Xavier Vilà

Adaptive Artificial Agents Play a Finitely Repeated Discrete Principal-Agent Game

This paper approaches the analysis of a repeated Principal-Agent model introducing automata as a device for decision making. We use “modified” Genetic Algorithms methods to analyze the process of evolution in such a model. It is argued that the above modifications furnish the analysis with an interpretation that is more suitable to the study of social systems.

Social Interaction in Hunter-Gatherer Societies: Simulating the Consequences of Cooperation and Social Aggregation

This article describes the design and operation of an agent-based model that represents aspects of hunter-gatherer subsistence, technology, and cultural identity. The agents (representing families or households) in the model interact in a world that has a seasonally variable resource density. Agents must collect resources every step, either independently (by “gathering”) or with cooperation from neighboring agents (“hunting”). Several parameters affect cooperation: understanding these effects is one of the main focus of this article. Another focus is understanding the effects of cooperation in terms of cultural diversity/homogeneity. Some input parameters are historically and ethnographically calibrated, and the results are contrasted, with ongoing archaeological research of Patagonian hunter-gatherers (from 7000 BC or even earlier to 19th century). Specific research questions include how do processes of convergence and divergence occur between groups of hunter-gatherers over the long term? How could the autonomous local interactions of heterogeneous bounded rational agents generate this kind of regularity? What role outside influence plays on the formation of ethnic identities? Our aim is to integrate the state-of-the-art knowledge from different social sciences and technological developments into a fruitful approach to develop sociohistorical studies

Simulating Patagonian Territoriality in Prehistory: Space, Frontiers and Networks Among Hunter-Gatherers

In the last 40 years, the very idea of ethnicity has evolved from a static and essentialist classification of human groups according to their immutable “nature” to a relational frame of reference used by groups of people to consider themselves “similar” or to be explicitly differentiated by others. Nevertheless, the growing importance of variability analysis of mitochondrial DNA and other biological markers in modern prehistoric studies, with their emphasis on the identification of geographic patterns in genetic and phenotypic diversity of prehistoric populations is going in the opposite direction, as if the existence of genetic variability in the past would be comparable to what is inferred about cultural variation in the present. In this paper we have built a computer simulation of economic processes causing social aggregation, territoriality and ethnogenesis among Patagonian hunter-gatherers. We argue that cultural similarity and the constriction of groups to a restricted geographical area are not necessarily ethnic markers. Our model suggests that the more inter-generational knowledge transmission among socially aggregated individuals in the past, the greater the similarity in the social activity performed by agents in the present, and the same for their territoriality and the way frontiers and social networks were negotiated. Our computer simulation intends to answer the question “Why did human groups modify their traditional residence mobility and dispersal patterns?” In ancient Patagonia, at the extreme south of South America, from 12,000 BC until nineteenth century AD, this social transformation seems to coincide with slow changes in subsistence economy and technology. However, there are historical and archaeological sources that suggest this process was related with increased social complexity: wars and conflicts between different indigenous groups would have preceded this new scenario, even before European contact.

An unexpected course in the 6-exo radical cyclizations of trichloroacetamides on changing the N-substituent from benzyl to α-methylbenzyl

Abstract Radical cyclization of N-(α-methyl)benzyl substituted trichloroacetamides upon α,β-unsaturated nitriles has been studied. Tributyltin hydride treatment of trichloroacetamides 5a and 5b gives morphan derivatives (1 and 2), through a 6-exo-trig radical cyclization, and unexpectedly normorphans 6 and 7 as a result of a stereoespecific process in which the stereogenic benzylic carbon undergoes a configurational inversion.