plain sites. Through our detailed technological analyses, we highlight the influence of coastal lithological resources on the technical behaviors of hominin groups, and we propose the existence of a "regional adaptive strategy" in a coastal landscape more than 600 000 years ago. Finally, we argue for the integration of coastal landscapes into hominins' territories, suggesting that adaptation to coastal environments is actually a slower process which begins with "territorialization" well before the emergence and development of Homo sapiens.

Evolution of Homo in the Middle and Late Pleistocene

The Middle and Late Pleistocene is arguably the most interesting period in human evolution. This broad period witnessed the evolution of our own lineage, as well as that of our sister taxon, the Neanderthals, and related Denisovans. It is exceptionally rich in both fossil and archaeological remains, and uniquely benefits from insights gained through molecular approaches, such as paleogenetics and paleoproteomics, that are currently not widely applicable in earlier contexts. This wealth of information paints a highly complex picture, often described as 'the Muddle in the Middle,' defying the common adage that 'more evidence is needed' to resolve it. Here we review competing phylogenetic scenarios and the historical and theoretical developments that shaped our approaches to the fossil record, as well as some of the many remaining open questions associated with this period. We propose that advancing our understanding of this critical time requires more than the addition of data and will necessitate a major shift in our conceptual and theoretical framework.

The taxonomic attribution of African hominin postcrania from the Miocene through the Pleistocene: Associations and assumptions

Postcranial bones may provide valuable information about fossil taxa relating to their locomotor habits, manipulative abilities and body sizes. Distinctive features of the postcranial skeleton are sometimes noted in species diagnoses. Although numerous isolated postcranial fossils have become accepted by many workers as belonging to a particular species, it is worthwhile revisiting the evidence for each attribution before including them in comparative samples in relation to the descriptions of new fossils, functional analyses in relation to particular taxa, or in evolutionary contexts. Although some workers eschew the taxonomic attribution of postcranial fossils as being less important (or interesting) than interpreting their functional morphology, it is impossible to consider the evolution of functional anatomy in a taxonomic and phylogenetic vacuum. There are 21 widely recognized hominin taxa that have been described from sites in Africa dated from the Late Miocene to the Middle Pleistocene; postcranial elements have been attributed to 17 of these. The bones that have been thus assigned range from many parts of a skeleton to isolated elements. However, the extent to which postcranial material can be reliably attributed to a specific taxon varies considerably from site to site and species to species, and is often the subject of considerable debate. Here, we review the postcranial remains attributed to African hominin taxa from the Late Miocene to the Middle and Late Pleistocene and place these assignations into categories of reliability. The catalog of attributions presented here may serve as a guide for making taxonomic decisions in the future.

Convergent and divergent neural circuit architectures that support acoustic communication

Vocal communication is used across extant vertebrates, is evolutionarily ancient, and been maintained, in many lineages. Here I review the neural circuit architectures that support intraspecific acoustic signaling in representative anuran, mammalian and avian species as well as two invertebrates, fruit flies and Hawaiian crickets. I focus on hindbrain motor control motifs and their ties to respiratory circuits, expression of receptors for gonadal steroids in motor, sensory, and limbic neurons as well as divergent modalities that evoke vocal responses. Hindbrain and limbic participants in acoustic communication are highly conserved, while forebrain participants have diverged between anurans and mammals, as well as songbirds and rodents. I discuss the roles of natural and sexual selection in driving speciation, as well as exaptation of circuit elements with ancestral roles in respiration, for producing sounds and driving rhythmic vocal features. Recent technical advances in whole brain fMRI across species will enable real time imaging of acoustic signaling partners, tying auditory perception to vocal production.

Merging morphological and genetic evidence to assess hybridization in Western Eurasian late Pleistocene hominins

Previous scientific consensus saw human evolution as defined by adaptive differences (behavioural and/or biological) and the emergence of Homo sapiens as the ultimate replacement of non-modern groups by a modern, adaptively more competitive group. However, recent research has shown that the process underlying our origins was considerably more complex. While archaeological and fossil evidence suggests that behavioural complexity may not be confined to the modern human lineage, recent palaeogenomic work shows that gene flow between distinct lineages (for example, Neanderthals, Denisovans, early H. sapiens) occurred repeatedly in the late Pleistocene, probably contributing elements to our genetic make-up that might have been crucial to our success as a diverse, adaptable species. Following these advances, the prevailing human origins model has shifted from one of near-complete replacement to a more nuanced view of partial replacement with considerable reticulation. Here we provide a brief introduction to the current genetic evidence for hybridization among hominins, its prevalence in, and effects on, comparative mammal groups, and especially how it manifests in the skull. We then explore the degree to which cranial variation seen in the fossil record of late Pleistocene hominins from Western Eurasia corresponds with our current genetic and comparative data. We are especially interested in understanding the degree to which skeletal data can reflect admixture. Our findings indicate some correspondence between these different lines of evidence, flag individual fossils as possibly admixed, and suggest that different cranial regions may preserve hybridization signals differentially. We urge further studies of the phenotype to expand our ability to detect the ways in which migration, interaction and genetic exchange have shaped the human past, beyond what is currently visible with the lens of ancient DNA.

