Cooperation is widely viewed as a stabilizing force because it pools risk and buffers against environmental uncertainty. Demographic theory predicts that volatility in per-capita population growth declines rapidly with population size, implying that larger populations should be more stable. Yet human societies of all sizes eventually collapse. Here, we propose a general mechanism that helps explain this pattern. We show that cooperation generates demographic synchrony-correlated survival and reproductive outcomes among individuals-which inflates aggregate volatility. Using more than 200 longitudinal population records from indigenous societies in the Brazilian Amazon, we find that volatility declines with population size substantially slower than predicted under demographic independence. This pattern implies pervasive within-population correlation, such that census populations behave demographically as if composed of far fewer independent modules. We formalize this process with a synchrony-extended stochastic model in which shared environmental exposure, social coupling, and spatial overlap generate demographic correlations that erode the stabilizing effects of scale. We term this dynamic the cooperation-synchrony paradox: the same institutions that reduce risk for individuals can increase vulnerability to population-wide shocks. Further, we propose this is likely a general mechanism across species, where cooperation stabilizes locally but generates systemic fragility by reducing effective demographic dimensionality.

This study examines the fluting of two well-known Late Pleistocene fluted point types in North America: Clovis and Folsom. Using scaling analyses, we assess the changing relationship between flute length and point length in a large sample of each type. Researchers use scaling to investigate the physical constraints of an object and determine how its dimensions change with size. We compare the strength and consistency of the scaling relationships between the older Clovis and the younger Folsom with the aim of shedding light on scaling differences, if any, over their temporal span. Our results show that there is a significant difference in the relationship of fluting length to point length between these types. In Folsom point manufacture, flute length increases nearly twice as fast with increasing point length than in Clovis. Importantly, the scaling of flute length to point length relationship is isometric (linear) in the Folsom sample, whereas it is allometric (sublinear) in the Clovis sample. In other words, Folsom flintknappers maintained a constant ratio of flute length to point length. Clovis flintknappers were less concerned about maintaining this ratio. We attribute this difference to a potentially increasing, or changing, functional role of fluting in Folsom.

This work presents an interactive Virtual Reality (VR) application to enhance education on Amazonian geoglyphs. Many Amazonian archaeological sites are difficult to reach and visualize as they are hidden by dense rainforest foliage. Using a combination of VR technology and LiDAR (Light Detection and Ranging) data, we generate scale models of geoglyphs without the current foliage. We use this model to create a reconstruction of the historical usage of these earthworks, based on current archaeological and anthropological interpretations. The experience is enhanced by using reconstructions of artifacts commonly found in the vicinity of these geoglyphs.

Amazonia is an invaluable global asset for all its ecological and cultural significance. Indigenous peoples and their lands are pivotal in safeguarding this unique biodiversity and mitigating global climate change. Understanding the causal structure behind variation in the degree of environmental conservation across different indigenous lands-each with varying institutional, legal, and socioenvironmental conditions-is an essential source of information in the struggle for long-term sustainable management of Amazonian ecosystems. Here, we use data from the Instituto Socioambiental for 361 indigenous lands in the Brazilian Amazon coded for environmental integrity, territorial integrity, legal stability, indigenous governance, and threats due to infrastructure projects. Using Bayesian networks to learn the causal structure amongst these variables reveals two causal pathways leading to environmental integrity. One causal pathway starts with territorial integrity and is mediated by infrastructure projects, while the other is directly from legal stability. Hence, safeguarding indigenous lands from exploitation is best accomplished via legal land rights and stricter enforcement instead of placing the onus on indigenous governance, which is also a direct outcome of legal stability.

Topographic relief potentially played an important role in Stone Age hunting from the Middle Paleolithic onwards. Natural physical features like arroyos and cliffs, among many others, likely served as traps to stop or hinder animal movement. Yet, the presence of elevation and slope variation on a landscape means that hunters also may have been able to use terrain to hunt from on high. Here, we explored via archaeological experiment how an elevated position would have interacted with projectile weaponry via the force of gravity to influence a missile's functional efficacy. We assessed the velocity and kinetic impact energy of two Paleolithic projectile weapon systems, the thrown javelin and the atlatl (spearthrower) and dart, at ground level and then at three-, six-, and nine-meter launch heights. The experimental results of the javelin supported our predictions. Velocity and kinetic impact energy increased as launch height increased. Unexpectedly, however, atlatl-propelled darts did not conform to our predictions, not only failing to increase dart velocity or kinetic impact energy as launch height increased but also decreasing both variables' values. These results suggest that Paleolithic hunting with an atlatl in certain contexts likely came with consequential, and previously undocumented, opportunity costs. Our results also have implications for several aspects of archaeological interpretation in Paleolithic and postPaleolithic contexts.

