In a new study, thirsty people rejected an offer for a drink of water if they knew one of their fellow research subjects would get a much bigger glass, suggesting people sometimes overlook their own best interests to take a stand against unfairness.

Researchers at the Wellcome Trust Centre for Neuroimaging at University College London recruited 21 healthy participants for the small study and made 11 of them very thirsty by drip-feeding them a salty solution. The subjects were then told they would be paired with another participant and one of them, the proposer, would get to decide how to split a bottle of water with the other, the responder. That responder could either accept the offer or reject it so that both got nothing and would have to wait another hour before getting to drink.

The researchers rigged the experiment so that each participant actually played the part of the responder and was presented with an unfair offer — an eighth of the original bottle of water — that they believed was from the proposer. The researchers found that the subjects tended to reject the offer, even if they were severely thirsty, according to a statement from the Wellcome Trust.

"Whether or not fairness is a uniquely human motivation has been a source of controversy," lead researcher Nick Wright said in the statement. "These findings show that humans, unlike even our closest relatives, chimpanzees, reject an unfair offer of a primary reward like food or water — and will do that even when severely thirsty."

The study appeared Thursday (Aug. 23) in the journal Nature Scientific Reports.