How and why early hunter-gatherers expanded into the challenging environments of the Tibetan Plat... more How and why early hunter-gatherers expanded into the challenging environments of the Tibetan Plateau during the Pleistocene remain largely unexplained. The discovery of the archaeological site of Nwya Devu, characterized by lithic blade production, brings new evidence of human expansion to high elevations ca. 40-30 ka. The blade assemblage currently lacks technological antecedents in East Asia. During Marine Isotope Stage 3, the surrounding lowlands to the Plateau were dominated by a distinct type of industry broadly named "core and flake." It is suggested that the Nwya Devu blade assemblage derives from traditions in the eastern Eurasian Steppe, a clustered hub for Upper Paleolithic blade technology. In contrast to the East Asian lowlands, the Tibetan Plateau shares a number of environmental similarities with North and Central Asia such as low temperature and humidity, long winters, strong seasonality, and grassland landscapes. Blade and core-and-flake technologies tend to be associated with different environments in eastern Asia. We hypothesize that this geographic distribution indicates different sets of behavioral adaptations that map onto distinct ecozones and are relevant to human expansion to the Tibetan Plateau during Marine Isotope Stage 3. To evaluate the working model, we characterized the environmental parameters for both blade and core-and-flake technologies in eastern Asia during the period. The results show that environmental conditions on the Plateau and at the Nwya Devu site align with those of blade assemblages documented in the Eurasian Steppe and contrast with those of core-and-flake assemblages. Blade technology is strongly associated with low-temperature environments. These findings suggest that hunter-gatherers from the steppe belt may have benefited from their behaviorally adaptive advantages when moving into the highland environments of the Tibetan Plateau, 40-30 ka.
Human societies are characterized by norms that restrict selfish behavior and promote cooperation... more Human societies are characterized by norms that restrict selfish behavior and promote cooperation. The oxytocin system is an important modulator of social behavior that may be involved in the evolution of cooperation. Oxytocin acts in both the nucleus accumbens and the anterior cingulate cortex to promote social bonding and social cohesion. Expression of the CD38 and OXTR genes is known to affect oxytocin secretion and binding, respectively, in these brain areas. The Andean highlands provide an excellent opportunity to evaluate the role of oxytocin in the evolution of cooperation. The rich archeological record spans 13,000 years of population growth and cooperative challenges through periods of highland exploration, hunting economies, agro-pastoralism, and urbanization. Through allele trajectory modeling using both ancient and contemporary whole genomes, we find evidence for strong positive selection on the OXTR and CD38 alleles linked with increased oxytocin signaling. These selection events commenced around 2.5 and 1.25 thousand years ago, placing them in the region's Upper Formative and Tiwanaku periods-a time of population growth, urbanization, and relatively low rates of violence. Along with remarkable and enduring cultural developments, increased oxytocin secretion and receptor binding in these brain areas may have facilitated large-scale cooperation that promoted early urbanization in the Titicaca Basin of the Andean highlands.
Satellite survey is widely used for archaeological site discovery, but the efficacy of the method... more Satellite survey is widely used for archaeological site discovery, but the efficacy of the method has received little systematic investigation. In this analysis, twelve study participants of different experience levels performed an unstructured remote survey of 197 km 2 in the Sama and Moquegua valleys of south central Peru where previous pedestrian surveys recorded 546 archaeological sites. Results indicate an average site discovery rate of 9.3% (0-18%, 95% range). The most experienced participants detect up to 20% (17-22%) of known archaeological sites. These detection rates can be used to derive reliable site frequency estimates on the Andean coast, which can be used in planning and budgeting for field efforts and estimating demographic patterns at large spatial scales that are difficult to achieve through pedestrian survey. More generally, this analysis offers a method for deriving correction terms specific to other parts of the world. Additionally, the results can serve as a baseline for evaluating the effectiveness of emerging artificial intelligence routines for archaeological site detection.
Neolithization was a complex, protracted process of domestication, sedentarization, and technolog... more Neolithization was a complex, protracted process of domestication, sedentarization, and technology change that occurred in various combinations in various times and places around the world. Understanding the causal relationships among those and other important human behaviors remains an analytical challenge. This study examines Neolithization through the lens of lithic artifact variation in the Lake Titicaca Basin, Peru. Drawing on previous lithics research, we outline a synthetic model linking changing diet, mobility, and projectile technology to predicted trends in lithic assemblages. The expectations are then compared to two large, well-dated lithic assemblages from the Titicaca Basin—one from the Middle/Late Archaic forager site of Soro Mik’aya Patjxa (8.0–6.5 cal. ka) and the other from the Terminal Archaic horticultural site of Jiskairumoko (5.2–3.4 cal. ka). We find that the strongest signal in lithic technology change is related to the introduction of archery technology. Sig...
