Who hates inequality?

Chimpanzees are highly sensitive
to inequity, and typically refuse to continue in interactions in which
they get less than a social partner. However, chimpanzees from stable social groups
do not respond negatively in situations in which their partners
received better rewards, whereas chimpanzees from less-established
groups show rejection rates as high as 60 percent.

Here is the full story, interesting throughout; the hat tip is to Mark Thoma.