Mice are confronted with a challenge they would never have experienced in their evolutionary history, they have quickly established social rules to cooperate rather than fight. The discovery challenges thinking about conflict avoidance in non-human animals, and the origin of our own ethical systems.
In one of Terry Pratchett's lesser-known books, a colony of rats, having rather suddenly developed human-like intelligence, construct sophisticated ethical frameworks for living both with each other and other animals. It's tragic Pratchett didn't live long enough to learn that a simpler version of his story has been observed in action in another rodent, without his magic.
Dr Hee-Sup Shin of the Center for Cognition and Sociality, Korea and colleagues trained mice to find their way through mazes to a reward zone where the pleasure center of their brain was electrically stimulated. Pairs of mice were then put into the maze together, and the system changed so that the reward was only available if both mice entered an initiation zone at the same time. The reward was provided elsewhere in the maze, but only to one mouse. If a second mouse entered the reward zone, the first one's stimulation was cut short.
Mice might have initially responded by racing each other from the initiation point to receive the reward. Occasionally dominant individuals bullied the weaker mouse into helping trigger the reward, but always claimed it for themselves. We might also have seen mice go on strike, refusing to assist each other.
Mostly, however, as reported in Nature Communications, the mice cooperated to share the rewards. The reward zone varied randomly between the left and right side of the maze, with a light indicating its location. Most pairs reached a routine, where one took the left-zone rewards, and the other got the right. When it was one mouse's turn, the other mostly stayed behind to avoid interfering.
Sensible as this arrangement is, it has often been argued that most animals are too impulsive to develop such cooperative approaches, at least without evolutionary pressures. Known exceptions, such as dolphins, only appear to emphasize that such rule-based behavior is the preserve of the very smart. To see it emerge in mice, and without a long adaptation period, shakes that belief.
The paper proposes that impulsiveness in animals is largely related to food – something often used as a reward in experiments – particularly when the animal has been deliberately made hungry beforehand. “Food-deprived animals become impulsive and tend to choose immediate rewards,” the authors argued. Their theory is supported by evidence from a parallel study replacing brain stimulation with food as the reward. Hungry mice fought 57 percent of the time when rewarded with food, but only 8 percent for brain stimulation.