= Karl Sigmund
{c}
<Karl Sigmund> applies <mathematics> to the evolution of <cooperation>. His work in <evolutionary game theory> examines how strategies spread when their success depends on interactions with other individuals.https://www.leopoldina.org/en/members/member-list/detail/karl-sigmund[Leopoldina research profile; evolutionary game theory, replicator dynamics and cooperation]{ref}
With <Martin A. Nowak>, Sigmund developed a 1998 model of <indirect reciprocity>: an individual may help someone because that person's previous behaviour has established a favourable <reputation>, even if the same pair never meets again. The analysis combined mathematical conditions for stability with computer simulations of changing strategy frequencies.<Evolution of indirect reciprocity by image scoring by Martin A. Nowak and Karl Sigmund>[Nature 393, pp. 573–577; abstract and model]{ref}
For example, A helps B, C learns of the act, and C later helps A. The return to A passes through another individual instead of requiring repayment by B. The scientific question is which information and decision rules allow such behaviour to persist against alternatives that avoid the cost of helping. A reputation mechanism makes those rules explicit; it does not establish that every apparently generous action is explained by the same process.<Evolution of indirect reciprocity by image scoring by Martin A. Nowak and Karl Sigmund>[Model of reputation-based donor decisions without repeated pair encounters]{ref}
\Image[https://homepage.univie.ac.at/Karl.Sigmund/Sigmundpic.jpg]
{title=Karl Sigmund}
{description=Portrait linked from https://homepage.univie.ac.at/karl.sigmund/[Sigmund's University of Vienna homepage].}
Back to article page
