En este trabajo se presentan los resultados de los análisis de isótopos estables (δ13Ccol, δ15Ncol, δ13Capa y δ18Oapa) realizados en huesos de camélidos de sitios de Puripica, Tulán y Salar de Punta Negra (Región de Antofagasta, Chile), dentro de una secuencia que abarca desde el Arcaico temprano hasta el Formativo temprano. Estos datos se cotejaron con datos osteométricos y genéticos de camélidos silvestres y domésticos con el objetivo de comprender el uso de los espacios de caza y pastoreo. Los resultados correspondientes a las muestras de los periodos Arcaico temprano y medio (10.000-5300 aP) obedecen a las características ambientales registradas durante dicho lapso temporal en el área. Para el Arcaico tardío (5300-4000 aP) y el Formativo temprano (3100-2400 aP) se observa una distribución de valores isotópicos relativamente similar. Sin embargo, debido a la alta variabilidad de tamaños dentro de los camélidos domésticos, no es posible definir el uso de ciertas áreas de pastura sobre otras. Al mismo tiempo, los valores isotópicos de carbono y nitrógeno de la fase Tarajne (3700-3200 aP) se muestran poco variables, patrón que se explica por el uso de áreas acotadas para la caza de animales silvestres y/o el pastoreo de animales domésticos.

Why do people sometimes hold unjustified beliefs and make harmful choices? Three hypotheses include (a) contemporary incentives in which some errors cost more than others, (b) cognitive biases evolved to manage ancestral incentives with variation in error costs and (c) social learning based on choice frequencies. With both modelling and a behavioural experiment, we examined all three mechanisms. The model and experiment support the conclusion that contemporary cost asymmetries affect choices by increasing the rate of cheap errors to reduce the rate of expensive errors. Our model shows that a cognitive bias can distort the evolution of beliefs and in turn behaviour. Unless the bias is strong, however, beliefs often evolve in the correct direction. This suggests limitations on how cognitive biases shape choices, which further indicates that detecting the behavioural consequences of biased cognition may sometimes be challenging. Our experiment used a prime intended to activate a bias called ‘hyperactive agency detection’, and the prime had no detectable effect on choices. Finally, both the model and experiment show that frequency-dependent social learning can generate choice dynamics in which some populations converge on widespread errors, but this outcome hinges on the other two mechanisms being neutral with respect to choice.

Mathematical models and simulations demonstrate the power of majority rules, i.e. following an opinion shared by a majority of group members. Majority opinion should be followed more when (a) the relative and absolute size of the majority grow, the members of the majority are (b) competent, and (c) benevolent, (d) the majority opinion conflicts less with our prior beliefs and (e) the members of the majority formed their opinions independently. We review the experimental literature bearing on these points. The few experiments bearing on (b) and (c) suggest that both factors are adequately taken into account. Many experiments show that (d) is also followed, with participants usually putting too much weight on their own opinion relative to that of the majority. Regarding factors (a) and (e), in contrast, the evidence is mixed: participants sometimes take into account optimally the absolute and relative size of the majority, as well as the presence of informational dependencies. In other circumstances, these factors are ignored. We suggest that an evolutionary framework can help make sense of these conflicting results by distinguishing between evolutionarily valid cues – that are readily taken into account – and non-evolutionarily valid cues – that are ignored by default.

This paper analyzes whether herding and skillful managers may coexist. When herding appears, managers tend to present poor timing abilities; however, a weak herding level (a result commonly found in pension funds) may evidence a mixed scenario, where some managers develop skills, and others follow the herd. Additionally, when informational cascades emerge, some managers may act as leaders, anticipating others’ movements. Nonetheless, this anticipatory skill does not mean that leaders also anticipate market movements and present timing skills. Our results show herding and inter-temporal herding in a sample of Spanish pension funds, though the imitation behavior is not strong. We also find evidence of a mixed scenario, in which some non-herding managers present timing skills, while herding funds are not able to develop these abilities. Finally, we find successful timing for certain leaders, showing that the anticipation of others’ movements does not show real timing abilities.

The author notes that livestock herding in the Kalahari Desert would require water during the dry season. By mapping and dating artificially dug or enlarged waterholes, he shows when and where such herding would have been possible. Dating is by radiocarbon, artefact scatters and cartography. Comparison with climatic, documentary and oral evidence shows that the use of the artificial wells correlates with what is known so far about the movement of peoples over the last two millennia. This inspires confidence in the connection between the wells and herding and in the survey methods.

We consider a model in which foreign and domestic traders buy the assets of both of two countries. Speculators in both countries use chartist or fundamentalist rules for forecasting the exchange rate. Demand for the assets of each country is determined by these forecasts. Perceptions of the fundamentals in each country are not necessarily the same. Rules are used with a certain probability depending on an agent's previous experience with them. The demands of the fundamentalist and chartist agents in the two countries determine the temporary equilibrium exchange rate at each point in time. This is unique under certain assumptions. With traders of both nationalities there is no need, as in other models, for an exogenous supply of foreign exchange. The model produces realistic features of the equilibrium exchange rate series. Periods in which the exchange rate tracks the fundamentals of one of the countries alternate with others in which bubbles appear.

This issue contributes to the discussion of the relation between individual and aggregate behavior. The basic feature of all the models presented is that they allow for direct interaction between the individuals. This, it is shown, leads to a number of interesting phenomena that are difficult to account for in standard models. The basic message is that the inclusion of heterogeneous interacting agents allows us to escape from the pitfalls associated with the reduction to a representative individual and furthermore to show that aggregates will, in general, have behavior that is different from that of the component individuals. Lastly, complex aggregate behavior is not necessarily the result of complicated individual reasoning, it can emerge from very simple rule following by individuals.

This paper studies the relationship between rational herding and cross correlations in security returns. It demonstrates analytically and numerically that herding, as a temporary, fragile convergence of investment behavior, can endogenously induce asset dependency. Furthermore, there exists a self-reinforcing process, in which market extreme events amplify the herd effect, which further exacerbates asset dependency. Considering the Taiwan and U.K. equity markets, we find that the simulated markets in the presence of herding have results closer to the real patterns of asset dependency than a static model with isolated, noninteracting individuals. Our findings cast doubts on the current view that transparent financial regulation is always desirable. Moreover, this paper finds statistical evidence of asymmetric correlation patterns in both the top 50 stocks in the U.K. and Taiwan equity markets. This suggests that portfolio diversification as a means of managing portfolio risk is unlikely to be effective in periods of extreme losses in these markets.