Bonobos say no to unfair trades, even if it costs rewards

Bonobos are known for gentle interactions, yet recent work suggests they might be less tolerant when rewards are split unequally. Researchers set out to see if these apes would walk away from deals that favored a partner and shortchanged them.

This insight emerges from the work of first author Kia Radovanović from Utrecht University. A team at the Max Planck Institute for Evolutionary Anthropology collaborated on these trials to gauge bonobos’ reactions to unequal treats.

Bonobos recognize unfair rewards and protest

Some experts use the phrase inequity aversion for patterns in animals that refuse to cooperate when they get a raw deal. Human studies have noted how people often protest if someone else is given better benefits for the same effort.

Bonobos share close ties with people on the evolutionary tree. Their social lives revolve around interactions where resources and tasks are commonly exchanged.

When tested in a token-exchange setting, they faced a scenario where one participant got a higher-value treat, while the other settled for a lesser option.

Why turn down free snacks?

“We found that bonobos more often refused to participate when faced with inequitable rewards,” said Radovanović. This outcome goes against the idea that they simply expect the same tasty morsel and quit if disappointed.

There were instances where an automated contraption handed out the treats. Bonobos avoided interacting if the gadget gave them a lower reward, yet spared a friend something tastier.

This trend did not appear to stem from dissatisfaction with the human caretaker but instead from the unequal handouts themselves.

How much unfairness can bonobos tolerate?

Cooperative behavior in this species is often viewed as a key characteristic. Some pairs seemed more tolerant of small imbalances, especially if they had strong social bonds.

The closer pairs of bonobos sometimes accepted the mismatch without walking away. These differences in how each ape responds hint that personal relationships might play a role in how big a difference in goodies they are willing to allow.

Bonobos, chimps, and unfair rewards

Unlike bonobos, chimpanzees in similar tests often show refusal patterns that seem tied more to the person handing out the food than to fairness itself.

When chimpanzees received lesser rewards, they reacted more strongly if the distributor was a human instead of a machine. That suggests they may be expressing frustration with the person, not necessarily protesting the unfairness of the trade.

Bonobos didn’t follow that same pattern. Their refusals were strongest when a machine was involved and their partner still got something better.

This detail sets them apart and raises the possibility that bonobos might have developed a clearer internal barometer for fairness, while chimpanzees may lean more toward social expectations or experimenter-based cues.

More tests to explore fairness in apes

Fair-minded behavior might develop from social structures that value harmony.

“This study provides new insights into how fairness may have evolved, but further research is needed,” said Daniel Haun, Director at the Max Planck Institute for Evolutionary Anthropology.

Researchers continue to plan follow-up tasks that offer group-based activities and broader test groups. They hope to see whether living conditions or group composition shape each individual’s perception of what is or is not an acceptable share.

Bonobos value rewards and fairness

People once believed that only humans show strong objections when rewards are lopsided. Bonobo evidence suggests some apes may notice these imbalances too.

This pattern could reinforce cooperation over time, because no one wants to keep playing with a partner who always gets the bigger prize.

These observations add a new perspective on how a sense of fair play might have taken shape in diverse primate lineages. Focusing on bonobos’ responses could clarify the complexities of social ties and resource division in living groups.

Can bonobos fix unfairness themselves?

Researchers propose testing different tasks where bonobos can actively equalize outcomes. Deeper analysis may also reveal if other apes respond similarly in varied settings.

Questions remain about how environment and familiarity influence the readiness to leave an unfair arrangement.

If bonobos keep showing that they can detect and reject unequal rewards, the idea of fairness in non-human species grows stronger. That could shift how we talk about morality and ethical conduct in the broader animal kingdom.

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

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