The extended neural architecture of human attachment: An fMRI coordinate-based meta-analysis of affiliative studies

Functional imaging studies and clinical evidence indicate that cortical areas relevant to social cognition are closely integrated with evolutionarily conserved basal forebrain structures and neighboring regions, enabling human attachment and affiliative emotions. The neural circuitry of human affiliation is continually being unraveled as functional magnetic resonance imaging (fMRI) becomes increasingly prevalent, with studies examining human brain responses to various attachment figures. However, previous fMRI meta-analyses on affiliative stimuli have encountered challenges, such as low statistical power and the absence of robustness measures. To address these issues, we conducted an exhaustive coordinate-based meta-analysis of 79 fMRI studies, focusing on personalized affiliative stimuli, including one's infants, family, romantic partners, and friends. We employed complementary coordinate-based analyses (Activation Likelihood Estimation and Signed Differential Mapping) and conducted a robustness analysis of the results. Findings revealed cluster convergence in cortical and subcortical structures related to reward and motivation, salience detection, social bonding, and cognition. Our study thoroughly explores the neural correlates underpinning affiliative responses, effectively overcoming the limitations noted in previous meta-analyses. It provides an extensive view of the neural substrates associated with affiliative stimuli, illuminating the intricate interaction between cortical and subcortical regions. Our findings significantly contribute to understanding the neurobiology of human affiliation, expanding the known human attachment circuitry beyond the traditional basal forebrain regions observed in other mammals to include uniquely human isocortical structures.

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.

Knapping force as a function of stone heat treatment

We propose a quantitative framework for understanding the knapping force requirements imposed by different raw materials in their unheated and heat-treated states. Our model interprets stone tool knapping as being the result of cracks formed during the first impact with a hammer stone, followed by continued stressing of these cracks that eventually leads to flake detachment. We combine bending strength, indentation fracture resistance and "Griffith" crack lengths of flint and silcrete to obtain functions identifying critical forces for flaking without or after heat treatment. We argue that these forces are a key factor for understanding the "knappability" of different raw materials, because only forces with 100N or less can be used for very precise strike control. Our model explains for the first time why experimental knappers frequently observe that flint (a stronger material, which, in our case, has a strength above 100 MPa) is easier to knap than silcretes (which is relatively weaker with strength values at or below 60 MPa). Our findings allow for understanding the differences between heat-treated and untreated flint and silcrete in terms of knapping quality, and they allow to compare the qualities of different raw materials.

Molecular archaeology of human cognitive traits

The brains and minds of our human ancestors remain inaccessible for experimental exploration. Therefore, we reconstructed human cognitive evolution by projecting nonsynonymous/synonymous rate ratios (ω values) in mammalian phylogeny onto the anatomically modern human (AMH) brain. This atlas retraces human neurogenetic selection and allows imputation of ancestral evolution in task-related functional networks (FNs). Adaptive evolution (high ω values) is associated with excitatory neurons and synaptic function. It shifted from FNs for motor control in anthropoid ancestry (60-41 mya) to attention in ancient hominoids (26-19 mya) and hominids (19-7.4 mya). Selection in FNs for language emerged with an early hominin ancestor (7.4-1.7 mya) and was later accompanied by adaptive evolution in FNs for strategic thinking during recent (0.8 mya-present) speciation of AMHs. This pattern mirrors increasingly complex cognitive demands and suggests that co-selection for language alongside strategic thinking may have separated AMHs from their archaic Denisovan and Neanderthal relatives.

A novel system for classifying tooth root phenotypes

Human root and canal number and morphology are highly variable, and internal root canal form and count does not necessarily co-vary directly with external morphology. While several typologies and classifications have been developed to address individual components of teeth, there is a need for a comprehensive system, that captures internal and external root features across all teeth. Using CT scans, the external and internal root morphologies of a global sample of humans are analysed (n = 945). From this analysis a method of classification that captures external and internal root morphology in a way that is intuitive, reproducible, and defines the human phenotypic set is developed. Results provide a robust definition of modern human tooth root phenotypic diversity. The method is modular in nature, allowing for incorporation of past and future classification systems. Additionally, it provides a basis for analysing hominin root morphology in evolutionary, ecological, genetic, and developmental contexts.