Current models of early human subsistence economies suggest a focus on large mammal hunting. To e... more Current models of early human subsistence economies suggest a focus on large mammal hunting. To evaluate this hypothesis, we examine human bone stable isotope chemistry of 24 individuals from the early Holocene sites of Wilamaya Patjxa (9.0–8.7 cal. ka) and Soro Mik’aya Patjxa (8.0–6.5 cal. ka) located at 3800 meters above sea level on the Andean Altiplano, Peru. Contrary to expectation, Bayesian mixing models based on the isotope chemistry reveal that plants dominated the diet, comprising 70–95% of the average diet. Paleoethnobotanical data further show that tubers may have been the most prominent subsistence resource. These findings update our understanding of earliest forager economies and the pathway to agricultural economies in the Andean highlands. The findings furthermore suggest that the initial subsistence economies of early human populations adapting to new landscapes may have been more plant oriented than current models suggest.
Oxford Research Encyclopedia of Anthropology, 2023
The Andean highlands of western South America spans 7,000 km from the equator to Patagonia and re... more The Andean highlands of western South America spans 7,000 km from the equator to Patagonia and reaches altitudes of 7,000 m. Extreme cold, hypoxia, and low bioproductivity impose a distinct set of challenges to human survival and reproduction. This adaptive setting has inspired considerable archaeological and genetic research, which seeks to define the timing and nature of the adaptive process. Current evidence establishes that Paleoindian populations with fluted-point projectile technology first entered the highlands around 12.8 cal. ka. Paleoindian use of the highlands over the subsequent one thousand years appears to have been ephemeral. During the Early Archaic period (11.7–9.0 cal. ka), a culturally and genetically distinct population appears to have replaced the Paleoindian population in the highlands where they eventually established year-round settlement systems. Early Archaic cultural adaptations included large-mammal hunting, tuber foraging, animal-hide technology, logistical mobility, and egalitarian social structure. Potential genetic adaptations include selection for respiratory and cardiovascular strength and enhanced starch digestion capacity. Human adaptation to the Andean highlands thus appears to have been a multifaceted process that transpired over some four thousand years. Although current evidence favors a model of gradual adaptation, a more rapid adaptive process cannot yet be excluded. Paleoindian sites remain woefully sparse, which may indicate limited use or a sampling problem. And although recent genetic and isotopic analyses have been incisive, they are restricted to few samples from relatively late contexts. Continued investigations at the intersection of traditional archaeological methods and new biomolecular methods are likely to resolve outstanding questions soon and create opportunities to explore more-nuanced questions about the peopling of the high Andes.
The extent to which archery technology affected social organization in the Andes region of South ... more The extent to which archery technology affected social organization in the Andes region of South America remains understudied. To identify the timing and consequences of archery technology in the Lake Titicaca Basin, this analysis examines metric data from 1179 projectile points from the region, 11-1.0 cal. ka. We find that the greatest decrease in projectile point size occurred across the Late/Terminal Archaic and Formative/Tiwanaku period boundaries, 5.0 and 1.5 cal. ka, respectively. We do not find a statistically significant decrease in size during any other transition, including the Terminal Archaic/Formative boundary, which was previously hypothesized to have been the time when archery technology first appeared in the region. These results instead favor the hypothesis that archery technology first entered the region during the Terminal Archaic Period, 5.0-3.5 cal ka. We furthermore observe that this technological transition coincided with the growth of settlements, a surge in the use of exotic goods such as obsidian, a low level of inter-group violence, and incipient agropastoralism-a pattern that intensified during the subsequent Formative period when monumental ceremonial centers emerged. These findings lead us to propose a model for South American archery technology in which its appearance after 5000 years ago contributed to the emergence of new cooperative dynamics that expanded regional exchange networks and community aggregation.
Approximately 9000 years ago at the Andean highland site of Wilamaya Patjxa, forager communities ... more Approximately 9000 years ago at the Andean highland site of Wilamaya Patjxa, forager communities interred female and male individuals with projectile points, suggesting that large-mammal hunting may have been a gender neutral activity among that community. We report a lithic usewear analysis, which confirms that the ostensible projectile points were indeed used as projectile points. The data further reveal evidence of cutting and hide scraping consistent with animal processing activities. A new radiocarbon date shows that the female and male individuals were contemporaries, or nearly so, sometime between 9.0 and 8.7 cal. ka. These findings support a model of early subsistence practices in which both female and male individuals at Wilamaya Patjxa hunted large mammals.
