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La jerarquización de recursos constituye uno de los procedimientos más empleados para evaluar la subsistencia de los cazadores-recolectores en el pasado. Para el Centro Occidente Argentino (COA) esta jerarquización se fundaba en el tamaño corporal de las presas. Aquí incorporamos datos sobre los costos de manejo, generando el primer ordenamiento de recursos para la región que contempla los elementos requeridos por los modelos de optimización (Kcal/tiempo post-encuentro). Luego del guanaco (Lama guanicoe) —presa de mayor rendimiento— este ranking situó en segundo y tercer lugar a los huevos de Rheidae y los armadillos (Dasypodidae), respectivamente, resaltando la importancia de presas tradicionalmente consideradas de bajo rendimiento. Siguiendo la teoría de aprovisionamiento óptimo, elaboramos el modelo de amplitud de dieta (MAD) para los desiertos más representativos de Nordpatagonia: el de Monte y el patagónico. En este último, la mayor disponibilidad de guanacos tornó menos ventajosa la incorporación de nuevos ítems a la dieta. Para el Monte, la dieta óptima se amplió, incluyendo recursos menores como ciertos peces (i.e., Percichthys trucha). En definitiva, el MAD permitió reinterpretar tendencias temporales en la subsistencia humana, sosteniendo una ampliación en el espectro de recursos explotados hacia el Holoceno tardío en el COA. En general, las expectativas del MAD son confirmadas con el registro zooarqueológico regional.

Storage has long been recognized as critical to understanding the behavior and cultural evolution of hunting and gathering communities living at mid-latitudes throughout the world. Storage is a complex and powerful strategy, with profound results for human behavior and evolutionary consequences such as sedentism and population growth, increased sociopolitical complexity, social inequality, and the development of agriculture. One of the more provocative aspects of storage is how it may influence territorial behavior and defense tactics in human societies - a question that has been given little attention. In this paper we present a model of storage defense and suggest a simple notion: that storage defense territoriality is expected when the cost of defending stores is less than the cost of losing them. The cost-benefit dynamics of defending stored food are critically influenced by seasonality and storage (front-back loaded) timing. Territoriality in western North America developed along two fundamentally different evolutionary trajectories: expansive territorialism and intensive territorialism, which influence rational choice and socio-political developments. Expansive territorialism involves higher level decision making which incentivizes greater physical risk tied to territorial expansion and defense, whereas intensive territorialism involves inward turned interests that incentivize drudgery. Empirical evidence supports the notion that at the time of European contact intensive territorialism was the more common strategy followed by groups in California and much of the Pacific Northwest Coast. In contrast, some distinct Pacific Northwest groups were set along expansive territorial trajectories. These trajectories profoundly influence diet choice and territorial strategizing: Expansive Northwest Coast groups are heavily engaged in raiding and territorial expansion and rely more on front-loaded fish and marine mammals than do non-expansive Northwest Coast or northwestern California groups, who instead of raiding and poaching the front-loaded resources of their neighbors, turn intensification inward, supporting themselves in ever-smaller areas by emphasizing the use of back-loaded plant resources.

The Paleolithic record of the southwestern Ordos Loop region of northwestern China suggests settlement variability, increased occupational intensity, and the intrusion or development of blade-based technology ca. 41,000–37,000 cal BP. These phenomena are also associated with equivocal evidence for ornamentation. More substantial changes in hominin behavior, however, are evident during and immediately after the Last Glacial Maximum (LGM), this marked by the development or intrusion of microblade technologies, perhaps groundstone technologies, and reductions in hominin population density. While changes in technology and settlement at approximately 40,000 cal BP arguably equate with some qualitative descriptors of modern human behavior and are contemporaneous with some estimates for the arrival of anatomically modern humans in the region, at present it is unclear whether these changes represent the expression of truly modern human behaviors. In part, this is because the East Asian Paleolithic record is so different from Europe and Africa and because the critical changes leading to the unequivocally modern human behaviors of the Terminal Pleistocene and Early Holocene appeared fairly late, during the LGM. Consequently, we argue that the LGM provided the environment of selection for modern human behaviors in northwestern China, whether their origins were ultimately the result of immigration, diffusion, in situ development, or some combination thereof.

