People will reject an offer of water, even when they are severely thirsty, if they think the offer is unfair, according to a new study by researchers at the Wellcome Trust Centre for Neuroimaging at UCL. The findings have important implications for understanding how we make decisions that need to balance fairness and self-interest.
In studies that require people to share out money, it has been known for some time that the person receiving an offer will tend to reject it if they think it unfair, preferring to let both parties walk away with nothing rather than accept a low offer in the knowledge that the other person is taking home more.
In contrast, our closest relatives, chimpanzees — when bargaining for food — will almost always accept an offer regardless of any subjective idea of ‘fairness’.
This study was designed to find out whether humans would similarly accept unfair offers if they were bargaining for a basic physiological need, such as food, water or sex.
The team recruited 21 healthy participants and made 11 of them thirsty by drip-feeding them a salty solution, while the others received an isotonic solution that had a much smaller effect on their level of thirst. The participants reported their own perceptions of how thirsty they were using a simple rating scale, and to obtain an objective measure of each individual’s need for water, the team measured the salt concentration in their blood.
The participants then individually took part in an ultimatum game. They were told that two of them had been randomly selected to play a game to decide the split of a 500 ml bottle of water that could be consumed immediately. One of them would play the part of ‘Proposer’ and decide how the bottle should be split. The other would be a ‘Responder’ who could either accept the split and so drink the offered water, or reject the split so that both parties would get nothing. The participants knew that they would have to wait a full hour after the end of the game before they would have another chance to drink anything.