The archaeology of the pre-contact Andes provides an ideal study of human responses to climate ch... more The archaeology of the pre-contact Andes provides an ideal study of human responses to climate change given the region's extreme climatic variability, excellent archaeological preservation, and robust paleoclimate records. We evaluate the effects of climate change on the frequency of interpersonal violence in the south-central Andes from ca. 1.5-0.5 ka (AD 470-1540) by comparing incidents of skeletal trauma observed among 2753 crania from 58 sites to rates of ice accumulation at the Quelccaya Glacier. We find that, in the highlands, the odds of identifying inter-personal violence increase on average by a multiplicative factor of 2.4 (1.8-3.2; 95% C.I.) for every 10-centimeter decrease in annual ice accumulation. Our statistical analysis does not detect a relationship between ice accumulation and interpersonal violence rates among coastal or mid-elevation populations. This disparity likely resulted from variable economic and sociopolitical strategies at different elevations. The failure of rain-fed agriculture during periods of drought and concomitant dissolution of organizing polities likely predisposed highland populations to socioeconomic stress and violent competition for limited resources. Conversely, diversity among lowland and midland economies may have buffered against the effect of drought.
Anthropological research has long theorized that emergent food-producing economies catalyzed high... more Anthropological research has long theorized that emergent food-producing economies catalyzed high levels of inequality in human societies, as evident in the earliest use of jewelry made from gold, copper, and other precious minerals among early agricultural populations. Although the US Southwest appears to have been an exception, we report the discovery of two Basketmaker II period necklaces constructed of green iridescent scarab beetle femora, which suggests a homologous association between emergent agriculture and inequality. Drawing insight from ethnography, archaeology, entomology, and evolutionary ecology, we hypothesize that these and other jewelry items of Basketmaker II culture were visually prominent, honest signals of socioeconomic capital that emerged during a period of surplus food production and incipient wealth accumulation. It appears that Basketmaker II societies-like other emergent food-producing economies around the worldgrappled with the opportunities and challenges that arise with surplus production, albeit in a distinct way that involved visually striking insect and feather adornments as status signals. Archaeologists may have previously overlooked this behavior due to Western biases that privilege precious metals and minerals as prestige objects and archaeological biases that tend to view insects as food or agents of site disturbance.
Archaic projectile points from the Andean Altiplano exhibit a curious trend of increasing size ov... more Archaic projectile points from the Andean Altiplano exhibit a curious trend of increasing size over time, in contrast to a well-documented size reduction throughout North America. Although a number of hypotheses exist to account for decreasing projectile-point size, there are currently no explicit explanations for increasing size. We consider several hypotheses and interrogate two techno-economic hypotheses. We posit that increasing point size compensated for lost dart momentum or accuracy that resulted from the shortening of atlatls or atlatl darts as wood became increasingly scarce on the tree-sparse Altiplano. We evaluate these hypotheses using a replicated Andean atlatl system in ballistic trials. Contrary to expectation, results show that point enlargement significantly reduces penetration depth, allowing us to confidently reject the momentum hypothesis. Point enlargement, in contrast, tentatively correlates positively with accuracy. Our experiment further shows that camelid bo...
The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for ... more The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for a proboscidean butchery site to be accepted, contemporaneous artifacts must be spatially associated with faunal remains, and there must be evidence of use of the remains. Fourteen sites in North America currently meet those criteria; at least 31 do not. While these are reasonable requirements for avoiding false positives, such an approach risks identifying false negatives—rejecting spatial associations that are systemic associations. Given the known distributions of Clovis and proboscidean sites, how likely is it that artifacts are coincidentally associated with proboscidean remains? Conversely, how many spatial associations could be unrecognized butchery sites? To answer these questions, we simulated chance associations by plotting empirically informed densities and sizes of archaeological and proboscidean sites on simulated landscapes in which people and animals are (a) uniformly distr...
Diverse theoretical perspectives suggest that place plays an important role in human behavior. On... more Diverse theoretical perspectives suggest that place plays an important role in human behavior. One recent perspective proposes that habitual and recursive use of places among humans may be an emergent property of obligate tool use by our species. In this view, the costs of tool use are reduced by preferential occupation of previously occupied places where cultural materials have been discarded. Here we use the model to generate five predictions for ethnographic mobility patterns. We then test the predictions against observations made during one month of coresidence with a residentially mobile Dukha family in the Mongolian Taiga. We show that (1) there is a strong tendency to occupy previously used camps, (2) previously deposited materials are habitually recycled, (3) reoccupation of places transcends kinship, (4) occupational hiatuses can span decades or longer, and (5) the distribution of occupation intensity among camps is highly skewed such that most camps are not intensively reo...