This article provides a theoretical treatment of hunter-gatherer diet and physiology. Through a synthesis of nutritional studies, informed by ethno-archaeological data, we examine the risk of protein-rich diets for human survival, and how societies circumvent "salmon starvation" in the northeastern Pacific Rim. Fundamental nutritional constraints associated with salmon storage and consumption counter long-standing assumptions about the engine of cultural evolution in the region. Excess consumption of lean meat can lead to protein poisoning, termed by early explorers "rabbit starvation." While consumption of fats and carbohydrates is widely portrayed as a pathway to "offsetting" protein thresholds, there are true limits to the amount of protein individuals can consume, and constraints are most extreme for smaller individuals, children, and pregnant/nursing mothers. While this problem is not usually perceived as associated with fish, the risk of protein poisoning limits the amount of low-fat fish that people can eat safely. Compared with smaller, mass-harvested species (e.g., eulachon), dried salmon are exceedingly lean. Under certain circumstances fattier foods (small forage fish, marine mammals, whales, and even bears) or carbohydrate-rich plants may have been preferred not just for taste but to circumvent this "dietary protein ceiling." Simply put, "salmon specialization" cannot evolve without access to complimentary caloric energy through fat-rich or carbohydrate-rich resources. By extension, the evolution of storage-based societies requires this problem be solved prior to or in tandem with-salmon intensification. Without such solutions, increased mortality and reproductive rates would have made salmon reliance unsustainable. This insight is in line with genomic research suggesting protein toxicity avoidance was a powerful evolutionary force, possibly linked to genetic adaptations among First Americans. It is also relevant to evaluating the plausibility of other purportedly "focal" economies and informs understanding of the many solutions varied global societies have engineered to overcome physiological protein limits.

A regional approach to the archaeological record—one that includes not only large, stratified sites, but also small, ephemeral ones, surface finds, and isolates—provides a more representative sample of prehistoric landscape use than do stratified sites alone. In southern Mendoza Province, Argentina the stratified site record suggests both demographic decline during the middle Holocene (8000–4000 BP) and infrequent use of a vast plain east of the Andes until approximately 2000 years BP. However, results of a large-scale surface survey and obsidian geochemical and hydration analyses indicate further assessment of both trends is warranted. Specifically, our data suggest both continuous occupation of the region and use of the plains throughout the Holocene. These results have important implications for both local-scale human ecology, and broader adaptive responses to environmental changes in semi-arid southern South America.

The theoretical basis for understanding how human forager mobility should respond to environmental change rests on two models: patch choice and the marginal value theorem. Students of hunter–gatherers have traditionally understood the more widely favored marginal value theorem to predict that use of a given patch will be more intensive, i.e., that a greater fraction of its resources will be used, when overall (environmental) return rate decreases. We show this is true only if that patch is less affected by resource decrease than others in the environment, in the simplest case, where the number of patches available to a forager decreases without affecting the quality of the remaining patches. Then, foraging time within the patch, fraction of patch resources used, and travel time between patches will all increase. Conversely, if resources decrease across all patches uniformly, the fraction of patch resources extracted from any given patch remains constant. Within-patch foraging time may or may not decrease, but will not increase. In this case, foraging time varies independently of fraction of patch resources used and travel time. The extent to which these marginal value predictions account for hunter–gatherer mobility requires disentangling them from predictions independently generated by the patch choice model, in which as environmental quality declines, lower ranking patches are added to the foraging itinerary, decreasing travel time and either increasing or decreasing foraging time, depending on the nature of the lower ranking patches. A sample of 190 mobile hunter–gatherers suggests that a version of the patch choice model in which the patches added to the foraging itinerary are more difficult to search, and contain greater quantities of resources with higher handling times, best accounts for observed variation in foraging and travel time overall.

