 In contrast, another fascinating area of research, evolutionary game theory (see entry on  evolutionary game theory),  investigates how features like altruism, social norms, moral behavior and cooperation could actually have evolved. This area combines both normative and descriptive work (Axelrod 1984; Bowles and Gintis 2011; Sigmund 2010). As a particular social software contribution to this area, Gärdenfors (2012) characterized how much cognition and communication are required for several kinds of cooperation, from simple flocking behavior, through reciprocal altruism (“I’ll scratch your back if you scratch mine”), up to fully fledged teamwork.