I attended a talk this morning by Frans B. M. de Waal, who discussed the extensive results from his research team on cooperative and ethical behavior among non-humans.
The audience laughed in delight at experiments that showed an angry capuchin monkey demanding equal pay for equal work, a chimpanzee handing the correct tools to another chimpanzee so the latter could complete an assembly operation, elephants coming up with surprising inventions to help each other with cooperative tasks, and an ape refusing a reward from a human unless a equitable share was also given to another ape.
But there was one point where the audience just went thoughtfully silent. Describing an experiment that showed that a mouse becomes significantly more sensitive to pain after it has seen another mouse in pain (an experiment that, needless to say, raises its own ethical issues), de Waal mentioned that the effect is only observed if the mouse knows the other mouse.
It may have been the first time most people in the audience had ever thought about friendship among mice.