At the global scale, conceptions of hunter-gatherer economies have changed considerably over time and these changes were strongly affected by larger trends in Western history, philosophy, science, and culture. Seen as either “savage” or “noble” at the dawn of the Enlightenment, hunter-gatherers have been regarded as everything from holdovers from a basal level of human development, to affluent, ecologically-informed foragers, and ultimately to this: an extremely diverse economic orientation entailing the fullest scope of human behavioral diversity. The only thing linking studies of hunter-gatherers over time is consequently simply the definition of the term: people whose economic mode of production centers on wild resources. When hunter-gatherers are considered outside the general realm of their shared subsistence economies, it is clear that their behavioral diversity rivals or exceeds that of other economic orientations. Hunter-gatherer behaviors range in a multivariate continuum from: a focus on mainly large fauna to broad, wild plant-based diets similar to those of agriculturalists; from extremely mobile to sedentary; from relying on simple, generalized technologies to very specialized ones; from egalitarian sharing economies to privatized competitive ones; and from nuclear family or band-level to centralized and hierarchical decision-making. It is clear, however, that hunting and gathering modes of production had to have preceded and thus given rise to agricultural ones. What research into the development of human economies shows is that transitions from one type of hunting and gathering to another, or alternatively to agricultural modes of production, can take many different evolutionary pathways. The important thing to recognize is that behaviors which were essential to the development of agriculture—landscape modification, intensive labor practices, the division of labor and the production, storage, and redistribution of surplus—were present in a range of hunter-gatherer societies beginning at least as early as the Late Pleistocene in Africa, Europe, Asia, and the Americas. Whether these behaviors eventually led to the development of agriculture depended in part on the development of a less variable and CO2-rich climatic regime and atmosphere during the Holocene, but also a change in the social relations of production to allow for hoarding privatized resources. In the 20th and 21st centuries, ethnographic and archaeological research shows that modern and ancient peoples adopt or even revert to hunting and gathering after having engaged in agricultural or industrial pursuits when conditions allow and that macroeconomic perspectives often mask considerable intragroup diversity in economic decision making: the pursuits and goals of women versus men and young versus old within groups are often quite different or even at odds with one another, but often articulate to form cohesive and adaptive economic wholes. The future of hunter-gatherer research will be tested by the continued decline in traditional hunting and gathering but will also benefit from observation of people who revert to or supplement their income with wild resources. It will also draw heavily from archaeology, which holds considerable potential to document and explain the full range of human behavioral diversity, hunter-gatherer or otherwise, over the longest of timeframes and the broadest geographic scope.

The identification and dating of South Temple Canyon 1 (STC 1), an Early Upper Paleolihic (EUP) site in north-central China near Shuidonggou (SDG), helps confirm that SDG is one of the earliest EUP sites in northern Asia. Materials from STC 1 bear a strong resemblance to the early SDG core-and-blade lithic technology that includes flat-faced cores and elongate blades. We obtained a 14C age estimate of 41,070 ± 890 14C yr BP on the innermost lamina of a calcium carbonate pendant attached to one of the quartzite flakes from the site. The purity of the micrite lamina, the care taken in obtaining the carbonate sample for processing and dating, and the geomorphological setting from which the flake came suggest the age estimate represents a reasonable assessment of an accurate minimum age for STC 1. Together with recently derived age estimates of >35 14C ka for the initial EUP occupations at SDG 1 and 2, it appears that the EUP in the SDG area is as old as any of the handful of EUP sites in Mongolia and Siberia dating to about 40 14C ka, and brings into question a postulated north-to-south spread of the EUP lithic technology present at SDG. Whether or not the dispersal of this technology is associated with the spread of Anatomically Modern Humans remains unknown.

The effect of rapid climate change during the Late Upper Paleolithic on hunter-gatherers is attested by a variety of signals in the archaeological record. One of these, the spread of the microblade technology in North China, shows a particularly close relationship with climate change. The appearance of microblades and functionally related bone and ground stone technology at SDG12 is particularly revealing of this Late Pleistocene adaptive diversification in North China. SDG12 and other records suggest that microblade technology flourished in harsh environments that demanded high residential mobility. That in addition to their use in hunting weaponry, microblades were used in manufacturing the sophisticated cold weather clothing required for winter mobility, is shown by the presence of bone needles and a bone knife handle slotted to accept microblades. The SDG12 fauna and ground stone indicate an attendant shift from a more large game dominated, to a more plant and small game dominated diet that included net hunting and demanded a variety of production tasks that included net-making (spinning) and extensive stone boiling to maximize nutrient returns and as a step in manufacturing. We suspect these changes are the root cause of subsequent changes in social structure.