Proceedings of the National Academy of Sciences, 2016
Ecosystems on the verge of major reorganization—regime shift—may exhibit declining resilience, wh... more Ecosystems on the verge of major reorganization—regime shift—may exhibit declining resilience, which can be detected using a collection of generic statistical tests known as early warning signals (EWSs). This study explores whether EWSs anticipated human population collapse during the European Neolithic. It analyzes recent reconstructions of European Neolithic (8–4 kya) population trends that reveal regime shifts from a period of rapid growth following the introduction of agriculture to a period of instability and collapse. We find statistical support for EWSs in advance of population collapse. Seven of nine regional datasets exhibit increasing autocorrelation and variance leading up to collapse, suggesting that these societies began to recover from perturbation more slowly as resilience declined. We derive EWS statistics from a prehistoric population proxy based on summed archaeological radiocarbon date probability densities. We use simulation to validate our methods and show that ...
South American Contributions to World Archaeology, 2021
Nearly every part of the world witnessed the process of human sedentarization during the Holocene... more Nearly every part of the world witnessed the process of human sedentarization during the Holocene Epoch. Agriculture, circumscription, and ecological structure are among the major drivers previously proposed to account for this transition from residentially mobile to sedentary lifeways. This analysis explores an alternative mechanism, which considers the appearance of continuously occupied sites among residentially mobile (i.e., non-sedentary) individuals to be a key component in the trajectory to sedentism. Drawing insights from Archaic Period settlement patterns in the high Andes and a simple computer simulation, such "sedentary sites" are shown to be an emergent property of the interaction of two basic human behaviors-population growth and recursive mobility. Recursive mobility refers to the preferential occupation of certain places on landscapes as a result of human restructuring of environments and consequent recycling of cultural materials. The simulations reveal gradual emergence of continuously occupied sites by residentially mobile individuals, which accounts for the protracted nature sedentarization observed archaeologically. The model further offers a socioecological context for emergent residential sedentism among individuals themselves and a mechanism for plant domestication that does not require individual sedentism.
Neolithization was a complex, protracted process of domestication, sedentarization, and technolog... more Neolithization was a complex, protracted process of domestication, sedentarization, and technology change that occurred in various combinations in various times and places around the world. Understanding the causal relationships among those and other important human behaviors remains an analytical challenge. This study examines Neolithization through the lens of lithic artifact variation in the Lake Titicaca Basin, Peru. Drawing on previous lithics research, we outline a synthetic model linking changing diet, mobility, and projectile technology to predicted trends in lithic assemblages. The expectations are then compared to two large, well-dated lithic assemblages from the Titicaca Basin—one from the Middle/Late Archaic forager site of Soro Mik’aya Patjxa (8.0–6.5 cal. ka) and the other from the Terminal Archaic horticultural site of Jiskairumoko (5.2–3.4 cal. ka). We find that the strongest signal in lithic technology change is related to the introduction of archery technology. Signals for subsistence change and declining mobility are relatively weak. The results suggest an early but unconfirmed adoption of archery technology in the Terminal Archaic Period with major transitions in mobility and diet likely to have occurred subsequently in the Terminal Archaic or Formative periods. The findings are consistent with a behavioral model in which changes in projectile technology played a prominent role in the evolution of resource intensification and residential sedentism as well as resource privatization and sexual division of labor in the high Andes.
The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for ... more The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for a proboscidean butchery site to be accepted, contemporaneous artifacts must be spatially associated with faunal remains, and there must be evidence of use of the remains. Fourteen sites in North America currently meet those criteria; at least 31 do not. While these are reasonable requirements for avoiding false positives, such an approach risks identifying false negatives—rejecting spatial associations that are systemic associations. Given the known distributions of Clovis and proboscidean sites, how likely is it that artifacts are coincidentally associated with proboscidean remains? Conversely, how many spatial associations could be unrecognized butchery sites? To answer these questions, we simulated chance associations by plotting empirically informed densities and sizes of archaeological and proboscidean sites on simulated landscapes in which people and animals are (a) uniformly distributed and (b) tethered to water sources. The simulated frequencies of coincidental associations were compared to the observed frequency of co-occurrences. Our results suggest that of the 31 indeterminate empirical associations, at least 17 and as many as 26 are likely systemic associations, more than doubling previous estimates and revealing a greater role of humans in Pleistocene proboscidean exploitation than previously recognized.
