Humans could be the only animals that are sensitive to fairness, suggests a new Royal Society Biology Letters study.

It's not that other animals are unfair. They just don't seem to care as much about fairness as we do, or so this and other research concludes.

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Ingrid Kaiser of the University of Heidelberg and colleagues focused their investigations on bonobos and chimpanzees. Chimps have long been regarded as the closest living relatives of humans.

For the study, the researchers presented their hairy participants with "the ultimatum theft game."

The below illustration and text from the paper illustrate how the game worked.

Instead of making offers, the chimp and bonobo subjects created the outcomes by stealing (or leaving) a portion of their partner’s share of grapes. Neither chimpanzees nor bonobos seemed to care whether food was stolen or not, or whether outcomes were fair or not, as long as they got something.

"Bonobos and chimpanzees in this study were equally insensitive to inequity," the researchers concluded.

They continued, "This finding is very different from what is found in humans, including children. While humans are strongly affected by concerns for fair allocations and fair intent, chimpanzees and bonobos do not appear to be."

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"Concern for fairness and other regarding preferences may thus be a derived trait in humans," they added. (A good explanation of what a derived trait is may be found on this page.) "These concerns are likely to have important implications for the evolution of human cooperation."

(Top Image: taliesin)