Scientists from the UK and the USA conducted a study that demonstrated that various species of monkeys, including chimpanzees, capuchins, saimiris, and marmosets, do not refuse food even when they observe a conspecific receiving a more valuable reward in 25 or 50 percent of cases.
The results obtained may indicate either the ability of these animals to accept inconsistent inequality or point to possible limitations of the experimental test itself.
This scientific work was officially published in the American Journal of Primatology.