Abstracts

Evolutionary origin of empathy

SHIGERU WATANABE Keio University, Japan

Empathy is the emotional response to the emotional expression of others. Darwin believed that non-human animals have a sense of empathy and wrote, “Many animals certainly sympathize with each other’s distress or danger”. Empathy for positive emotions occurs when observing how positive fortunes of others generates pleasure, and empathy for negative emotions occurs when observing the misfortune of others causes distress. These emotional responses are evolutionary adaptive, because the good fortune of others may signal positive fortune for the observer and the misfortune of others may signal danger for the observer. Empathy for negative emotion is also basis of rescue or helping behavior that serves to alleviate the observer’s distress. Empathy for positive emotion is widely observed in humans but it is rather rare in non-human animals. I present social facilitation of pleasure induced by a psychoactive drug in mice as an example of the empathy for positive emotion. In both forms of the empathy, the emotions are state-matched between the demonstrator and the observer. One important factor in the state-matched empathy is common experience between the observers and demonstrators. Pain response of demonstrators suppressed operant behavior of observers when they had experience of similar pain in their past. “Reversed empathy” or envy, occurs when distress results from observing the fortune of others. This emotional response can be considered as an inequality aversion. I display experimental works of this inequality aversion in mice. Mice restricted in small holders had stronger stress when their cage mates did not suffer the restriction stress. Either happiness or distress of observers in comparison to the emotional state of demonstrators can be inequality. Hence, free mice together with restricted cage mates may have inequality aversion. Humans feel unfairness in similar situation and the situation is aversive for them, although they feel pleasure in some case (Schadenfreude). I demonstrate experiments suggesting that the mice do not have this sense of inequality aversion. “Schadenfreude” occurs when pleasure is derived from the misfortune of others. The Schadenfreude has been considered to be human-unique emotion but I present some experimental evidence of this emotion in animals.

The negative inequality aversion or reversed empathy may cause avoidance of conspicuousness in a group and avoiding the conspicuousness should be anti-predatory behavior. The positive inequality aversion that has not been observed in non-human animals may have some function to maintain long-lasting society such as human society. In human studies, observers experienced Schadenfreude when observing failure by higher-status demonstrators. Similarly, pain response of dominant cage mates caused pleasure in subordinate mice. It may imply that there is a probability of overturning the relative hierarchical positions. These comparative studies of empathy will clarify nature of human empathy.