Among the many useful yardsticks of evolutionary success, trajectory of population growth is perhaps the most telling, and it is the focus on this metric that makes the contribution by Zahid et al. (1) in PNAS so compelling. They document hunter–gatherer population growth between 13,000 and 6,000 y ago in the western US states of Wyoming and Colorado, in doing so showing (i) that reliable population trajectories can be obtained through careful analysis of the radiocarbon record, and (ii) that the Wyoming-Colorado hunter–gatherers they studied achieved long-term rates of population growth comparable to the rates of population growth achieved by prehistoric New and Old World agriculturalists, and (iii) they proceed on the basis of this and other evidence to generalize that contrary to received wisdom, prehistoric hunter–gatherers consistently achieved long-term growth rates equivalent to the growth rates of prehistoric agriculturalists. These findings raise a multitude of interesting questions regarding the transition from hunting and gathering to agriculture, particularly why, without enjoying any competitive advantage in rate of population growth, agriculture was so consistently able replace hunting and gathering worldwide during the Holocene.

A review of recently published temporal data from Shuidonggou Locality 1 indicates that a 40–43 cal ka date for the inception of Initial Upper Paleolithic (IUP) blade-oriented technologies in East Asia is warranted. Comparison of the dates from Shuidonggou to other Asian IUP dates in Korea, Siberia, and Mongolia supports this assertion, indicating that the initial appearance of the IUP in East Asia generally corresponds in time to the fluorescence of the IUP in eastern Europe and western Asia. This conclusion preliminarily suggests that either a version of the IUP originated independently in East Asia just prior to 40 cal ka, or more likely, that an early, initial diffusion of the IUP into East Asia occurred ~41 cal ka, a hypothesis consistent with current estimates for the evolution or arrival of modern humans in the region. DOI: 10.2458/56.16270

Despite the enormous potential of anadromous fish, foragers do not mass extract and store salmonids until very late in the archaeological record of California. Acorns, by contrast, were intensively used quite early in the record. Salmon are traditionally viewed as a low cost, high ranking resource, and acorns as a high cost, low ranking resource. The question thus arises: why were salmon not used and stored en masse much earlier? We offer a solution using a simple foraging model that distinguishes resources on their storage as well as overall cost, making it possible to calculate the risk of resource caching, which appears to have delayed intensive salmon procurement in California.

Though present before the Last Glacial Maximum, microblade technology is uncommon in the lithi c assembla ges of north-central China until the onset of the Younger Dryas (12,900–11,600 calBP). While it is clear that microblades here and elsewhere were connected with mobile adaptations organized around hunting, the attendant assumption that they served primarily in hunting weaponry is not. The archaeol ogical record of north-central China, including excavations at Pigeon Mountain (QG3) and Shuidonggou Locality 12 (SDG 12) in Ningx ia Autonomous Region, and Dadiwan in Gansu Providence, and a handful of bone/antler tools slotted for microblade inserts, indicate a more direct linkage to mobility. These data suggest the rise of microblade technology in Younger Dryas north-central China was mainly the result of microblades used as insets in composite knives needed for production of sophisticated cold weather clothing needed for a winter mobile hunting adaptation akin to the residentially mobile pattern Binford termed ‘‘serial specialist.’’ Limited time and opportunities compressed this production into a very narrow seasonal window, putting a premium on highly streamlined routines to which mic roblade technology was especially well-suited.

