Cooperative Brains: Psychological Constraints on the Evolution of Altruism

Imagine an individual called “hunter” that expends a good deal of energy to capture a gazelle. As the hunter is consuming his small prey, a second individual called “recipient” approaches and begins feeding peacefully alongside the hunter. A few weeks later the roles reverse, such that the previous recipient has now captured a gazelle, and the previous hunter is taking advantage of the recipient’s hard work. Could the hunter and recipient be Maasai warriors? Is it equally likely that they are common chimpanzees, African lions, or Nile crocodiles? All of these species hunt gazelle and live in groups, so why would this scenario apply to some species more appropriately than to others? The answer lies in the costs and benefits associated with sharing food with non-kin. Assuming that one individual can consume the entire gazelle, sharing food with the recipient constitutes an altruistic act—the hunter accepts a fitness cost (reduction in food intake) while increasing the fitness of another (increasing the intake of the recipient).