Final Report Summary - COOPERATION (Evolutionary explanations for cooperation: microbes to humans) Cooperation plays a pivotal role at all levels of biological organization, from the genome to complex societies. We examined how cooperation can be maintained, examining both specific organisms, and the extent to which we can generalize across taxa. (1) Both experimental evolution studies on bacteria, and comparative studies across microorganisms and birds showed that genetic relatedness plays an analogous and key role in favouring cooperation. In asexual organisms, such as bacteria and algae, a high genetic relatedness results from clone-mates staying together rather than dispersing. A higher relatedness leads to both higher cooperation, and greater division of labour. In sexual organisms, a low level of promiscuity is also required, to ensure that siblings are closely related. A higher relatedness in birds leads to both a higher likelihood of cooperation, and a higher amount of cooperation. (2) Experimental studies on bacteria showed that the extent to which cooperation can be exploited by cheats depends upon a range of ecological and population parameters, such as population density, viscosity and the relative frequency of cheats in the population. (3) We found that the higher than expected levels of cooperation that have been observed in games with humans can be explained by ‘mistakes’ and do not require other-regarding preferences. (4) We showed theoretically how a number of ecological and environmental variables can interact to favour cooperation, between relatives, or between non-relatives. Population structure plays a key role in cooperation between relatives, and between greenbeard genes. The ability to reward cooperators or punish non-cooperators is predicted to play a key role in stabilizing cooperation between species.