Territorial blueprint in the hippocampal system

As we skillfully navigate through familiar places, neural computations of distances and coordinates escape our attention. However, we perceive clearly the division of space into socially meaningful territories. 'My space' versus 'your space' is a distinction familiar to all of us. Spatial frontiers are social in nature since they regulate individuals' access to utilities in space depending on hierarchy and affiliation. How does the brain integrate spatial geometry with social territory? We propose that the action of oxytocin (OT) in the entorhinal-hippocampal regions supports this process. Grounded on the functional role of the hypothalamic neuropeptide in the hippocampal system, we show how OT-induced plasticity may bias the geometrical coding of place and grid cells to represent social territories.

The ripples of modernity: How we can extend paleoanthropology with the extended evolutionary synthesis

Contemporary understandings of paleoanthropological data illustrate that the search for a line defining, or a specific point designating, "modern human" is problematic. Here we lend support to the argument for the need to look for patterns in the paleoanthropological record that indicate how multiple evolutionary processes intersected to form the human niche, a concept critical to assessing the development and processes involved in the emergence of a contemporary human phenotype. We suggest that incorporating key elements of the Extended Evolutionary Synthesis (EES) into our endeavors offers a better and more integrative toolkit for modeling and assessing the evolution of the genus Homo. To illustrate our points, we highlight how aspects of the genetic exchanges, morphology, and material culture of the later Pleistocene complicate the concept of "modern" human behavior and suggest that multiple evolutionary patterns, processes, and pathways intersected to form the human niche.

Beyond the Household: Caribbean Families and Biocultural Models of Alloparenting

Alloparental or extramaternal care is an integral aspect of human childrearing. This behavior has been explored both as an extension of the primary mother–infant dyad that evolved to meet the demands of altricial offspring and as an economic exchange of energy and resources. Much of this research centers on foraging or small-scale communities and positions the household as the central unit through which to explore negotiations of care. In this review, I use evidence from Black Caribbean communities living in industrialized countries to challenge the broad applicability of the analytical model of the bounded household and to question whether our current articulations of theory and empirical assessments of extramaternal care are well suited to investigations of these behaviors in the vast majority of contemporary human populations. Alloparental practices in the Caribbean reflect dynamic responses to maternal migration and the local influence of global labor markets. The children who remain at home experience variability in the care received from their surrogate parents. The dynamic aspect of the care practices enacted by these transnational families reveals the behavioral flexibility that has been integral to human survival.

Neanderthals as familiar strangers and the human spark: How the 'golden years' of Neanderthal research reopen the question of human uniqueness

During the past decades, our image of Homo neanderthalensis has changed dramatically. Initially, Neanderthals were seen as primitive brutes. Increasingly, however, Neanderthals are regarded as basically human. New discoveries and technologies have led to an avalanche of data, and as a result of that it becomes increasingly difficult to pinpoint what the difference between modern humans and Neanderthals really is. And yet, the persistent quest for a minimal difference which separates them from us is still noticeable in Neanderthal research. Neanderthal discourse is a vantage point from which the logic of 'us' versus 'other' is critically reconsidered. Studying contemporary academic literature and science autobiographies from an oblique perspective, focusing not on Neanderthals as objects, but on the dynamics of interaction between Neanderthal researchers and their finds, basic convictions at work in this type of research are retrieved. What is at issue is not the actual distinction between modern humans and Neanderthals (which is continuously being redefined), but rather the dualistic construction of human and nonhuman. Neanderthal understanding is affected by the desire to safeguard human uniqueness. The overall trend is to identify the human mark or spark, which defines us as favoured 'winners'. The paradoxes emerging in contemporary Neanderthal discourse are symptomatic of the fact that a dualistic style of thinking is no longer tenable.