Human lifestyles vary enormously over time and space and so understanding the origins of this diversity has always been a central focus of anthropology. A major source of this cultural variation is the variation in institutional complexity: the cultural packages of rules, norms, ontologies and expectations passed down through societies across generations. In this article, we study the emergence of institutions in small-scale societies. There are two primary schools of thought. The first is that institutions emerge top-down as rules are imposed by elites on their societies in order to gain asymmetrical access to power, resources and influence over others through coercion. The second is that institutions emerge bottom-up to facilitate interactions within populations as they seek collective solutions to adaptive problems. Here, we use Bayesian networks to infer the causal structure of institutional complexity in 172 small-scale societies across ethnohistoric western North America reflecting the wide diversity of indigenous lifestyles across this vast region immediately prior to European colonization. Our results suggest that institutional complexity emerges from underlying socioecological complexity because institutions are solutions to coordination problems in more complex environments where human-environment interactions require increased management.

This study is an assessment of Clovis spear thrusting penetration depth and entry wound size. This work is the fifth contribution in a series of experiments aimed at shedding light on the functional performance of distinct Clovis point forms. Here, using highly controlled and standardized procedures, we had a participant who had previously trained with bayonets and hand-to-hand combat thrust seven spears, each tipped with a distinct Clovis point form, into a ballistic gel target. Our statistical analysis of the 203 thrusts revealed, among several findings, that Clovis plan-view form does influence penetration depth and entry wound size. This result is consistent with the hypothesis that the functional selection of attributes could have contributed to Clovis point form variation.

Researchers use a variety of target materials, and sometimes combinations of materials, in their archaeological experiments to examine thrust-spear or projectile penetration, impact angle, durability, and other issues involving prehistoric hunting weaponry. This variety of target materials is beneficial to archaeological science in several ways, but it may also hinder the comparison of results because many of these target materials do not necessarily share similar physical properties. Here, we assess the penetration properties of four different target materials-store-bought meat, clay, and two types of gelatin-via static penetration tests of a modern broadhead-tipped arrow and a stone-tipped projectile attached to an Instron Universal Materials Tester. Our analyses of load-deflection curves, peak load, and work energy demonstrate how the four target materials are similar in some ways but different in others, which suggests that researchers may strategically employ one or several depending on the question asked or hypothesis tested.

Although deforestation remains a continuing threat to both the natural world and its resident human populations, a countervailing land cover dynamic has been observed in many nations. This process of landscape turnaround, the so-called forest transition, holds the potential of regenerating ecosystem services by sparing land from agricultural activities and abandoning it to forest succession. Here, we present a case study of a long-term process of forest transition that is ongoing in the Patzcuaro watershed of the state of Michoacán, Mexico. The research to be discussed comprises a remote sensing analysis designed to (1) capture the land cover impacts of a multidecadal process of trade liberalization (1996–2018); (2) ascertain the role that land tenure plays in land use dynamics affecting forest cover, and (3) resolve forest cover types into native forest, secondary vegetation, and “commodity” covers of fruit trees, in this case, avocado. Mexico presents a useful case for addressing these three design elements. Our analysis, undertaken for both private property and collective modes of resource management in five communities, reveals a forest transition annualized at 20 ha-yr−1, or a gain of eight percent for the period. This translates into a relative rate of forest transition of 0.39%-yr−1 which is three times faster than what is occurring in the temperate biome on a national scale (0.07%-yr−1). Most of the forest transition is occurring on private holdings and stems from field abandonment as farming systems intensify production with avocado plantations and cow–calf operations. As this study demonstrates, forest transitions are not occurring ubiquitously across nations but instead are highly localized occurrences driven by a myriad of distal and proximate factors involving disparate sets of stakeholders. Consequently, policy makers who are keen to expand forest transitions to fulfill their national climate action commitments under the Paris Agreement must first promote research into the complexity of landscapes and drivers of land change at regional and local scales.

