Chimpanzees have a bad reputation. Maybe it's because humans have a thing about wanting to feel unique among primates. Some have argued that humans are the only species that truly behaves altruistically, the only species that actively helps out other individuals even when there is no direct benefit. Despite mounting evidence that other animals, including non-human primates, have various forms of theory of mind, many still believe that human altruism exists because we - and we alone among all the animal kingdom - can understand the goals of others. Or, if there are other animals that can understand the goals of others, perhaps we somehow do it more readily.

In a new paper just published in PNAS, primatologist Shinya Yamamotoa and colleagues point out that while chimpanzees are known to help others, they don't usually help when it would mean giving up things like food, even if they've got more food than they need. Even between a mother and her infant!

Why do chimpanzees seem so reluctant to help others? One possible explanation is that they're unable to understand the goals of another individual, resulting in an inability to create any sort of shared intentionality between two individuals. To that end, the researchers write, "many still believe that humans are unique in this respect because we are the only animal species endowed with unique 'theory of mind' abilities enabling us to understand the goals and to share the intentions of others."

Yamamotoa and the other researchers set up an experiment designed explicitly to address this possibility. The first chimpanzee was given a task to accomplish in order to receive a juice reward. The task required the use of one of two types of tools: a stick or a straw. The stick and the straw, however, as well as five other items were found not in the first chimpanzee's booth, but in the second chimp's booth. There was a small opening between the two booths where the second chimp could pass the necessary tool to the first. By itself, this could test whether or not the second chimp was willing to help the first chimp.

But to see whether the ability to understand the goal of another individual modulates the potential to help, the researchers created two further conditions: half the time, the barrier separating the two booths was a transparent window, and half the time it was a completely opaque wall. If chimpanzees modulate their responses to a help request based on whether or not they can see the goal of another individual, then they should give the appropriate tool more often when in the transparent window condition.

During the transparent window condition, the chimpanzees were more likely to offer up the appropriate tool (e.g. a stick during the stick condition, or a straw during the straw condition) than any of the other tools. This result itself shows that the chimpanzees were able to understand which tool their partner would need in order to solve a given task. Importantly, ninety percent of tool offers occurred only after a request was given by the first chimpanzee, suggesting that while chimpanzees may not spontaneously engage in helping behaviors, direct requests are effective in soliciting assistance.

The results from the opaque window condition might provide some insight into how the chimps determine which tools to provide when asked for help. As in the first condition, chimps were extremely likely to offer a tool after a request was made. In fact, one of the objects (even if not the useful one) was given following a request 98.5% percent of the time, on average. While they were more likely to offer one of the two useful tools - the stick or the brush - compared with the other items, the tool that the first chimpanzee needed was not predictive of the tool they were given. In other words, the chimps were not able to infer the precise goals of their partner. They were only able to understand that their partner needed a tool, in a generic sort of way. The one exception to this trend was a chimpanzee named Ayumu, who actually pulled himself up to see through the small window, effectively turning this "cannot see" condition into a "can see" condition.

The chimps' willingness to help was similar in both conditions. That is, following a request for help, the chimpanzees were equally likely to offer a tool whether or not they could see their partner's situation. While a request might be sufficient to motivate a chimpanzee to help, requests did not provide enough information for the chimps to help effectively. The researchers point out that Ayumu's behavior - selecting the appropriate tool only after looking through the hole in the wall - further reinforces the notion that chimps require visual information in order to help. The researchers conclude, "even without shared intentionality and sophisticated communicative skills, such as language or pointing, chimpanzees can understand others’ goals when situations are visibly obvious and understandable."

In a sense, though, the findings from this experiment are a bit contradictory: even when they could not visually assess their partner's situation, the chimpanzees were willing to help, and even persisted in offering multiple tools. But when given visual access to their partner's booth, they rarely helped unless directly requested. That is, the ability to infer a partner's goals is not the limiting factor in chimpanzees' altruistic behavior. So...what is?

Yamamoto S, Humle T, & Tanaka M (2012). Chimpanzees' flexible targeted helping based on an understanding of conspecifics' goals. Proceedings of the National Academy of Sciences of the United States of America PMID: 22315399

Chimpanzee photo source, used under Creative Commons license.