Trajectories of cultural innovation from the Middle to Later Stone Age in Eastern Africa: Personal ornaments, bone artifacts, and ocher from Panga ya Saidi, Kenya

African Middle Stone Age (MSA) populations used pigments, manufactured and wore personal ornaments, made abstract engravings, and produced fully shaped bone tools. However, ongoing research across Africa reveals variability in the emergence of cultural innovations in the MSA and their subsequent development through the Later Stone Age (LSA). When present, it appears that cultural innovations manifest regional variability, suggestive of distinct cultural traditions. In eastern Africa, several Late Pleistocene sites have produced evidence for novel activities, but the chronologies of key behavioral innovations remain unclear. The 3 m deep, well-dated, Panga ya Saidi sequence in eastern Kenya, encompassing 19 layers covering a time span of 78 kyr beginning in late Marine Isotope Stage 5, is the only known African site recording the interplay between cultural and ecological diversity in a coastal forested environment. Excavations have yielded worked and incised bones, ostrich eggshell beads (OES), beads made from seashells, worked and engraved ocher pieces, fragments of coral, and a belemnite fossil. Here, we provide, for the first time, a detailed analysis of this material. This includes a taphonomic, archeozoological, technological, and functional study of bone artifacts; a technological and morphometric analysis of personal ornaments; and a technological and geochemical analysis of ocher pieces. The interpretation of the results stemming from the analysis of OES beads is guided by an ethnoarcheological perspective and field observations. We demonstrate that key cultural innovations on the eastern African coast are evident by 67 ka and exhibit remarkable diversity through the LSA and Iron Age. We suggest the cultural trajectories evident at Panga ya Saidi were shaped by both regional traditions and cultural/demic diffusion.

Anterior tooth-use behaviors among early modern humans and Neandertals

Early modern humans (EMH) are often touted as behaviorally advanced to Neandertals, with more sophisticated technologies, expanded resource exploitation, and more complex clothing production. However, recent analyses have indicated that Neandertals were more nuanced in their behavioral adaptations, with the production of the Châtelperronian technocomplex, the processing and cooking of plant foods, and differences in behavioral adaptations according to habitat. This study adds to this debate by addressing the behavioral strategies of EMH (n = 30) within the context of non-dietary anterior tooth-use behaviors to glean possible differences between them and their Neandertal (n = 45) counterparts. High-resolution casts of permanent anterior teeth were used to collect microwear textures of fossil and comparative bioarchaeological samples using a Sensofar white-light confocal profiler with a 100x objective lens. Labial surfaces were scanned, totaling a work envelope of 204 x 276 μm for each individual. The microwear textures were examined for post-mortem damage and uploaded to SSFA software packages for surface characterization. Statistical analyses were performed to examine differences in central tendencies and distributions of anisotropy and textural fill volume variables among the EMH sample itself by habitat, location, and time interval, and between the EMH and Neandertal samples by habitat and location. Descriptive statistics for the EMH sample were compared to seven bioarchaeological samples (n = 156) that utilized different tooth-use behaviors to better elucidate specific activities that may have been performed by EMH. Results show no significant differences between the means within the EMH sample by habitat, location, or time interval. Furthermore, there are no significant differences found here between EMH and Neandertals. Comparisons to the bioarchaeological samples suggest both fossil groups participated in clamping and grasping activities. These results indicate that EMH and Neandertals were similar in their non-dietary anterior tooth-use behaviors and provide additional evidence for overlapping behavioral strategies employed by these two hominins.

Hypotheses for the Evolution of Reduced Reactive Aggression in the Context of Human Self-Domestication

Parallels in anatomy between humans and domesticated mammals suggest that for the last 300,000 years, Homo sapiens has experienced more intense selection against the propensity for reactive aggression than other species of Homo. Selection against reactive aggression, a process that can also be called self-domestication, would help explain various physiological, behavioral, and cognitive features of humans, including the unique system of egalitarian male hierarchy in mobile hunter-gatherers. Here I review nine leading proposals for the occurrence of self-domestication in H. sapiens. To account for the domestication syndrome, proposals must explain what led to a decline in fitness of highly aggressive males, and why the explanatory factor applies only to H. sapiens and not to other species of Homo. The proposed explanations invoke genetic group selection; group-structured culture selection (also known as cultural group selection); social selection by female mate choice; social selection by male partner choice; increased self-control; cooperative breeding; high population density; use of lethal weapons; and language-based conspiracy. Most of these proposals face difficulties in accounting for the origins and/or maintenance of reduced reactive aggression. I conclude that the evolution of language-based conspiracy, which is a form of collective intentionality, was the key factor initiating and maintaining self-domestication in H. sapiens, because it is the most convincing mechanism for explaining the selective pressure against individually powerful fighters. Sophisticated language enabled males of low fighting prowess to cooperatively plan the execution of physically aggressive and domineering alpha males. This system is known today as a leveling mechanism in small-scale societies. Group-structured culture selection possibly accelerated the process.