The evolution of the hominin hand has been widely linked to the use and production of flaked stone tool technologies. After the earliest handheld flake tools emerged, shifts in hominin hand anatomy allowing for greater force during precision gripping and ease when manipulating objects in-hand are observed in the fossil record. Previous research has demonstrated how biometric traits, such as hand and digit lengths and precision grip strength, impact functional performance and ergonomic relationships when using flake and core technologies. These studies are consistent with the idea that evolutionary selective pressures would have favoured individuals better able to efficiently and effectively produce and use flaked stone tools. After the advent of composite technologies during the Middle Stone Age and Middle Palaeolithic, fossil evidence reveals differences in hand anatomy between populations, but there is minimal evidence for an increase in precision gripping capabilities. Furthermore, there is little research investigating the selective pressures, if any, impacting manual anatomy after the introduction of hafted composite stone technologies ('handles'). Here we investigated the possible influence of tool-user biometric variation on the functional performance of 420 hafted Clovis knife replicas. Our results suggest there to be no statistical relationships between biometric variables and cutting performance. Therefore, we argue that the advent of hafted stone technologies may have acted as a 'performance equaliser' within populations and removed (or reduced) selective pressures favouring forceful precision gripping capabilities, which in turn could have increased the relative importance of cultural evolutionary selective pressures in the determination of a stone tool's performance.

Bullet ricochets are common occurrences during shooting incidents and can provide a wealth of information useful for shooting incident reconstruction. However, there have only been a small number of studies that have systematically investigated bullet ricochet impact site morphology. Here, this study reports on an experiment that examined the plan-view morphology of 297 ricochet impact sites in concrete that were produced by five different bullet types shot from two distances. This study used a random forest machine learning algorithm to classify bullet types with morphological dimensions of the ricochet mark (impact) with length and perimeter-to-area ratio emerging as the top predictor variables. The 0.22 LR leaves the most distinctive impact mark on the concrete, and overall, the classification accuracy using leave-one-out cross-validation is 62%, considerably higher than a random classification accuracy of 20%. Adding in distance to the model as a predictor increases the classification accuracy to 66%. These initial results are promising, in that they suggest that an unknown bullet type can potentially be determined, or at least probabilistically assessed, from the morphology of the ricochet impact site alone. However, the substantial amount of overlap this study documented among distinct bullet types' ricochet mark morphologies under highly controlled conditions and with machine learning suggests that the human identification of ricochet marks in real-world shooting incident reconstructions may be on occasion, or perhaps regularly, in error. Key points:Bullet ricochet impact sites can help with shooting incident reconstruction.A random forest machine learning algorithm classified bullet type from ricochet morphology.Results suggest that unknown bullets can potentially be determined from ricochet impact site morphology.Human identification of bullet types from ricochet sites may be erroneous.

In searching for a child's musical imagination, some questions spring to mind as being important preliminaries. Gardner regards what he calls musical intelligence as one of man's finite number of intelligences, along with spatial, logical-mathematical, and others. Interestingly, he explains the term by reference to the behaviour of unassailably musical adults. In claiming that no other intelligence 'emerges earlier than musical talent', he cites examples of precocious behaviour in children as the manifestation of musical intelligence, at least in western culture or, more precisely, recent western culture. Some African tribal music contains enormously complex or tediously repetitive (to the western ear) rhythms played on sticks and drums and voices chanting pitches that western music does not utilize. Today, in contrast, no one would have any compunction at agreeing that all three composers displayed what can be called musical imagination, and not just in comparison with any mediocrity that surrounded them.

Isolated indigenous societies who actively avoid sustained peaceful contact with the outside world are critically endangered. Last year, “Tanaru”, the lone surviving man of his tribe for at least 35 years, died in Southwest Amazonia, marking the latest cultural extinction event in a long history of massacres, enslavement, and epidemics. Yet in the upper reaches of the Amazon Basin, dozens of resilient isolated tribes still manage to survive. Remote sensing is a reliable method of monitoring the population dynamics of uncontacted populations by quantifying the area cleared for gardens and villages, along with the fire detections associated with the burning of those clearings. Remote sensing also provides a method to document the number of residential structures and village fissioning. Only with these longitudinal assessments can we better evaluate the current no-contact policies by the United Nations and governments, along with the prospects for the long-term survival of isolated tribes. While the world’s largest isolated indigenous metapopulation, Pano speakers in Acre, Brazil, appears to be thriving, other smaller isolated populations disconnected from metapopulations continue to be extremely vulnerable to external threats. Our applied anthropological conservation approach is to provide analyses of publicly available remote sensing datasets to help inform policies that enhance the survival and well-being of isolated cultural groups.