How and why early hunter-gatherers expanded into the challenging environments of the Tibetan Plat... more How and why early hunter-gatherers expanded into the challenging environments of the Tibetan Plateau during the Pleistocene remain largely unexplained. The discovery of the archaeological site of Nwya Devu, characterized by lithic blade production, brings new evidence of human expansion to high elevations ca. 40-30 ka. The blade assemblage currently lacks technological antecedents in East Asia. During Marine Isotope Stage 3, the surrounding lowlands to the Plateau were dominated by a distinct type of industry broadly named "core and flake." It is suggested that the Nwya Devu blade assemblage derives from traditions in the eastern Eurasian Steppe, a clustered hub for Upper Paleolithic blade technology. In contrast to the East Asian lowlands, the Tibetan Plateau shares a number of environmental similarities with North and Central Asia such as low temperature and humidity, long winters, strong seasonality, and grassland landscapes. Blade and core-and-flake technologies tend to be associated with different environments in eastern Asia. We hypothesize that this geographic distribution indicates different sets of behavioral adaptations that map onto distinct ecozones and are relevant to human expansion to the Tibetan Plateau during Marine Isotope Stage 3. To evaluate the working model, we characterized the environmental parameters for both blade and core-and-flake technologies in eastern Asia during the period. The results show that environmental conditions on the Plateau and at the Nwya Devu site align with those of blade assemblages documented in the Eurasian Steppe and contrast with those of core-and-flake assemblages. Blade technology is strongly associated with low-temperature environments. These findings suggest that hunter-gatherers from the steppe belt may have benefited from their behaviorally adaptive advantages when moving into the highland environments of the Tibetan Plateau, 40-30 ka.
Human societies are characterized by norms that restrict selfish behavior and promote cooperation... more Human societies are characterized by norms that restrict selfish behavior and promote cooperation. The oxytocin system is an important modulator of social behavior that may be involved in the evolution of cooperation. Oxytocin acts in both the nucleus accumbens and the anterior cingulate cortex to promote social bonding and social cohesion. Expression of the CD38 and OXTR genes is known to affect oxytocin secretion and binding, respectively, in these brain areas. The Andean highlands provide an excellent opportunity to evaluate the role of oxytocin in the evolution of cooperation. The rich archeological record spans 13,000 years of population growth and cooperative challenges through periods of highland exploration, hunting economies, agro-pastoralism, and urbanization. Through allele trajectory modeling using both ancient and contemporary whole genomes, we find evidence for strong positive selection on the OXTR and CD38 alleles linked with increased oxytocin signaling. These selection events commenced around 2.5 and 1.25 thousand years ago, placing them in the region's Upper Formative and Tiwanaku periods-a time of population growth, urbanization, and relatively low rates of violence. Along with remarkable and enduring cultural developments, increased oxytocin secretion and receptor binding in these brain areas may have facilitated large-scale cooperation that promoted early urbanization in the Titicaca Basin of the Andean highlands.
Satellite survey is widely used for archaeological site discovery, but the efficacy of the method... more Satellite survey is widely used for archaeological site discovery, but the efficacy of the method has received little systematic investigation. In this analysis, twelve study participants of different experience levels performed an unstructured remote survey of 197 km 2 in the Sama and Moquegua valleys of south central Peru where previous pedestrian surveys recorded 546 archaeological sites. Results indicate an average site discovery rate of 9.3% (0-18%, 95% range). The most experienced participants detect up to 20% (17-22%) of known archaeological sites. These detection rates can be used to derive reliable site frequency estimates on the Andean coast, which can be used in planning and budgeting for field efforts and estimating demographic patterns at large spatial scales that are difficult to achieve through pedestrian survey. More generally, this analysis offers a method for deriving correction terms specific to other parts of the world. Additionally, the results can serve as a baseline for evaluating the effectiveness of emerging artificial intelligence routines for archaeological site detection.
Neolithization was a complex, protracted process of domestication, sedentarization, and technolog... more Neolithization was a complex, protracted process of domestication, sedentarization, and technology change that occurred in various combinations in various times and places around the world. Understanding the causal relationships among those and other important human behaviors remains an analytical challenge. This study examines Neolithization through the lens of lithic artifact variation in the Lake Titicaca Basin, Peru. Drawing on previous lithics research, we outline a synthetic model linking changing diet, mobility, and projectile technology to predicted trends in lithic assemblages. The expectations are then compared to two large, well-dated lithic assemblages from the Titicaca Basin—one from the Middle/Late Archaic forager site of Soro Mik’aya Patjxa (8.0–6.5 cal. ka) and the other from the Terminal Archaic horticultural site of Jiskairumoko (5.2–3.4 cal. ka). We find that the strongest signal in lithic technology change is related to the introduction of archery technology. Sig...
