Another kind of dilemma

In the heart of the Arctic Ocean, a pair of stickleback fish is on the hunt for prey. A fierce-looking rainbow trout quickly approaches and the fish are suddenly nervous. With a predator nearby, each fish is now faced with a life or death situation. Should they act together and maximise their chances of survival? Or, should each act to save itself, and leave the other behind?

This strategic interaction contains many elements of the classic Prisoner’s Dilemma game. When faced with a formidable predator, each animal prefers to act independently to maximise survival, even though acting together presents a better chance of staying alive in the long term.

Interestingly, stickleback fish display cooperative behaviour in the face of predators. When one fish makes a risky dart to safety, the other follows. If one stays behind, so does the other.

But why do animals display cooperative behaviour in Prisoner Dilemma situations? The animal kingdom has long favoured survival of the fittest. In the quest for survival, stickleback fish support one another due to the concept of group selection – the idea that survival is enhanced by working together.

Vervet monkeys also have an interesting way of dealing with predators. When in danger, vervet monkeys revert to a unique alarm call, warning fellow kin that danger is imminent. However, doing so attracts attention, decreasing the likelihood of survival. So why do vervet monkeys put their own lives on the line for their peers?

One answer is kin selection, which is the notion that aiding peers helps the individual. Over time, a vervet monkey is likely to have numerous encounters with predators. As they play this Prisoner’s Dilemma game repeatedly over time, vervet monkeys know they are more likely to survive by calling their kin, so they act cooperatively to avert danger in the long run.

Another example of cooperation can be found in the behaviour of vampire bats. They ‘solve’ the Prisoner’s Dilemma game in yet another way. Vampire bats feed off the blood of domestic livestock such as cattle and horses. But they are not always successful in obtaining food. Those that fail to do so will plead for food from their kin, licking them under their wing and on the lips. The successful vampire bat then faces a decision: whether to share its meal with the hungry neighbour or not. The figure below illustrates the matrix to this interaction:


Each bat again has a dominant strategy of not sharing food, as sharing diminishes their food stock. As a result, the stable outcome in this encounter is for each vampire bat to not share its meal. Yet in many instances, this result is not reached. Again, cooperative behaviour dominates. Researchers believe vampire bats share food because of reciprocity. Although sharing food today reduces their fitness, vampire bats still cooperate with each other in expectation of altruism in the future.

Upon closer examination, animal behaviour is by no means primitive or irrational. In fact, animals can often ‘solve’ Prisoner Dilemma games more optimally than humans. While we, as humans, often let self-interest prevent cooperation even when it leads to optimal outcomes, many species of animals seem to have no such problem.

But, then again, perhaps this phenomenon only occurs because humans and animals are ultimately faced with a different set of decisions. Animals are able to effectively work together because their choices involve life or death situations. For humans, on the other hand, we often apply the Prisoner Dilemma game to self-interested firms, for example, that behave strategically to maximise profits.

But in the face of an apocalypse, how would we react? If the walls of civilisation as we know it were to come crumbling down, would we humans be able to display cooperative behaviour like animals do, to survive, rebuild, and once again prosper?