Self-sacrifice for a cause: The role of ideas and beliefs in motivating human conflict

The role of ideas and beliefs is generally underplayed in Whitehouse's account. However, just as people may feel that their identity is fused with a collective, they may also feel that their identity is fused with an idea (god, history, justice), which can motivate the same type of behaviors that Whitehouse seeks to explain.

A dispersal of Homo sapiens from southern to eastern Africa immediately preceded the out-of-Africa migration

Africa was the birth-place of Homo sapiens and has the earliest evidence for symbolic behaviour and complex technologies. The best-attested early flowering of these distinctive features was in a glacial refuge zone on the southern coast 100–70 ka, with fewer indications in eastern Africa until after 70 ka. Yet it was eastern Africa, not the south, that witnessed the first major demographic expansion, ~70–60 ka, which led to the peopling of the rest of the world. One possible explanation is that important cultural traits were transmitted from south to east at this time. Here we identify a mitochondrial signal of such a dispersal soon after ~70 ka – the only time in the last 200,000 years that humid climate conditions encompassed southern and tropical Africa. This dispersal immediately preceded the out-of-Africa expansions, potentially providing the trigger for these expansions by transmitting significant cultural elements from the southern African refuge.

Seasonal scheduling of shellfish collection in the Middle and Later Stone Ages of southern Africa

This study assesses the seasonal scheduling of shellfish harvesting among hunter-gatherer populations along the southernmost coast of South Africa, based on a large number of serial oxygen isotope analyses of marine mollusk shells from four archaeological sites. The south coast of South Africa boasts an exceptional record of coastal hunter-gatherer occupation spanning the Holocene, the last glacial cycle and beyond. The significance of coastal adaptations, in this region in particular, for later modern human evolution has been prominently debated. Shellfishing behaviors are an important focus for investigation given the dietary and scheduling implications and the abundant archaeological shell remains in numerous sites. Key to better understanding coastal foraging is whether it was limited to one particular season, or year-round. Yet, this has proven very difficult to establish by conventional archaeological methods. This study reconstructs seasonal harvesting patterns by calculating water temperatures from the final growth increment of shells. Results from two Later Stone Age sites, Nelson Bay Cave (together with the nearby Hoffman's Robberg Cave) and Byneskranskop 1, show a pronounced cool season signal, which is unexpected given previous ethnographic documentation of summer as the optimal season for shellfishing activities and inferences about hunter-gatherer scheduling and mobility in the late Holocene. Results from two Middle Stone Age sites, Klasies River and Pinnacle Point 5-6, show distinct seasonal patterns that likely reflect the seasonal availability of resources in the two locations. The Pinnacle Point 5-6 assemblage, which spans the MIS5-4 transition, records a marked shift in shellfishing seasonality at c. 71 ka that aligns with other indications of archaeological and environmental change at this time. We conclude that the scheduling and intensity of shellfishing in this region is affected by a suite of factors, including environmental and cultural drivers, rather than a single variable, such as population growth.

Skeletal Anomalies in The Neandertal Family of El Sidrón (Spain) Support A Role of Inbreeding in Neandertal Extinction

