Compared to most other animals, humans are unusual in our tendency to help each other out. We donate to charity. We give blood. We show kindness to strangers, even when we stand to gain nothing in return. This behaviour is so odd that the natural question arises: are we alone in such selflessness? And if any animal could help to answer that question, it’s the chimpanzee, one of our closest relatives.
Dozens of scientists study the behaviour of chimps, looking at how these apes act towards their peers. But the results of these studies have been frustrating for many in the field. People who watch captive and wild chimps have documented hundreds of cases of seemingly altruistic behaviour. They have seen individuals helping each other to climb walls, consoling each other after fights, sharing food, risking death to save companions from drowning, and even adopting the babies of dead and unrelated peers. Anecdotes like these suggest that chimps, like humans, behave selflessly towards each other.
But experiments have often shown otherwise. In some studies, chimps choose to help their peers retrieve out-of-reach objects rather than doing nothing. But when chimps have a choice between two equal actions – say, cashing in a token that leads to personal gain versus another that also benefits a partner – they only looked out for themselves. One paper bore the title “Chimpanzees are indifferent to the welfare of unrelated group members”. Another concluded that “chimpanzees made their choices based solely on personal gain”.
Collectively, these studies championed a view of chimps as reluctant altruists, who only act selflessly in response to pressure, and who generally don’t help unfamiliar chimps, “even when they are able to do so at virtually no cost to themselves”. But Frans de Waal from the Living Links Centre at Emory University thinks that this portrait is wrong. He says, “The authors of these studies moved from not finding evidence for prosocial choice to thinking they had proven its absence.”
De Waal thinks that the previous tests handicapped the chimps by putting them in situations that masked their altruistic tendencies. They couldn’t communicate, they had to cope with complicated equipment involving levers, and they often sat so far apart that they had little understanding of how their choices affected their fellows. With his colleague Victoria Horner, de Waal designed a new experiment to account for these problems. And, lo and behold, chimps spontaneously helped their partners, even without any prompting.
The team placed two chimps in different compartments, separated by a mesh partition. One chimp could choose between two tokens – a “selfish” one that earned them alone a reward, and a “prosocial” one that provided the same reward to a partner too. They picked the tokens from a large bucket and depending on their choice, Horner would reward one or both of the animals with fruit, wrapped in paper.
Horner specifically designed the set-up so that both chimps could see “how choices were made and how these choices affected them.” On average, the chimps chose the prosocial token around 59 percent of the time, higher than expected by chance. When they were placed in the same situation without a partner, they only picked the prosocial token around 46 percent of the time, no different to a random choice. Their selfless tendencies didn’t change if they had worked with their partner before, and neither rank nor kinship affected their behaviour.
Horner writes, “Offered a free choice between a prosocial and selfish option, chimpanzees overwhelmingly favoured the former to the advantage of their partner.” ‘Overwhelmingly’ may be too strong a word given the relatively small size of the effect, but the result is still statistically significant and contradicts those of earlier studies. It shows that subtly tweaking elements of an ape experiment can have a big impact on the behaviour of the animals.
For example, Horner wrapped the food rewards were wrapped in paper so its constant presence wouldn’t distract the chimps. She gave the animals a bucket of tokens rather than the standard approach of a pair of levers or handles, so they wouldn’t develop a preference for any one choice. And perhaps most importantly, she allowed them to sit close to one another in plain sight. In other studies, chimps sat metres apart, or were separated by a glass barrier. In many cases, they barely communicated at all. That wasn’t the case here – the chimps interacted extensively.
While other scientists have claimed that chimps only help their peers when harangued or prompted, Horner found the opposite. When the partner drew attention to itself by way of scratching or grunting, the main chimp was more likely to reward both of them with food. But if the partner behaved more brazenly, by staring at the tokens, hooting or begging, they were less likely to get fed.
John Mitani, who has spent a lot of time studying wild chimps, says “I buy the results, but am not entirely surprised. They are in line with some of the things we see in the behaviour of wild chimps.” However, Mitani adds, “I think that an important issue is left off the table. The impressive and unusual thing about human behaviour is that we occasionally go out of our way to help others, some of whom can be total strangers. It would be interesting to see how chimps perform with strangers [but] I doubt that such tests would be possible because the chimps do not react kindly to strangers.”
Sarah Brosnan, who was involved in previous studies that found negative results among chimps had also worked with de Waal on experiments that found signs of selfless behaviour in capuchin monkeys. She is excited by the fact that Horner’s new study in chimps closely mirrors the methods that she used with capuchins. “It makes it easier to compare results. It’s particularly interesting that these chimpanzees, unlike the capuchins, seem to be unaffected by social relationship and kinship,” she says.”
But Brosnan also notes that capuchins showed altruistic behaviour in more complicated set-ups involving levers – the same set-ups that apparently handicap the social behaviour of chimps. “To me, the really interesting question is what causes the difference in response,” she says. “I suspect the answer to this question will help us to better understand the cognitive mechanisms underlying the behaviour, and hence how prosocial outcomes evolved, across the primates.”
In light of experiments like these, and observations in the wild, why has the portrait of the indifferent selfish chimp become so popular? “My belief is that many social scientists are uncomfortable with the full implication of Darwinian evolution, which is mental continuity,” says de Waal. “They keep looking for the human spark and prefer saltationist arguments [which suggest a big leap from one species to another – Ed].” As an example, in her 2005 paper, Joan Silk wrote, “The absence of other-regarding preferences in chimpanzees may indicate that such preferences are a derived property of the human species, tied to sophisticated capacities for cultural learning, theory of mind, perspective taking and moral judgement.”
De Waal says, “They have had their try with tool use, theory of mind, culture and the like, and now have jumped on altruism and cooperation as the place where major differences will be found. I am sure they exist, but the whole evolutionary framework of altruism research (kin selection, reciprocity) is based on animals for a reason, which is that we are not really that different.
“Major journals like the saltationist argument, readerships outside of biology like it, and as a result negative findings have gotten more press than they would in any other field. Cancer researchers would not get excited by negative findings of drugs that don’t work. As soon as we enter into the distinctions between humans and apes, however, absence of evidence takes on a new meaning. It’s the never-ending desire to find the holy grail of humanity. Blurring of the boundary upsets many and is therefore, at the moment, a major movie plot.”
Reference: Horner, Carter, Suchak & de Waal. 2011. Spontaneous prosocial choice by chimpanzees. PNAS http://dx.doi.org/10.1073/pnas.1111088108
Image by Dullhunk
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