Current models of early human subsistence economies suggest a focus on large mammal hunting. To e... more Current models of early human subsistence economies suggest a focus on large mammal hunting. To evaluate this hypothesis, we examine human bone stable isotope chemistry of 24 individuals from the early Holocene sites of Wilamaya Patjxa (9.0–8.7 cal. ka) and Soro Mik’aya Patjxa (8.0–6.5 cal. ka) located at 3800 meters above sea level on the Andean Altiplano, Peru. Contrary to expectation, Bayesian mixing models based on the isotope chemistry reveal that plants dominated the diet, comprising 70–95% of the average diet. Paleoethnobotanical data further show that tubers may have been the most prominent subsistence resource. These findings update our understanding of earliest forager economies and the pathway to agricultural economies in the Andean highlands. The findings furthermore suggest that the initial subsistence economies of early human populations adapting to new landscapes may have been more plant oriented than current models suggest.
Oxford Research Encyclopedia of Anthropology, 2023
The Andean highlands of western South America spans 7,000 km from the equator to Patagonia and re... more The Andean highlands of western South America spans 7,000 km from the equator to Patagonia and reaches altitudes of 7,000 m. Extreme cold, hypoxia, and low bioproductivity impose a distinct set of challenges to human survival and reproduction. This adaptive setting has inspired considerable archaeological and genetic research, which seeks to define the timing and nature of the adaptive process. Current evidence establishes that Paleoindian populations with fluted-point projectile technology first entered the highlands around 12.8 cal. ka. Paleoindian use of the highlands over the subsequent one thousand years appears to have been ephemeral. During the Early Archaic period (11.7–9.0 cal. ka), a culturally and genetically distinct population appears to have replaced the Paleoindian population in the highlands where they eventually established year-round settlement systems. Early Archaic cultural adaptations included large-mammal hunting, tuber foraging, animal-hide technology, logistical mobility, and egalitarian social structure. Potential genetic adaptations include selection for respiratory and cardiovascular strength and enhanced starch digestion capacity. Human adaptation to the Andean highlands thus appears to have been a multifaceted process that transpired over some four thousand years. Although current evidence favors a model of gradual adaptation, a more rapid adaptive process cannot yet be excluded. Paleoindian sites remain woefully sparse, which may indicate limited use or a sampling problem. And although recent genetic and isotopic analyses have been incisive, they are restricted to few samples from relatively late contexts. Continued investigations at the intersection of traditional archaeological methods and new biomolecular methods are likely to resolve outstanding questions soon and create opportunities to explore more-nuanced questions about the peopling of the high Andes.
The extent to which archery technology affected social organization in the Andes region of South ... more The extent to which archery technology affected social organization in the Andes region of South America remains understudied. To identify the timing and consequences of archery technology in the Lake Titicaca Basin, this analysis examines metric data from 1179 projectile points from the region, 11-1.0 cal. ka. We find that the greatest decrease in projectile point size occurred across the Late/Terminal Archaic and Formative/Tiwanaku period boundaries, 5.0 and 1.5 cal. ka, respectively. We do not find a statistically significant decrease in size during any other transition, including the Terminal Archaic/Formative boundary, which was previously hypothesized to have been the time when archery technology first appeared in the region. These results instead favor the hypothesis that archery technology first entered the region during the Terminal Archaic Period, 5.0-3.5 cal ka. We furthermore observe that this technological transition coincided with the growth of settlements, a surge in the use of exotic goods such as obsidian, a low level of inter-group violence, and incipient agropastoralism-a pattern that intensified during the subsequent Formative period when monumental ceremonial centers emerged. These findings lead us to propose a model for South American archery technology in which its appearance after 5000 years ago contributed to the emergence of new cooperative dynamics that expanded regional exchange networks and community aggregation.
Approximately 9000 years ago at the Andean highland site of Wilamaya Patjxa, forager communities ... more Approximately 9000 years ago at the Andean highland site of Wilamaya Patjxa, forager communities interred female and male individuals with projectile points, suggesting that large-mammal hunting may have been a gender neutral activity among that community. We report a lithic usewear analysis, which confirms that the ostensible projectile points were indeed used as projectile points. The data further reveal evidence of cutting and hide scraping consistent with animal processing activities. A new radiocarbon date shows that the female and male individuals were contemporaries, or nearly so, sometime between 9.0 and 8.7 cal. ka. These findings support a model of early subsistence practices in which both female and male individuals at Wilamaya Patjxa hunted large mammals.