Neandertals disappeared from the fossil record around 40,000 bp, after a demographic history of small and isolated groups with high but variable levels of inbreeding, and episodes of interbreeding with other Paleolithic hominins. It is reasonable to expect that high levels of endogamy could be expressed in the skeleton of at least some Neandertal groups. Genetic studies indicate that the 13 individuals from the site of El Sidrón, Spain, dated around 49,000 bp, constituted a closely related kin group, making these Neandertals an appropriate case study for the observation of skeletal signs of inbreeding. We present the complete study of the 1674 identified skeletal specimens from El Sidrón. Altogether, 17 congenital anomalies were observed (narrowing of the internal nasal fossa, retained deciduous canine, clefts of the first cervical vertebra, unilateral hypoplasia of the second cervical vertebra, clefting of the twelfth thoracic vertebra, diminutive thoracic or lumbar rib, os centrale carpi and bipartite scaphoid, tripartite patella, left foot anomaly and cuboid-navicular coalition), with at least four individuals presenting congenital conditions (clefts of the first cervical vertebra). At 49,000 years ago, the Neandertals from El Sidrón, with genetic and skeletal evidence of inbreeding, could be representative of the beginning of the demographic collapse of this hominin phenotype.

Considering selection pressures for identity fusion and self-sacrifice in small-scale societies

Whitehouse's view that our ultrasocial species evolved in small, warring bands is questioned, and alternative social selection pressures for the evolution of identity fusion and self-sacrifice in small-scale societies are proposed. Short durations of states of fusion allow for re-evaluation of risks; the consolidation of episodic memories into collective oral traditions elicits cooperation. Dysmorphic memories may be more powerful in generating identity fusion when followed by euphoric ones, as in “rites of torture” in male initiations.

Clarifying distinct models of modern human origins in Africa

Accumulating genomic, fossil and archaeological data from Africa have led to a renewed interest in models of modern human origins. However, such discussions are often discipline-specific, with limited integration of evidence across the different fields. Further, geneticists typically require explicit specification of parameters to test competing demographic models, but these have been poorly outlined for some scenarios. Here, we describe four possible models for the origins of Homo sapiens in Africa based on published literature from paleoanthropology and human genetics. We briefly outline expectations for data patterns under each model, with a special focus on genetic data. Additionally, we present schematics for each model, doing our best to qualitatively describe demographic histories for which genetic parameters can be specifically attached. Finally, it is our hope that this perspective provides context for discussions of human origins in other manuscripts presented in this special issue.

Evidence for close-range hunting by last interglacial Neanderthals

Animal resources have been part of hominin diets since around 2.5 million years ago, with sharp-edged stone tools facilitating access to carcasses. How exactly hominins acquired animal prey and how hunting strategies varied through time and space is far from clear. The oldest possible hunting weapons known from the archaeological record are 300,000 to 400,000-year-old sharpened wooden staves. These may have been used as throwing and/or close-range thrusting spears, but actual data on how such objects were used are lacking, as unambiguous lesions caused by such weapon-like objects are unknown for most of human prehistory. Here, we report perforations observed on two fallow deer skeletons from Neumark-Nord, Germany, retrieved during excavations of 120,000-year-old lake shore deposits with abundant traces of Neanderthal presence. Detailed studies of the perforations, including micro-computed tomography imaging and ballistic experiments, demonstrate that they resulted from the close-range use of thrusting spears. Such confrontational ways of hunting require close cooperation between participants, and over time may have shaped important aspects of hominin biology and behaviour.

Phytoliths as an indicator of early modern humans plant gathering strategies, fire fuel and site occupation intensity during the Middle Stone Age at Pinnacle Point 5-6 (south coast, South Africa)

The study of plant remains in archaeological sites, along with a better understanding of the use of plants by prehistoric populations, can help us shed light on changes in survival strategies of hunter-gatherers and consequent impacts on modern human cognition, social organization, and technology. The archaeological locality of Pinnacle Point (Mossel Bay, South Africa) includes a series of coastal caves, rock-shelters, and open-air sites with human occupations spanning the Acheulian through Middle Stone Age (MSA) and Later Stone Age (LSA). These sites have provided some of the earliest evidence for complex human behaviour and technology during the MSA. We used phytoliths-amorphous silica particles that are deposited in cells of plants-as a proxy for the reconstruction of past human plant foraging strategies on the south coast of South Africa during the Middle and Late Pleistocene, emphasizing the use and control of fire as well as other possible plant uses. We analysed sediment samples from the different occupation periods at the rock shelter Pinnacle Point 5-6 North (PP5-6N). We also present an overview of the taphonomic processes affecting phytolith preservation in this site that will be critical to conduct a more reliable interpretation of the original plant use in the rock shelter. Our study reports the first evidence of the intentional gathering and introduction into living areas of plants from the Restionaceae family by MSA hunter-gatherers inhabiting the south coast of South Africa. We suggest that humans inhabiting Pinnacle Point during short-term occupation events during Marine Isotope Stage (MIS) 5 built fast fires using mainly grasses with some wood from trees and/or shrubs for specific purposes, perhaps for shellfish cooking. With the onset of MIS 4 we observed a change in the plant gathering strategies towards the intentional and intensive exploitation of dry wood to improve, we hypothesise, combustion for heating silcrete. This human behaviour is associated with changes in stone tool technology, site occupation intensity and climate change.