Pleistocene climate variability in eastern Africa influenced hominin evolution

Despite more than half a century of hominin fossil discoveries in eastern Africa, the regional environmental context of hominin evolution and dispersal is not well established due to the lack of continuous palaeoenvironmental records from one of the proven habitats of early human populations, particularly for the Pleistocene epoch. Here we present a 620,000-year environmental record from Chew Bahir, southern Ethiopia, which is proximal to key fossil sites. Our record documents the potential influence of different episodes of climatic variability on hominin biological and cultural transformation. The appearance of high anatomical diversity in hominin groups coincides with long-lasting and relatively stable humid conditions from ~620,000 to 275,000 years bp (episodes 1-6), interrupted by several abrupt and extreme hydroclimate perturbations. A pattern of pronounced climatic cyclicity transformed habitats during episodes 7-9 (~275,000-60,000 years bp), a crucial phase encompassing the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of Homo sapiens in eastern Africa and key human social and cultural innovations. Those accumulative innovations plus the alignment of humid pulses between northeastern Africa and the eastern Mediterranean during high-frequency climate oscillations of episodes 10-12 (~60,000-10,000 years bp) could have facilitated the global dispersal of H. sapiens.

Pan-Africanism vs. single-origin of Homo sapiens: Putting the debate in the light of evolutionary biology

The scenario of Homo sapiens origin/s within Africa has become increasingly complex, with a pan-African perspective currently challenging the long-established single-origin hypothesis. In this paper, we review the lines of evidence employed in support of each model, highlighting inferential limitations and possible terminological misunderstandings. We argue that the metapopulation scenario envisaged by pan-African proponents well describes a mosaic diversification among late Middle Pleistocene groups. However, this does not rule out a major contribution that emerged from a single population where crucial derived features-notably, a globular braincase-appeared as the result of a punctuated, cladogenetic event. Thus, we suggest that a synthesis is possible and propose a scenario that, in our view, better reconciles with consolidated expectations in evolutionary theory. These indicate cladogenesis in allopatry as an ordinary pattern for the origin of a new species, particularly during phases of marked climatic and environmental instability.

The climate and vegetation backdrop to hominin evolution in Africa

The most profound shift in the African hydroclimate of the last 1 million years occurred around 300 thousand years (ka) ago. This change in African hydroclimate is manifest as an east-west change in moisture balance that cannot be fully explained through linkages to high latitude climate systems. The east-west shift is, instead, probably driven by a shift in the tropical Walker Circulation related to sea surface temperature change driven by orbital forcing. Comparing records of past vegetation change, and hominin evolution and development, with this breakpoint in the climate system is challenging owing to the paucity of study sites available and uncertainties regarding the dating of records. Notwithstanding these uncertainties we find that, broadly speaking, both vegetation and hominins change around 300 ka. The vegetative backdrop suggests that relative abundance of vegetative resources shifted from western to eastern Africa, although resources would have persisted across the continent. The climatic and vegetation changes probably provided challenges for hominins and are broadly coincident with the appearance of Homo sapiens (ca 315 ka) and the emergence of Middle Stone Age technology. The concomitant changes in climate, vegetation and hominin evolution suggest that these factors are closely intertwined. This article is part of the theme issue 'Tropical forests in the deep human past'.

A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa

Eastern Africa has played a prominent role in debates about human evolution and dispersal due to the presence of rich archaeological, palaeoanthropological and palaeoenvironmental records. However, substantial disconnects occur between the spatial and temporal resolutions of these data that complicate their integration. Here, we apply high-resolution climatic simulations of two key parameters, mean annual temperature and precipitation, and a biome model, to produce a highly refined characterisation of the environments inhabited during the eastern African Middle Stone Age. Occupations are typically found in sub-humid climates and landscapes dominated by or including tropical xerophytic shrubland. Marked expansions from these core landscapes include movement into hotter, low-altitude landscapes in Marine Isotope Stage 5 and cooler, high-altitude landscapes in Marine Isotope Stage 3, with the recurrent inhabitation of ecotones between open and forested habitats. Through our use of high-resolution climate models, we demonstrate a significant independent relationship between past precipitation and patterns of Middle Stone Age stone tool production modes overlooked by previous studies. Engagement with these models not only enables spatiotemporally explicit examination of climatic variability across Middle Stone Age occupations in eastern Africa but enables clearer characterisation of the habitats early human populations were adapted to, and how they changed through time.

Orbital controls on eastern African hydroclimate in the Pleistocene

Understanding eastern African paleoclimate is critical for contextualizing early human evolution, adaptation, and dispersal, yet Pleistocene climate of this region and its governing mechanisms remain poorly understood due to the lack of long, orbitally-resolved, terrestrial paleoclimate records. Here we present leaf wax hydrogen isotope records of rainfall from paleolake sediment cores from key time windows that resolve long-term trends, variations, and high-latitude effects on tropical African precipitation. Eastern African rainfall was dominantly controlled by variations in low-latitude summer insolation during most of the early and middle Pleistocene, with little evidence that glacial–interglacial cycles impacted rainfall until the late Pleistocene. We observe the influence of high-latitude-driven climate processes emerging from the last interglacial (Marine Isotope Stage 5) to the present, an interval when glacial–interglacial cycles were strong and insolation forcing was weak. Our results demonstrate a variable response of eastern African rainfall to low-latitude insolation forcing and high-latitude-driven climate change, likely related to the relative strengths of these forcings through time and a threshold in monsoon sensitivity. We observe little difference in mean rainfall between the early, middle, and late Pleistocene, which suggests that orbitally-driven climate variations likely played a more significant role than gradual change in the relationship between early humans and their environment.