The bow more than doubled, likely tripled, the success of individuals bent on killing animal or human targets (Box 1). The advent of this revolutionary technology generated different responses in western North America depending on subsistence and sociopolitical organization at the time of its arrival, roughly 2300 - 1300 B.P.[1] Its effect was substantial in California and the Great Basin, particularly on group size, which in many places diminished as a consequence of the bow's reliability. The counter-intuitive result was to increase within group-relatedness enough to encourage intensification of plant resources, previously considered too costly. The bow rose to greatest direct economic importance with the arrival of the horse, and was put to most effective use by former Great Basin groups who maintained the family band system that had developed around intensive Great Basin plant procurement, adapting the same organization to a lifestyle centered on the equestrian pursuit of buffalo and warfare.

The origin of human violence and warfare is controversial, and some scholars contend that intergroup conflict was rare until the emergence of sedentary foraging and complex sociopolitical organization, whereas others assert that violence was common and of considerable antiquity among small-scale societies. Here we consider two alternative explanations for the evolution of human violence: (i) individuals resort to violence when benefits outweigh potential costs, which is likely in resource poor environments, or (ii) participation in violence increases when there is coercion from leaders in complex societies leading to group level benefits. To test these hypotheses, we evaluate the relative importance of resource scarcity vs. sociopolitical complexity by evaluating spatial variation in three macro datasets from central California: (i) an extensive bioarchaeological record dating from 1,530 to 230 cal BP recording rates of blunt and sharp force skeletal trauma on thousands of burials, (ii) quantitative scores of sociopolitical complexity recorded ethnographically, and (iii) mean net primary productivity (NPP) from a remotely sensed global dataset. Results reveal that sharp force trauma, the most common form of violence in the record, is better predicted by resource scarcity than relative sociopolitical complexity. Blunt force cranial trauma shows no correlation with NPP or political complexity and may reflect a different form of close contact violence. This study provides no support for the position that violence originated with the development of more complex hunter-gatherer adaptations in the fairly recent past. Instead, findings show that individuals are prone to violence in times and places of resource scarcity.

Intensive research on China's Western Loess Plateau has located 63 Palaeolithic deposits, which together allow the authors to present a general model of hominin occupation from 80 000 to 18 000 years ago. Tools, subsistence and settlement correlate nicely with the climate: the warm wet MIS3 seeing expansion and more organised acquisition of quartz, and the Late Glacial Maximum that followed, a reduction in human presence but possibly an increase in ingenuity.

The paper examines Middle Holocene hunter-gatherer adaptive strategies in the Baikal region of Siberia based on diverse data (radiocarbon, mortuary, geochemical, genetic, human osteological, and zooarchaeological) accumulated over the last 10–15 years. The new model emphasizes the cyclical nature of the long-term changes and recognizes similarities between the Early Neolithic and Late Neolithic–Early Bronze Age cultures. The overall impression seems to be that change in the region was rapid rather than gradual. A number of interesting correlations between various cultural and environmental variables have been identified. During the Early Neolithic and Late Neolithic–Bronze Age, the spatial distributions of mortuary sites, open landscape, and good fisheries are all correlated and both intervals are coeval with periods of environmental stability. For the Early Neolithic two additional sets of correlated variables have been identified: (1) the uneven distribution of fish resources, uneven distribution of the human population, and cultural heterogeneity; and (2) poorer overall community health, more extensive male travel and heavier workloads, and higher reliance on fishing. For the Late Neolithic–Early Bronze Age, the sets of correlated variables are somewhat different: (1) more even distribution of terrestrial game resources (herbivores), more even distribution of the human population, and cultural homogeneity; and (2) better overall community health, less travel and lighter workloads, more equitable distribution of labor between males and females, and higher reliance on game hunting. Viewed together, these patterns emphasize the much more dynamic pattern of hunter-gatherer cultural variability, temporally and spatially, compared to what was known before.

Recent excavations at the Dadiwan site in the western Loess Plateau, Gansu Province, People’s Republic of China (PRC), document the first continuous foraging-to-farming sequence in North China. The Dadiwan occupation began at about 80,000 BP and became regular by about 60,000 BP, probably before the arrival or evolution of modern Homo sapiens in North China. This record spans the transitions from nonintensive to intensive hunting and gathering and from intensive hunting and gathering to low-level Laoguantai food production and finally intensive Late Banpo, Neolithic agriculture. The intensive hunter-gatherer adaptation from which Dadiwan millet agriculture evolved did not develop at Dadiwan itself. Instead, it came south with intensive hunter-gatherer groups migrating out of the arid deserts north of the Yellow River, where the late Pleistocene–early Holocene North China Microlithic was common.