Middle and Later Stone Age chronology of Kisese II rockshelter (UNESCO World Heritage Kondoa Rock-Art Sites), Tanzania

The archaeology of East Africa during the last ~65,000 years plays a central role in debates about the origins and dispersal of modern humans, Homo sapiens. Despite the historical importance of the region to these discussions, reliable chronologies for the nature, tempo, and timing of human behavioral changes seen among Middle Stone Age (MSA) and Later Stone Age (LSA) archaeological assemblages are sparse. The Kisese II rockshelter in the Kondoa region of Tanzania, originally excavated in 1956, preserves a ≥ 6-m-thick archaeological succession that spans the MSA/LSA transition, with lithic artifacts such as Levallois and bladelet cores and backed microliths, the recurrent use of red ochre, and >5,000 ostrich eggshell beads and bead fragments. Twenty-nine radiocarbon dates on ostrich eggshell carbonate make Kisese II one of the most robust chronological sequences for understanding archaeological change over the last ~47,000 years in East Africa. In particular, ostrich eggshell beads and backed microliths appear by 46-42 ka cal BP and occur throughout overlying Late Pleistocene and Holocene strata. Changes in lithic technology suggest an MSA/LSA transition that began 39-34.3 ka, with typical LSA technologies in place by the Last Glacial Maximum. The timing of these changes demonstrates the time-transgressive nature of behavioral innovations often linked to the origins of modern humans, even within a single region of Africa.

Lithic technological responses to Late Pleistocene glacial cycling at Pinnacle Point Site 5-6, South Africa

There are multiple hypotheses for human responses to glacial cycling in the Late Pleistocene, including changes in population size, interconnectedness, and mobility. Lithic technological analysis informs us of human responses to environmental change because lithic assemblage characteristics are a reflection of raw material transport, reduction, and discard behaviors that depend on hunter-gatherer social and economic decisions. Pinnacle Point Site 5-6 (PP5-6), Western Cape, South Africa is an ideal locality for examining the influence of glacial cycling on early modern human behaviors because it preserves a long sequence spanning marine isotope stages (MIS) 5, 4, and 3 and is associated with robust records of paleoenvironmental change. The analysis presented here addresses the question, what, if any, lithic assemblage traits at PP5-6 represent changing behavioral responses to the MIS 5-4-3 interglacial-glacial cycle? It statistically evaluates changes in 93 traits with no a priori assumptions about which traits may significantly associate with MIS. In contrast to other studies that claim that there is little relationship between broad-scale patterns of climate change and lithic technology, we identified the following characteristics that are associated with MIS 4: increased use of quartz, increased evidence for outcrop sources of quartzite and silcrete, increased evidence for earlier stages of reduction in silcrete, evidence for increased flaking efficiency in all raw material types, and changes in tool types and function for silcrete. Based on these results, we suggest that foragers responded to MIS 4 glacial environmental conditions at PP5-6 with increased population or group sizes, 'place provisioning', longer and/or more intense site occupations, and decreased residential mobility. Several other traits, including silcrete frequency, do not exhibit an association with MIS. Backed pieces, once they appear in the PP5-6 record during MIS 4, persist through MIS 3. Changing paleoenvironments explain some, but not all temporal technological variability at PP5-6.

