Chimpanzees have been found to share yet another of the characteristics we think of as quintessentially human: the capacity to weigh intent after suffering a wrong.
If someone has hurt us the question of whether it was deliberate or an accident is fundamental to human response. It’s why murder and manslaughter are separate crimes with very different penalties. Ignoring the motivations of others and punishing someone for something they couldn’t control is deeply frowned upon. Yet to consider such issues requires a sophisticated theory of mind usually considered beyond animals.
However, two studies published together in Biology Letters reveal chimpanzees are sometimes capable of understanding the distinction, can take it into account, and apply it to humans as well as their kin.
Professor Jan Engelmann of the University of California, Berkeley and co-authors had human experimenters offer food items to chimpanzees at a sanctuary. The chimpanzees had been taught the foods were theirs in return for returning a tool they’d been given. They could decide whether to accept the food and perform the task or refuse it.
In the first experiment, two foods were displayed. The experimenter had previously established which food an individual chimpanzee preferred. In some cases, the foods were positioned so the experimenter could reach both, but in other scenarios, the preferred food was locked in a box the experimenter would unsuccessfully attempt to open, a fact the design of the experiment clearly demonstrated to the chimpanzee.
Chimpanzees who saw the experimenter had no choice but to give them the less desirable food, were more inclined to accept it than when the person was wilfully offering them second-best. The researchers also observed the chimpanzees’ emotional responses and reported more indications of resentment, such as spitting at the experimenter, when they judged their deprivation was deliberate.
“This is, to our knowledge, the first demonstration that chimpanzees, like humans, evaluate social treatment not only in terms of outcome—e.g. whether they received a preferred or a non-preferred item—but also with regard to its causal history,” the authors write. A previous study produced something similar, but weakness in experimental design left room for alternative explanations.
The second experiment was more subtle. In half the trials one experimenter hid a preferred food item where another human could not see it, but the chimpanzee could. Thus as far as the person providing the food knew, they were giving the chimpanzee the best that was on offer. In the other half, the experimenter was clearly aware of the preferred item and chose not to provide it.
The apes were not similarly forgiving in this case. Their theory of mind apparently did not extend to understanding that the human didn’t know about the tasty treat the chimp could see but the human could not. In this experiment, the reactions to being given the second-best food were the same whether the human knew there was an alternative, or if they did not.
Some people might be relieved to learn that chimpanzees’ knowledge of human psychology is not so sophisticated as to be able to grasp what the human does or does not know. They may be closer to us than we think, but not that close. Anyone feeling this way, however, might want to consider how many humans would perform better on the second test, grasping that someone who disappointed them did so out of ignorance, rather than malice.