The archaeology of the pre-contact Andes provides an ideal study of human responses to climate ch... more The archaeology of the pre-contact Andes provides an ideal study of human responses to climate change given the region's extreme climatic variability, excellent archaeological preservation, and robust paleoclimate records. We evaluate the effects of climate change on the frequency of interpersonal violence in the south-central Andes from ca. 1.5-0.5 ka (AD 470-1540) by comparing incidents of skeletal trauma observed among 2753 crania from 58 sites to rates of ice accumulation at the Quelccaya Glacier. We find that, in the highlands, the odds of identifying inter-personal violence increase on average by a multiplicative factor of 2.4 (1.8-3.2; 95% C.I.) for every 10-centimeter decrease in annual ice accumulation. Our statistical analysis does not detect a relationship between ice accumulation and interpersonal violence rates among coastal or mid-elevation populations. This disparity likely resulted from variable economic and sociopolitical strategies at different elevations. The failure of rain-fed agriculture during periods of drought and concomitant dissolution of organizing polities likely predisposed highland populations to socioeconomic stress and violent competition for limited resources. Conversely, diversity among lowland and midland economies may have buffered against the effect of drought.
Anthropological research has long theorized that emergent food-producing economies catalyzed high... more Anthropological research has long theorized that emergent food-producing economies catalyzed high levels of inequality in human societies, as evident in the earliest use of jewelry made from gold, copper, and other precious minerals among early agricultural populations. Although the US Southwest appears to have been an exception, we report the discovery of two Basketmaker II period necklaces constructed of green iridescent scarab beetle femora, which suggests a homologous association between emergent agriculture and inequality. Drawing insight from ethnography, archaeology, entomology, and evolutionary ecology, we hypothesize that these and other jewelry items of Basketmaker II culture were visually prominent, honest signals of socioeconomic capital that emerged during a period of surplus food production and incipient wealth accumulation. It appears that Basketmaker II societies-like other emergent food-producing economies around the worldgrappled with the opportunities and challenges that arise with surplus production, albeit in a distinct way that involved visually striking insect and feather adornments as status signals. Archaeologists may have previously overlooked this behavior due to Western biases that privilege precious metals and minerals as prestige objects and archaeological biases that tend to view insects as food or agents of site disturbance.
Archaic projectile points from the Andean Altiplano exhibit a curious trend of increasing size ov... more Archaic projectile points from the Andean Altiplano exhibit a curious trend of increasing size over time, in contrast to a well-documented size reduction throughout North America. Although a number of hypotheses exist to account for decreasing projectile-point size, there are currently no explicit explanations for increasing size. We consider several hypotheses and interrogate two techno-economic hypotheses. We posit that increasing point size compensated for lost dart momentum or accuracy that resulted from the shortening of atlatls or atlatl darts as wood became increasingly scarce on the tree-sparse Altiplano. We evaluate these hypotheses using a replicated Andean atlatl system in ballistic trials. Contrary to expectation, results show that point enlargement significantly reduces penetration depth, allowing us to confidently reject the momentum hypothesis. Point enlargement, in contrast, tentatively correlates positively with accuracy. Our experiment further shows that camelid bo...
The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for ... more The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for a proboscidean butchery site to be accepted, contemporaneous artifacts must be spatially associated with faunal remains, and there must be evidence of use of the remains. Fourteen sites in North America currently meet those criteria; at least 31 do not. While these are reasonable requirements for avoiding false positives, such an approach risks identifying false negatives—rejecting spatial associations that are systemic associations. Given the known distributions of Clovis and proboscidean sites, how likely is it that artifacts are coincidentally associated with proboscidean remains? Conversely, how many spatial associations could be unrecognized butchery sites? To answer these questions, we simulated chance associations by plotting empirically informed densities and sizes of archaeological and proboscidean sites on simulated landscapes in which people and animals are (a) uniformly distr...
Diverse theoretical perspectives suggest that place plays an important role in human behavior. On... more Diverse theoretical perspectives suggest that place plays an important role in human behavior. One recent perspective proposes that habitual and recursive use of places among humans may be an emergent property of obligate tool use by our species. In this view, the costs of tool use are reduced by preferential occupation of previously occupied places where cultural materials have been discarded. Here we use the model to generate five predictions for ethnographic mobility patterns. We then test the predictions against observations made during one month of coresidence with a residentially mobile Dukha family in the Mongolian Taiga. We show that (1) there is a strong tendency to occupy previously used camps, (2) previously deposited materials are habitually recycled, (3) reoccupation of places transcends kinship, (4) occupational hiatuses can span decades or longer, and (5) the distribution of occupation intensity among camps is highly skewed such that most camps are not intensively reo...