"Tapajós" narrates the field campaign of two researchers studying forest fragmentation in the Brazilian Amazon. It addresses a contemporary conflict in the region, where an Indigenous people, the Munduruku, are resisting efforts by the Brazilian State to channelize the Tapajós River and exploit its hydropower potential. Development here represents an existential threat to the Munduruku, whose homeland resides in the river valley. It also represents an ecological threat to the global community. Although the rate of deforestation dropped after the turn of the millennium, it has begun to climb again and would no doubt accelerate with development in the Tapajós watershed and the opening of Central Amazonia to colonization and resource extraction. This would push the forest past its tipping point, a magnitude of deforestation capable of compromising rainfall recycling, and thus precipitating the transformation of the Amazonian forest into a patchwork of fireadapted shrubs and grasses. "Tapajós" describes how such an ecological catastrophe would occur. It also argues that the assertion of Indigenous territorial rights is key to the conservation of Amazonian biodiversity. The account unfolds against a background of conflict between Amazonia's Indigenous peoples and the Brazilian State. In so doing, it brings to life the realities of frontier violence involving both land conflict and the unrestrained behaviors of individuals living outside the institutional constraints of law. Such violence complicates the execution of field research in the region and contributes to its gathering ecological crisis.

Amazonia has as least two major centers of ancient human social complexity, but the full geographic extents of these centers remain uncertain. Across the southern rim of Amazonia, over 1,000 earthwork sites comprised of fortified settlements, mound villages, and ditched enclosures with geometric designs known as geoglyphs have been discovered. Qualitatively distinct and densely located along the lower stretches of major river systems and the Atlantic coast are Amazonian Dark Earth sites (ADEs) with deep anthropogenic soils enriched by long-term human habitation. Models predicting the geographic extents of earthworks and ADEs can assist in their discovery and preservation and help answer questions about the full degree of indigenous landscape modifications across Amazonia. We classify earthworks versus ADEs versus other non-earthwork/non-ADE archaeological sites with multi-class machine learning algorithms using soils, climate, and distances to rivers of different types and sizes as geospatial predictors. Model testing is done with spatial cross-validation, and the best model at the optimal spatial scale of 1 km has an Area Under the Curve of 0.91. Our predictive model has led to the discovery of 13 new geoglyphs, and it pinpoints specific areas with high probabilities of undiscovered archaeological sites that are currently hidden by rainforests. The limited, albeit impressive, predicted extents of earthworks and ADEs means that other non-ADE/non-earthwork sites are expected to predominate most of Western and Northern Amazonia.

Stone Age hunter-gatherers likely often had choices concerning the raw materials used in the production of their technologies. How different raw materials performed once transformed into tools was one potential consideration that influenced raw material choices. Here, we present an experiment comparing replica Late Pleistocene North American Clovis culture osseous weapon tips versus stone tips in terms of how well each penetrates a target. We focused our efforts specifically on bone and stone point forms similar to those from the Sheriden Cave site, Ohio. Our results show that the bone point form penetrated significantly shallower than the stone point form. This result is consistent with the hypothesis that penetration depth was not a motivating factor in the production of bone point forms at Sheriden Cave. We suggest that other factors, such as raw material availability, craftsperson skill and experience, or tool durability may better explain the presence of bone points at the site. However, more broadly, our study illustrates that experiments do not provide answers about the past, but instead should be employed as theoretical tools to help frame testing and interpretation of the archaeological record.

The atlatl is a handheld, rod-shaped device that employs leverage to launch a dart, and represents a major human technological innovation. One hypothesis for forager atlatl adoption over its presumed predecessor, the thrown javelin, is that a diverse array of people could achieve equal performance results, thereby facilitating inclusive participation of more people in hunting activities. We tested this hypothesis via a systematic assessment of 2160 weapon launch events by 108 people who used both technologies. Our results show that, unlike the javelin, the atlatl equalizes the velocity of female- and male-launched projectiles. This result indicates that a javelin to atlatl transition would have promoted a unification, rather than division, of labor. Moreover, our results suggest that female and male interments with atlatl weaponry should be interpreted similarly.