title: Co-adaptation and the emergence of structure.
abstract: Co-adaptation (or co-evolution), the parallel feedback process by which agents continuously adapt to the changes induced by the adaptive actions of other agents, is a ubiquitous feature of complex adaptive systems, from eco-systems to economies. We wish to understand which general features of complex systems necessarily follow from the (meta)-dynamics of co-adaptation, and which features depend on the details of particular systems. To begin this project, we present a model of co-adaptation ("The Stigmergy Game") which is designed to be as a priori featureless as possible, in order to help isolate and understand the naked consequences of co-adaptation. In the model, heterogeneous, co-adapting agents, observe, interact with and change the state of an environment. Agents do not, ab initio, directly interact with each other. Agents adapt by choosing among a set of random "strategies," particular to each agent. Each strategy is a complete specification of an agent's actions and payoffs. A priori, all environmental states are equally likely and all strategies have payoffs that sum to zero, so without co-adaptation agents would on average have zero "wealth". Nevertheless, the dynamics of co-adaptation generates a structured environment in which only a subset of environmental states appear with high probability (niches) and in which agents accrue positive wealth. Furthermore, although there are no direct agent-agent interactions, there are induced non-trivial inter-agent interactions mediated by the environment. As a function of the population size and the number of possible environmental states, the system can be in one of three dynamical regions. Implications for a basic understanding of complex adaptive systems are discussed.
authors.affiliation: Department of Physics, University of Michigan, Ann Arbor, Michigan, United States of America ; Center for the Study of Complex Systems, University of Michigan, Ann Arbor, Michigan, United States of America.
authors.forename: Robert
authors.initials: R
authors.lastname: Savit
authors.forename: Maria
authors.initials: M
authors.lastname: Riolo
authors.forename: Rick
authors.initials: R
authors.lastname: Riolo
mesh_terms: D000223:Adaptation, Psychological; D003198:Computer Simulation; D004777:Environment; D030141:Feedback, Psychological; D005716:Game Theory; D006801:Humans; D008960:Models, Psychological
references.citation: Proc Biol Sci. 2011 Jul 22;278(1715):2198-206
references.pmid: 21147797
references.citation: Q Rev Biol. 2013 Mar;88(1):4-28
references.pmid: 23653966
references.citation: Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Oct;82(4 Pt 1):041919
references.pmid: 21230325
references.citation: Proc Biol Sci. 2011 Apr 7;278(1708):970-9
references.pmid: 21177681
references.citation: Science. 2012 Jan 27;335(6067):410-1
references.pmid: 22282796
references.citation: J Theor Biol. 2007 Apr 7;245(3):411-22
references.pmid: 17169377
references.citation: Phys Rev Lett. 2000 Jan 31;84(5):1058; author reply 1059
references.pmid: 11017442
references.citation: Biosystems. 2010 Feb;99(2):109-25
references.pmid: 19837129