Chimpanzees' Response to (Un)Fairness

Brosnan, S. F. & de Waal, F. B. M. (2014). Evolution of responses to (un)fairness. Science. doi: 10.1126/science.1251776


Recent Interviews with Frans de Waal


Recent Essays by Frans de Waal


Chimpanzees' Music Preference

Mingle, ME, Eppley, TM, Campbell, MW, Hall, K, Horner, V, & de Waal, FBM. (2014). Chimpanzees prefer african and indian music over silence. Journal of Experimental Psychology: Animal Learning and Cognition. doi: 10.1037/xan0000032

Chimps Like Listening to Music with a Different Beat

By American Psychological Association.


Elephants Reassurance

Plotnik, J. M. & de Waal, F. B. M. (2014). Asian elephants (Elephas maximus) reassure others in distress. PeerJ, 2, e278. doi:10.7717/peerj.278


Bonobo Consolation

Clay, Z. & de Waal, F. B. M. (2013a). Bonobos respond to distress in others: Consolation across the age spectrum. PLoS One, 8, e55206. doi:10.1371/journal.pone.0055206
Clay, Z. & de Waal, F. B. M. (2013b). Development of socio-emotional competence in bonobos. Proceedings of the National Academy of Sciences. doi:10.1073/pnas.1316449110

Apes comfort each other ‘like humans’

By Victoria Gill, BBC Nature.

Young bonobos offer comforting hugs and sex

By Ella Davies, BBC Nature.


Chimpanzee Fairness Study

Proctor, D., Williamson, R. A., de Waal, F. B. M., & Brosnan, S. F. (2013). Chimpanzees play the ultimatum game. Proceedings of the National Academy of Sciences. Advance online publication. doi:10.1073/pnas.1220806110

Jan 14, 2013. We have reached quite a milestone today with the publication of our study on primate fairness. I will post a few press articles. There are many.

Most of you know our monkey study showing the vigorous protest by the monkey who gets cucumber while another gets grapes. This study is 10 years old, however. Now we have done the impossible by having chimps play the Ultimatum Game. This game is the absolute gold standard for fairness in humans, and has been played all over the world with humans in different cultures. One individual needs to split a money amount with another and if the other accepts the proposed split both will get their share. Humans make fair offers, probably because they are afraid that the other may otherwise reject. In that case they will both end up empty-handed.

It is not easy to get chimps to make an offer to each other and the other to express acceptance. This is much easier done with linguistic creatures. Previous attempts used such complex apparatuses that the chimps were quite confused, even accepting zero offers, which no sane primate, human or nonhuman, should ever do.

Dr. Darby Proctor, a student of Sarah Brosnan and now a postdoc with us, worked for years diligently on getting chimps to understand a much simpler procedure. Once they did, she could play the Ultimatum game with them. The choices the chimps made were entirely their own, they were not trained or rewarded by us for what they chose. It was up to them. We tested young children in exactly the same way. The children and chimps reacted in the same way, making strikingly fair offers.

Our conclusion is that the human sense of fairness blends with that of the chimpanzee. The differences, if any, are rather unclear. An interesting development given how much ink philosophers and economists have spilt over where this sense comes from, concluding that it must rest on a “concept” of justice … I am not so sure about this, I always thinking that things are simpler than people think.

Appended is a video of Dr. Proctor's experiment.

Technical note: The German team that conducted previous unsuccessful Ultimatum Games with apes is distinctly unhappy with our results and has expressed their skepticism in the media. It all depends on what the Responder does, they say. Human fairness preferences, however, are measured in the Proposer, not in the Responder, and the human version is usually played only one time so there is not much opportunity for rejections. Rejections are not the main measure, therefore. Our chimps (as well as the children) clearly expressed dissatisfaction with selfish offers, which a) indicates that they understood how things worked, and b) were trying to forestall unfair offers. That's exactly the point of the Ultimatum Game. Manfred Milinksi wrote a commentary in PNAS stressing the significance of these additional observations.


Fairness in Chimpanzees

Academic Minute, Inside Higher Ed.

Chimps can play fair, too

By Nolan Feeney,

For more information also see Dr. Proctor's recent blog post.