Neandertals revised

The last decade has seen a significant growth of our knowledge of the Neandertals, a population of Pleistocene hunter-gatherers who lived in (western) Eurasia between ∼400,000 and 40,000 y ago. Starting from a source population deep in the Middle Pleistocene, the hundreds of thousands of years of relative separation between African and Eurasian groups led to the emergence of different phenotypes in Late Pleistocene Europe and Africa. Both recently obtained genetic evidence and archeological data show that the biological and cultural gaps between these populations were probably smaller than previously thought. These data, reviewed here, falsify inferences to the effect that, compared with their near-modern contemporaries in Africa, Neandertals were outliers in terms of behavioral complexity. It is only around 40,000 y ago, tens of thousands of years after anatomically modern humans first left Africa and thousands of years after documented interbreeding between modern humans, Neandertals and Denisovans, that we see major changes in the archeological record, from western Eurasia to Southeast Asia, e.g., the emergence of representational imagery and the colonization of arctic areas and of greater Australia (Sahul).

The evolution of inequality

Understanding how systems of political and economic inequality evolved from relatively egalitarian origins has long been a focus of anthropological inquiry. Many hypotheses have been suggested to link socio-ecological features with the rise and spread of inequality, and empirical tests of these hypotheses in prehistoric and extant societies are increasing. In this review, we synthesize several streams of theory relevant to understanding the evolutionary origins, spread, and adaptive significance of inequality. We argue that while inequality may be produced by a variety of localized processes, its evolution is fundamentally dependent on the economic defensibility and transmissibility of wealth. Furthermore, these properties of wealth could become persistent drivers of inequality only following a shift to a more stable climate in the Holocene. We conclude by noting several key areas for future empirical research, emphasizing the need for more analyses of contemporary shifts toward institutionalized inequality as well as prehistoric cases.

The shaping of human diversity: filters, boundaries and transitions

The evolution of modern humans was a complex process, involving major changes in levels of diversity through time. The fossils and stone tools that record the spatial distribution of our species in the past form the backbone of our evolutionary history, and one that allows us to explore the different processes-cultural and biological-that acted to shape the evolution of different populations in the face of major climate change. Those processes created a complex palimpsest of similarities and differences, with outcomes that were at times accelerated by sharp demographic and geographical fluctuations. The result is that the population ancestral to all modern humans did not look or behave like people alive today. This has generated questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of Homo sapiens The paucity of African fossils remains a serious stumbling block for exploring some of these issues. However, fossil and archaeological discoveries increasingly clarify important aspects of our past, while breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of Late Quaternary Eurasian hominin groups and their interactions, as well as those between foragers and farmers. This paper explores the nature and timing of key moments in the evolution of human diversity, moments in which population collapse followed by differential expansion of groups set the conditions for transitional periods. Five transitions are identified (i) at the origins of the species, 240-200 ka; (ii) at the time of the first major expansions, 130-100 ka; (iii) during a period of dispersals, 70-50 ka; (iv) across a phase of local/regional structuring of diversity, 45-25 ka; and (v) during a phase of significant extinction of hunter-gatherer diversity and expansion of particular groups, such as farmers and later societies (the Holocene Filter), 15-0 ka.This article is part of the themed issue 'Major transitions in human evolution'.

The transition to foraging for dense and predictable resources and its impact on the evolution of modern humans

Scientists have identified a series of milestones in the evolution of the human food quest that are anticipated to have had far-reaching impacts on biological, behavioural and cultural evolution: the inclusion of substantial portions of meat, the broad spectrum revolution and the transition to food production. The foraging shift to dense and predictable resources is another key milestone that had consequential impacts on the later part of human evolution. The theory of economic defendability predicts that this shift had an important consequence-elevated levels of intergroup territoriality and conflict. In this paper, this theory is integrated with a well-established general theory of hunter-gatherer adaptations and is used to make predictions for the sequence of appearance of several evolved traits of modern humans. The distribution of dense and predictable resources in Africa is reviewed and found to occur only in aquatic contexts (coasts, rivers and lakes). The palaeoanthropological empirical record contains recurrent evidence for a shift to the exploitation of dense and predictable resources by 110 000 years ago, and the first known occurrence is in a marine coastal context in South Africa. Some theory predicts that this elevated conflict would have provided the conditions for selection for the hyperprosocial behaviours unique to modern humans.This article is part of the themed issue 'Major transitions in human evolution'.