Synergy, partner choice and frequency dependence: their integration into inclusive fitness theory and their interpretation in terms of direct and indirect fitness effects

The aims of our Target Review (Lehmann & Keller, 2006) were to develop a simple model allowing us to delineate the conditions necessary for cooperation and altruism to evolve and argue that the models proposed so far can all be classified into four general categories depending on the selective forces at work. These are direct benefits to the Focal Individual (FI) performing a cooperative act, repeated interactions with direct or indirect information on the behaviour of the partner in previous moves, preferential interactions between related individuals and/ or a linkage disequilibrium between genes coding for altruism and phenotypic traits that lead to assortment of individuals bearing altruistic genes (i.e. greenbeard effect). We were extremely pleased to see that authors of 14 of the 15 Commentaries found our framework useful and generally endorsed our views. Doebeli & Fletcher (2006) were the only authors who fundamentally disagreed with our classification. However, their criticisms mostly stem from a misunderstanding of our model and kin selection theory. Several Commentaries raised similar general issues, in particular about the assumptions of our model and/or alleged limitations of Hamilton’s rule. We therefore address these comments in the first four general sections. Following these, we address the criticisms raised by Fletcher and Doebeli (2006). Finally, in the two last sections, we discuss all the other specific comments raised in the Commentaries, and finish with a short conclusion.