printed by The question how the human brain works can be approached from different angles. Scientists from disciplines like biology, neuroscience, psychology and philosophy try to solve this problem. The human brain is like all nervous systems an information-processing system. Therefore the comparison of information-processing models from computer science with results from empirical neuroscience, describing the evolution of neural networks as well as complex social behavior can be very useful for the understanding of this complex problem. The high degree of complexity of social behavior on the neural level is the reason why science was not yet able to find satisfying answers to most of the questions concerning the meaning of neurophysiological correlates found in the human brain. This complexity evolved over millions of years to enable humans to interact in a purposeful way with a constantly changing and noisy environment. The functions of the human brain are physical manifestation of actual behaviors performed by an individual or a group of individuals. These behaviors evolved due to challenging situations in the environment and the drive to survive and reproduce. Therefore each species has its own behavior patterns while interacting with the environment. Social behaviors as well as individual behaviors can be seen as the connection between brain activity and environmental challenges. One possible approach to the question “How to build a brain?” is to create a model which will help us to understand the complex social interactions between individuals, how individuals plan and how decision making influences the action selection process. The understanding of social behavior will help us to understand the complexity involved in all higher cognitive brain functions. It is not only important to understand how the human brain works, but also why it works. INTRODUCTION REFERENCES Figure1: Hemelrijk implemented grouping rules and rules for interactions in her model. Depending on their internal state (in the model represented by the dominance value) the agents will engage in dominance interactions. This will change the dominance value of the agents, depending on the result. The agent which looses the interaction will then flee from its opponent. To maintain the group structure she implemented a search procedure during which each agent, which is not involved in a fight searches for its nearest partner in the group. Real primate societies: Tolerance is one of the most basic forms of conflict resolution in social species (de Waal & Luttrell, 1989). It is for example expressed when a dominant animal allows a subordinate to take advantage of a resource in its presence. For species with low levels of tolerance most conflicts are unidirectional: subordinate animals make no effort to retaliate for an attack by a dominant, and would almost never attack a dominant themselves. Conflicts tend to be infrequent, but when they occur, they are highly intensive (e.g. biting) and reconciliation behavior afterwards is rare. In species with high levels of tolerance conflicts are more frequent and bidirectional, and the majority of these interactions is being met with protests or counter-attacks, but the intensity of aggression is low. - Greeno J.G. (1994). Gibson's affordances — Psychological Review 101(2), p de Waal, F. B. M. and Luttrell, L. (1989). Toward a comparative socioecology of the genus macaca: Different dominance styles in rhesus and stumptailed macaques. Am. J. of Primatology, 19:83– Hemelrijk, C. K. (1999). An individual-oriented model on the emergence of despotic and egalitarian societies. Proc. of the R..Soc.: Biol. Sc., 266: Hemelrijk C.K. (2002). Self-organization and natural selection in the evolution of complex despotic societies. — Biol. Bull. 202, p Hemelrijk C.K. (2002). Despotic societies, sexual attraction and the emergence of male ”tolerance”: an agent-based model — Behaviour 139, p Thierry, B., Singh, M., and Kaumanns, W., editors (2004). Macaque Societies: A Model for the Study of Social Organization.Cambridge University Press. de Waal, F.B.M. (1989). WHY AN EVOLUTIONARY PERSPECTIVE? Before creating a complex artificial system to simulate functions in natural processes it is important to understand these functions and their meanings in nature. This will help to avoid redundancy and enable us to create ecological valid, working systems. Especially since the goal is not to rebuild the physiology of the human brain but to understand and simulate its functions. The evolutionary perspective can help to achieve this, since it is a top down approach. One of the main problems in AI is that agents have to recognize the circumstances under which certain rules, on which these agents are based, have to be applied to solve a task. These agent-situation interaction patterns are called affordances in ecological psychology (Greeno 1994). Animals and humans are very good in recognizing such affordances, which is why they are flexible and efficient in their reactions. COMPARING NATURAL PROCESSES WITH THE MODEL Social interactions are the central element for the understanding of the evolutionary mechanism of higher cognitive functions. An ecological valid model which can help us to understand the human brain will therefore have to include functions to simulate social behavior found in real animal societies. Thierry et al. (2004) propose that the genus macaca is a particularly good model for studying primate social organization. There are twenty-one known macaque species. From a genetic perspective they are very similar, but they differ widely in their social interaction. Their styles of social interaction range from egalitarian to despotic and their repertoire of social behaviors differs according to that. Model primate societies: As an example for current models of primate social interactions we choose Hemelrijk`s DomWorld (Hemelrijk 1999, 2002), because it is the most widely- published agent based models in biology. Hemelrijk was able to simulate, with different additions to her basic model (Figure1), phenomena like female dominance and sexual attraction (Hemelrijk 2002). Her model is supported by results of her own field research. But it is too simple (it does not include any higher cognitive functions) to be useful to help to answer the question of “how to build a brain”. HEMELRIJK‘S DOMWORLD ALTERNATIVE MODEL Our model focuses on different functions of social behavior. We integrate the most basic variables of motivation. Social interactions are based not only on the mechanisms underlying tolerance but depend on a variety of different motivations. This system of different motivations is hierarchical and includes specific processing units to act in a situation with the ability to stay flexible to choose other goals, in case the situation changes. The mechanism operates on a top down level. A full expression of all included processes would be very complex, therefore we only picked the eating behavior to illustrate the sequence of actions. CHECK INTERNAL STATE LEVEL OF DESIRE THRESHOLD LEVEL OF RISK - SEARCH FOR FOOD MOVE TO FOOD EAT FOOD CHECK INTERNAL STATE LEVEL OF DESIRE MODIFICATIONS OF WEIGHTS + How to build a brain – The social aspect in evolution Hagen Lehmann† & Tino Schmidt‡ †University of Bath, Artificial models of natural Intelligence ‡Technische Universitaet Dresden, Institut fuer Allgemeine Psychologie TECHNISCHE UNIVERSITÄT DRESDEN