Proceedings of the National Academy of Sciences, 2016
Ecosystems on the verge of major reorganization—regime shift—may exhibit declining resilience, wh... more Ecosystems on the verge of major reorganization—regime shift—may exhibit declining resilience, which can be detected using a collection of generic statistical tests known as early warning signals (EWSs). This study explores whether EWSs anticipated human population collapse during the European Neolithic. It analyzes recent reconstructions of European Neolithic (8–4 kya) population trends that reveal regime shifts from a period of rapid growth following the introduction of agriculture to a period of instability and collapse. We find statistical support for EWSs in advance of population collapse. Seven of nine regional datasets exhibit increasing autocorrelation and variance leading up to collapse, suggesting that these societies began to recover from perturbation more slowly as resilience declined. We derive EWS statistics from a prehistoric population proxy based on summed archaeological radiocarbon date probability densities. We use simulation to validate our methods and show that ...
South American Contributions to World Archaeology, 2021
Nearly every part of the world witnessed the process of human sedentarization during the Holocene... more Nearly every part of the world witnessed the process of human sedentarization during the Holocene Epoch. Agriculture, circumscription, and ecological structure are among the major drivers previously proposed to account for this transition from residentially mobile to sedentary lifeways. This analysis explores an alternative mechanism, which considers the appearance of continuously occupied sites among residentially mobile (i.e., non-sedentary) individuals to be a key component in the trajectory to sedentism. Drawing insights from Archaic Period settlement patterns in the high Andes and a simple computer simulation, such "sedentary sites" are shown to be an emergent property of the interaction of two basic human behaviors-population growth and recursive mobility. Recursive mobility refers to the preferential occupation of certain places on landscapes as a result of human restructuring of environments and consequent recycling of cultural materials. The simulations reveal gradual emergence of continuously occupied sites by residentially mobile individuals, which accounts for the protracted nature sedentarization observed archaeologically. The model further offers a socioecological context for emergent residential sedentism among individuals themselves and a mechanism for plant domestication that does not require individual sedentism.
Neolithization was a complex, protracted process of domestication, sedentarization, and technolog... more Neolithization was a complex, protracted process of domestication, sedentarization, and technology change that occurred in various combinations in various times and places around the world. Understanding the causal relationships among those and other important human behaviors remains an analytical challenge. This study examines Neolithization through the lens of lithic artifact variation in the Lake Titicaca Basin, Peru. Drawing on previous lithics research, we outline a synthetic model linking changing diet, mobility, and projectile technology to predicted trends in lithic assemblages. The expectations are then compared to two large, well-dated lithic assemblages from the Titicaca Basin—one from the Middle/Late Archaic forager site of Soro Mik’aya Patjxa (8.0–6.5 cal. ka) and the other from the Terminal Archaic horticultural site of Jiskairumoko (5.2–3.4 cal. ka). We find that the strongest signal in lithic technology change is related to the introduction of archery technology. Signals for subsistence change and declining mobility are relatively weak. The results suggest an early but unconfirmed adoption of archery technology in the Terminal Archaic Period with major transitions in mobility and diet likely to have occurred subsequently in the Terminal Archaic or Formative periods. The findings are consistent with a behavioral model in which changes in projectile technology played a prominent role in the evolution of resource intensification and residential sedentism as well as resource privatization and sexual division of labor in the high Andes.
The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for ... more The extent to which Clovis peoples hunted proboscideans is debated. Convention requires that for a proboscidean butchery site to be accepted, contemporaneous artifacts must be spatially associated with faunal remains, and there must be evidence of use of the remains. Fourteen sites in North America currently meet those criteria; at least 31 do not. While these are reasonable requirements for avoiding false positives, such an approach risks identifying false negatives—rejecting spatial associations that are systemic associations. Given the known distributions of Clovis and proboscidean sites, how likely is it that artifacts are coincidentally associated with proboscidean remains? Conversely, how many spatial associations could be unrecognized butchery sites? To answer these questions, we simulated chance associations by plotting empirically informed densities and sizes of archaeological and proboscidean sites on simulated landscapes in which people and animals are (a) uniformly distributed and (b) tethered to water sources. The simulated frequencies of coincidental associations were compared to the observed frequency of co-occurrences. Our results suggest that of the 31 indeterminate empirical associations, at least 17 and as many as 26 are likely systemic associations, more than doubling previous estimates and revealing a greater role of humans in Pleistocene proboscidean exploitation than previously recognized.
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