“..in our paper we introduce a biologically interesting alternative to the Prisoner's Dilemma as described by the closely related Snowdrift game. In Snowdrift interactions cooperation remains prone to exploitation but cooperators also receive a share of the benefits.”

The paper breaks with the long-standing tradition that game theoretical studies on the evolution of cooperation are almost exclusively based on the "Prisoner's Dilemma." In game theory, the "Prisoner's Dilemma" is a type of non-zero-sum game in which two players can "cooperate" with or "defect" (i.e., betray) the other player. Based on a biologically appealing alternative, as described by the "Snowdrift game," (or "Hawk-Dove game"), it indicates that spatial structure may not be as universally beneficial for cooperation as previously thought and may even eliminate cooperation altogether.

It proposes the Snowdrift game as a complementing theoretical framework for modeling cooperation that is at least as relevant to biological applications as the traditional Prisoner's Dilemma.

The evolution of cooperation under Darwinian selection is an enduring conundrum in evolutionary biology. Because cooperation is costly and benefits others, it is prone to exploitation and should be selected against.

Over the last decades the Prisoner's Dilemma has been firmly established as the leading mathematical metaphor for studying cooperation using evolutionary game theory. One of the most important findings was that spatial structure with limited local interactions enables cooperators to survive by forming compact clusters such that they interact more often with other cooperators and thereby reduce exploitation by non-cooperating defectors.

Despite the vast theoretical literature on the Prisoner's Dilemma, it received surprisingly little support from experimental findings. In fact, to date, the Prisoner's Dilemma has been confirmed in detail only in a single system of RNA phages (Turner & Chao, Nature, 1999).

In our paper we introduce a biologically interesting alternative to the Prisoner's Dilemma as described by the closely related Snowdrift game. In Snowdrift interactions, cooperation remains prone to exploitation but cooperators also receive a share of the benefits. Because of these less stringent conditions, cooperators and defectors can co-exist under conditions where cooperators would go extinct in the Prisoner's Dilemma.

Quite surprisingly however, the relaxed conditions of the Snowdrift game tend to inhibit cooperation in spatially structured populations. Thus, our results caution against the common belief that spatial structure is necessarily beneficial for cooperation.

For interactive tutorials on the effects of space on cooperation visit the VirtualLabs.

The motivation for my research on cooperation and competition are that they form the basis of interacting communities ranging from replicating molecules to animal and human societies. Cooperation is ubiquitous in nature, yet the evolution of cooperation is a conundrum whereas exploitation is not. The identification of conditions and constraints that govern the evolution of cooperation represents a cornerstone for the biological understanding of the foundations of life.

The VirtualLabs, my growing collection of interactive tutorials that complement most of my more recent research articles, turned out to be very successful for a scientific site with an average of about 100 visitors per day. The VirtualLabs are being used in an increasing number of applied mathematics and biology courses at the undergraduate as well as graduate level.

The problem of cooperation will remain a hot and rewarding topic for quite some time. In the future, I would like to contribute to bridging the gap that has developed over the last decade between theoretical and experimental studies. This requires that theoretical studies focus on producing hypotheses that are, in principle, empirically testable. It also requires implementing biological relevance into theoretical models such as the promising interface and intriguing interplay between ecology and evolution.

The continuous formulation of the Snowdrift game (Doebeli, Hauert & Killingback, Science, 2004) proposes an evolutionary pathway for the origin of cooperators and defectors. In social endeavors, this spontaneous diversification means that evolution may not always lead to egalitarian outcomes with uniform cooperative contributions but instead favor situations where some individuals contribute maximally, while others keep their contributions at a minimum. We termed this situation the "Tragedy of the Commune" because (cultural) evolution may lead to highly asymmetric outcomes with large differences in cooperative contributions to communal enterprises. Based on the accepted notions of fairness such differences easily give rise to escalating conflicts.