Untangling the contribution of active and passive group augmentation benefits to the multilevel selection of altruism using a video game

The group augmentation hypothesis states that individuals gain benefits by increasing group size and is rarely studied because it often overlaps with other evolutionary mechanisms like reciprocity. When rescuing a fellow prey from death, the mere presence of that member in the group can yield different benefits that can be passive like risk dilution or active like delayed reciprocity. We were able to separate the effects of passive and active group augmentation benefits by experimentally manipulating the behaviour of prey (altruist vs. non-altruist) in a video game where the costs and benefits of altruism were easily measured. The game pits four players-prey that must acquire resources to survive, while avoiding getting captured by a fifth player-predator. We instructed half of the prey players to avoid rescuing other prey, and the other half to rescue when possible. Our data showed that increasing the frequency of altruistic prey in a group increased survival of all group members. Maintaining group size yielded passive benefits like improving resource acquisition and facilitating future rescues. These passive benefits had a higher impact on survival than the active benefits (e.g., being rescued in return through reciprocity). Thus, we were able to support the importance of passive benefits from anti-predator altruistic behaviour using a biologically relevant online video game.