My primary research interest lies in the evolution of cooperation and the role of population structures. Cooperation is a central theme in evolutionary biology and forms the basis of communities of ’living’ systems ranging from replicating molecules to animal and human societies. The act of cooperation incurs some cost to the donor and produce a benefit to the recipient. Even though groups of cooperators are better off than groups of defectors the evolution of cooperative traits is far from obvious under Darwinian selection because cooperators are inherently prone to exploitation by defectors. Nonetheless, cooperation is abundant in nature. Although considerable progress has been made in theory and experiment, the understanding of how to offset the advantage of selfish cheaters is still far from complete. Since several years I am now working on different aspects of how to overcome this dilemma. In particular, this includes voluntary participation in social interactions, adding reward or punishment opportunities as well as effects of structured populations. More recently I became interested in modeling cancer biology as a fascinating application of evolutionary game theory in structured populations.
Complementing most of my recent research articles I have compiled interactive on-line tutorials on evolutionary game theory. This allows for a much better understanding of the systems dynamics through hands-on experiences and, besides, the fascinating and sometimes hypnotizing spatiotemporal patterns have quite some entertainment value.
Tutorial on frequency dependent selection in populations of varying size. The classic replicator dynamics assumes constant (infinite) population sizes and thus neglects the ecology of the population. Linking ecological dynamics and evolutionary games generates fascinating and rich dynamical behavior. Most importantly, however, this reveals a new mechanism for maintaining cooperation through negative feedback between population densities and the size of interaction groups (Hauert, C., Holmes, M. & Doebeli, M. (2006) Proc. R. Soc. Lond. B 273, 2565-2570).
Tutorial on cooperation in social dilemmas. Social dilemmas are characterized by a conflict of interest between the individuals and the group. The most prominent examples of social dilemmas are the prisoner's dilemma, the snowdrift game and public goods game. Based on the concept of synergistic or discounted accumulation of cooperative benefits we present a unifying framework to model cooperation in social dilemmas (Hauert, C., Michor, F., Nowak, M. & Doebeli, M. (2006) J. theor. Biol. 239, 195-202; Hauert, C. (2006) J. theor. Biol. 240, 627-636.
Tutorial on the fixation probability of mutants in structured populations where individuals are arranged on a graph. Each node represents an individual that is connected to other individuals. For a large class of graphs, the fixation probability does not depend on the details of the population structure and is identical to a homogenous population. All these graphs display the same characteristic balance between evolutionary selection and random drift. Nevertheless, the structure of the graph can have significant effects on the fixation probability ranging from complete suppression of selection to guaranteed fixation of advantageous mutants (Lieberman, E., Hauert, C. & Nowak, M., 2005 Nature 433 312-316).
Tutorial on the gradual evolution of distinct cooperative and defective behavioral patterns through evolutionary branching into separate trait groups characterized by high and low cooperative investments. This is based on a model that extends the classical Snowdrift game to continuously varying degrees of cooperation. Apart from evolutionary branching, this model exhibits rich dynamics that can be easily explored using this interactive tutorial (Doebeli, M., Hauert, C. & Killingback, T., 2004 Science 306 859-862).
Tutorial on the fate of cooperative behavior in two closely related evolutionary games: the Prisoner's Dilemma and the Snowdrift (Hawk-Dove) game. The population structure determines whether the evolution and maintenance of cooperation is promoted or hindered. In particular, this interactive tutorial illustrates that, in contrast to the Prisoner's Dilemma, spatial structure can be detrimental to cooperation in the Snowdrift game (Hauert, C. & Doebeli, M. 2004, Nature 428 643-646).
Tutorial on 2×2 games in populations with different structures. The most prominent game is certainly the Prisoner's Dilemma which has become the paradigm to discuss the emergence of cooperative behavior. If players are arranged on regular lattices, many of these games produce fascinating spatio-temporal patterns. This tutorial provides a hands-on experience of this dynamical world (Hauert, C. 2003, Int. J. Bifurcation and Chaos 12 1531-1548, Szabo, G. & Hauert, C. 2002, Phys. Rev. Lett. 89 118101).
Tutorial on public goods games with optional or voluntary participation. A virtual lab visualizes the time evolution of the frequencies of different strategies in the population. The dynamics is experienced by changing various parameters and verifying the consequences on the evolution of the system (Hauert, Ch., De Monte, S., Hofbauer J. & Sigmund, K. 2002, J. Theor. Biol. 218, 187-194).
Tutorial on public goods games with optional or voluntary participation in populations with rigid spatial structures. Another virtual lab illustrates the dynamics and offeres opportunities to explore a different world of spatio temporal patterns (Hauert, Ch., De Monte, S., Hofbauer J. & Sigmund, K. 2002, Science 296, 1129-1132).
Tutorial on effects of reward, punishment and reputation in social dilemmas simulated in well-mixed populations as well as on rigid spatial structures. Another virtual lab illustrates the dynamics and offeres opportunities to explore yet another world of spatio temporal patterns (Brandt, H., Hauert, Ch. & Sigmund, K. 2003, Proc. R. Soc. Lond. B 270, 1099-1104; Sigmund, K., Hauert, Ch. & Nowak, M. A. 2001, Proc. Natl. Acad. Sci. 98, 10757-10762).
As an introduction and preparation for the European Science Days in Steyr, Austria on The Evolution of Cooperation and Communication in July 2000, Karl Sigmund organized extensive internet experiments. The statistical evaluation and the results of the different games are discussed here.