This paper reports the recent excavation of Unit Dadiwan06 at the Dadiwan site in Qin’an County, Gansu. A 65 ka chronological framework is established for Dadiwan06 on the basis of absolute dating (AMS 14C and OSL), stratigraphy, climate change events and archaeology. Artifact distributions reveal patterns of human behavioral variation and adaptation over the past 60 ka, from primitive hunting and gathering to advanced hunting and gathering, to primitive Neolithic agriculture, and finally to advanced Neolithic agriculture.

Key trends in California prehistory diverge from those characteristic of other world regions; sophisticated advances in the application of human behavioral ecology to archaeological interpretation help us to understand why. Significant interpretive advances have been stimulated by the on-going "provisioning" versus "costly signaling" debate. We argue that provisioning currently has the upper hand because the diet breadth model is older, better understood, and more easily assessed in light of archaeological data than is costly signaling. Archaeological research outside of California will need to confront issues of provisioning and prestige in their own empirical context and in light of behavioral ecology methods developed here. Las tendencias clave en la prehistoria de California se separan de esas caracteristicas en otras regiones del mundo; avances sofisticados en la aplicacion de la ecologia de la conducta humana a la interpretacion arqueologica nos ayudan a comprender por que. El debat...

The development of agriculture was limited by external constraints, mainly climate, before the Holocene and mainly by social institutions after that. Population size and growth was important but ultimately did not determine where and why agriculture evolved.

Obsidian is abundant in archaeological sites throughout Mendoza Province, Argentina but no obsidian hydration rates exist to date these assemblages. Direct dating of obsidian artifacts is particularly important in west-central Argentina because the surface record is extensive but well-defined time marker artifacts are lacking. The costs of non-optical hydration dating techniques currently preclude their regular use in the region, however. We present and evaluate 12 models for age estimation based on optical hydration rim measurements for the two most commonly used obsidian types in the region (Las Cargas and Laguna del Maule). Age estimation equations are derived for each source using observed hydration rim-radiocarbon date pairs, and parameterized by variables known to influence obsidian hydration in experimental settings. The equations advanced here are currently best at predicting the known ages of artifacts independently dated by radiocarbon, and can be cautiously used to estimate the ages of obsidian artifacts. Las obsidianas son abundantes en los sitios arqueológicos de la provincia de Mendoza (Argentina). Sin embargo, hasta el momento no existen estimaciones para las tasas de hidratación de estas rocas que puedan utilizarse para fechar esos conjuntos líticos. La realización de fechados directos sobre artefactos de obsidiana resulta particularmente importante para esta región, dado que existe un vasto registro arqueológico de superficie –compuesto principalmente por artefactos líticos– y solo se cuenta con tipos morfológicos cronológicamente sensibles para el Holoceno Tardío. Aquí se presentan y evalúan 12 modelos para estimar las edades de los artefactos de obsidiana basados en la medición óptica de los anillos de hidratación. Específicamente estos modelos fueron desarrollados para las dos obsidianas más comunes en los contextos arqueológicos de la región, procedentes de las fuentes de Las Cargas y Laguna del Maule. Las edades estimadas son derivadas para cada fuente a partir de pares de medición del espesor de la corteza de hidratación-fechado radiocarbono, y calibradas con variables cuya influencia sobre la hidratación ha sido establecida experimentalmente. Las ecuaciones que presentamos son actualmente las que mejor predicen las edades conocidas de artefactos que han sido fechados independientemente por radiocarbono y, por lo tanto, pueden utilizarse con cautela para estimar la antigüedad de los artefactos de obsidiana procedentes de la región. Fil: Garvey, Raven. University of Michigan; Estados Unidos Fil: Carpenter, Tim. Archaeometrics; Estados Unidos Fil: Gil, Adolfo Fabian. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentina Fil: Neme, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentina Fil: Bettinger, Robert. University of California at Davis; Estados Unidos