Short abstract, isn't it? P.A.C.S. numbers 05.20, 02.50, 87.10 1 Introduction Large Numbers "...the optimal tour displayed (see Figure 6) is the possible unique tour having one arc fixed from among 10 655 tours that are possible among 318 points and have one arc fixed. Assuming that one could possibly enumerate 10 9 tours per second on a computer it would thus take roughly 10 639 years of computing to establish the optimality of this tour by exhaustive enumeration." This quote shows the real difficulty of a combinatorial optimization problem. The huge number of configurations is the primary difficulty when dealing with one of these problems. The quote belongs to M.W Padberg and M. Grotschel, Chap. 9., "Polyhedral computations", from the book The Traveling Salesman Problem: A Guided tour of Combinatorial Optimization [124]. It is interesting to compare the number of configurations of real-world problems in combinatorial optimization with those large numbers arising in Cosmol...

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Introduction As language users humans possess a culturally transmitted system of unparalleled complexity in the natural world. Linguistics has revealed over the past 40 years the degree to which the syntactic structure of language in particular is strikingly complex. Furthermore, as Pinker and Bloom point out in their agenda-setting paper Natural Language and Natural Selection \grammar is a complex mechanism tailored to the transmission of propositional structures through a serial interface" (Pinker and Bloom, 1990, 707). These sorts of observations, along with inuential arguments from linguistics and psychology about the innateness of language (see, e.g. Chomsky, 1986; Pinker, 1994), have led many authors to the conclusion that an explanation for the origin of syntax must invoke neo-Darwinian natural selection. \Evolutionary theory oers clear criteria for when a trait should be attributed to natural selection: complex design for some function, and the absence of alternative proc

This paper lists fourteen open problems in artificial life, each of which is a grand challenge requiring a major advance on a fundamental issue for its solution. Each problem is briefly explained and, where deemed helpful, some promising paths to its solution are indicated. Introduction At the dawn of the last century, Hilbert proposed a set of open mathematical problems. They proved to be an extraordinarily effective guideline for mathematical research in the following century. Based on a substantial body of existing mathematical theory, the challenges were both precisely formulated and positioned so that a significant body of missing theory needed to be developed to achieve their solution, thereby enriching mathematics as a whole. In contrast with mathematics, artificial life is quite young and essentially interdisciplinary. The phrase artificial life was coined by C. Langton [13], who envisaged an investigation of life as it is in the context of life as it could be. Although artifi...

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A growing body of work demonstrates that syntactic structure can evolve in populations of genetically identical agents. Traditional explanations for the emergence of syntactic structure employ an argument based on genetic evolution: syntactic structure is specified by an innate Language Acquisition Device (LAD). Knowledge of language is complex, yet the data available to the language learner is sparse. This incongruous situation, termed the "poverty of the stimulus", is accounted for by placing much of the specification of language in the LAD. The assumption is that the characteristic structure of language is somehow coded genetically. The effect of language evolution on the cultural substrate, in the absence of genetic change, is not addressed by this explanation. We show that the poverty of the stimulus introduces a pressure for compositional language structure when we consider language evolution resulting from iterated observational learning. We use a mathematical model to map the space of parameters that result in compositional syntax. Our hypothesis is that compositional syntax cannot be explained by understanding the LAD alone: compositionality is an emergent property of the dynamics resulting from sparse language exposure.

Most contracts, whether between voters and politicians or between house owners and contractors, are incomplete. “More law,” it typically is assumed, increases the likelihood of contract performance by increasing the probability of enforcement and/or the cost of breach. This paper studies a contractual relationship where the first mover has to decide whether she wants to enter a contract without knowing whether the second mover will perform. We analyze how contract enforceability affects individual performance for exogenous preferences. Then we apply a dynamic model of preference adaptation and find that economic incentives have a non–monotonic impact on behavior. Individuals perform a contract when enforcement is strong or weak but not with medium enforcement probabilities: Trustworthiness is “crowded in” with weak and “crowded out” with medium enforcement. In a laboratory experiment we test our model’s implications and find support for the crowding prediction. Our finding is in line with the recent work on the role of contract enforcement and trust in formerly Communist countries.

This paper reports a set of computer simulations that demonstrate a form of adaptation that we believe to be characteristic of human intelligence. One of the central problems faced by biological and artificial systems is the development and maintenance of coordination between structure inside the system and structure outside the system. That is, the production of useful behavior requires internal structures that respond in appropriate ways to structure in the environment. The processes that give rise to this coordination are generally considered adaptive. Biological evolution, individual learning, and cultural evolution can all be viewed as ways to discover and save solutions to frequently encountered problems—they are processes that generate coordination between internal and external structure.

A computer simulation modeled the change of attitudes in a population resulting from the interac-tive, reciprocal, and reeursive operation of Latan~'s (198 I) theory of social impact, which specifies principles underlying how individuals are affected by their social environment. Surprisingly, several macrolevel phenomena emerged from the simple operation of this microlevei theory, including an incomplete polarization of opinions reaching a stable equilibrium, with coherent minority sub-groups managing to exist near the margins of the whole population. Computer simulations, neglected in group dynamics for 20 years, may, as in modern physics, help determine the extent to which group-level phenomena result from individual-level processes. Writing about social phenomena, social scientists have pro-duced empirical generalizations and theoretical analyses of so-cial processes representing differing levels of social reality. Some analyses concern the cognitions, feelings, and behavior of individuals; others deal with small, medium, or large groups, collectivities, and organizations; still others involve such large-scale human aggregates and systems as nations, societies, or cul-

This paper focuses on the phenomena of evolution whose appearance is notable because no explicit mutation, recombination or artificial selection operators are introduced. We call the system self-evolving because every variation is performed by the objects themselves in their machine form. Keywords: artificial chemistry, autocatalytic reaction system, molecular computing, prebiotic evolution, self-organization, self-programming 1