Why do most of us work together for the common good, even when it might personally benefit us more to cheat? Is it because we fear we would be punished for not following the rules? Because we have been taught to treat others as we would want to be treated?

Because cooperation is vital for survival in a variety of contexts, it may be that fair play is an evolutionary adaptive behavior, scientists say. Of course, the flip side is that when an individual does behave selfishly, others often use some form of negative reinforcement to dissuade such behavior in the future.

It appears animals do the same. First, though, an animal must recognize unfair situations. To find out if primates can do so, Dr. Sarah F. Brosnan of Georgia State University and her colleagues set up a series of experiments in which pairs of primates were trained to perform the same task, but one received a much tastier reward. Brosnan discovered that they do realize (and respond negatively) when another primate receives a "better" reward for completing the same task. Even when they get the same reward they did before (in the control situation) that they were happy with, the animals will not be satisfied "if a partner gets a better deal," Brosnan and Dr. Frans B. M. de Waal say in their article. Primates "clearly have to be able to assess quantities or qualities and compare them, so there is a baseline level of cognition which is required," said Brosnan.

Sometimes, certain primates will refuse food rewards that they deem insufficient. Like petulant children, primates have been known to toss the reward from the test chamber. "When I began the research, I never expected to see individuals refusing food rewards," Brosnan said.

So, what about the other animal, the one that who received more food? Even though they were better rewarded, these chimpanzees refused to participate more often than when the food was distributed more fairly. Is this due to a sense of justice? Or just a desire to avoid retaliation (in other words, punishment) from their partner chimp after the experimenter leaves?

In a similar study using dogs as subjects, when two dogs performed the same task and one dog received a reward when the other didn't, the "slighted" dog recognized the unfair treatment and began to refuse to obey the experimenter. However, unlike the primates, the dogs did not seem to notice when the other dog received a larger or better reward, as long as they both received something.

Although we might expect it of our primate relatives, and even dogs who spend so much time with humans, it seems humble fish also recognize when they're being cheated. Cleaner fish, as the name implies, remove dead skin, parasites, and other bits of junk on larger "client" fish. However, the fish tend to prefer the healthy scales and mucus to the dead cells, so they will sometimes "cheat" and bite the body itself of the client fish. Naturally, these bites often cause the client to swim away, thus depriving the cleaner fish (and their cleaning partners) of a meal.

Image courtesy of João Paulo Krajewski.
Dr. Nichola Raihani, a Postdoctoral Research Fellow at the Institute of Zoology, Zoological Society of London and her colleagues have done research that indicates male cleaner fish punish more harshly females who cheat with higher-value clients.

Raihani and her colleagues tested the fish in the laboratory to simulate conditions in the ocean. To represent client fish, they prepared a plate of food with both fish flakes (which cleaner fish like okay) and prawns (which the fish love). A low-value plate had four fish flakes while high-value ones had eight. The experimenters put a plate of food in front of each pair of cleaner fish (one male, one female). They were allowed to eat as many of the fish flakes as they liked, but as soon as one of them ate a prawn, the plate of food was removed (to simulate the client fish swimming away). The researchers then measured the level of punishment (aggressive chasing) that the male doled out to his partner.

It turns out that males recognize the difference between the high-value the low-value clients and punish the females more when a higher-value client swims away, an ability that demonstrates some level of intelligence on its own. Furthermore, "Females are able to associate their own cheating behavior with a negative response from the male," said Raihani, and are less likely to eat the prawn the next time. "Cleaner fish are a great study system because they learn things so quickly in the lab. That never fails to surprise me," Raihani said. "Cleaners can be taught to eat the less-preferred food (by removing the 'client' when the cleaner eats prawn) in just 6 trials - quite amazing!"

Scientists often look at animal behavior and draw parallels to human society. For example, how do these examples of animal punishment relate to our own justice system? How does the economics of treat rewards relate to our own, obviously much more complicated, economic system? "Lots of the work we do on cleaner fish is directly relevant to human behavior. Cleaners and clients interact in a biological 'market' - just as humans interact with one another in economic markets. What we are trying to understand is how good service quality is maintained in a biological market, even when the service providers (in this case, the cleaner fish) are tempted to cheat. Human service providers are also often tempted to cheat. For example sellers on eBay, would - all else being equal - profit most from taking buyers' money but then failing to deliver the goods. The thing that maintains cooperation in this sort of trading environment is the threat of punishment (e.g. prosecution) and the potential for disgruntled buyers to leave negative feedback about cheating sellers. Sellers experience costs from a damaged reputation because they are less likely to be chosen for interactions by other prospective buyers in the future."

Ultimately, scientists say, these behaviors promote cooperation. Brosnan says that noticing and reacting against inequities seems to promote cooperation among primates, especially amongst those who aren't related to each other, and who thus might otherwise be disinclined to cooperate. In fish, cooperation is ensured through punishment. "This is the first evidence," Raihani and her colleagues said in their article, "for flexible adjustment of a punishment and corresponding responses of targets in a non-human species."

This post is part of the series Animal Acumen, an exploration of animal cognition. Visit other posts in this series.

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