Chimpanzees may be cute, but they're selfish sods, argues Mathew Iredale
We are used to be being told by the latest scientific research how similar we are to our ape cousins, especially chimpanzees.
Tool use, once thought to be a uniquely human activity, has been observed many times in wild chimpanzees. More extraordinary is the fact that captive chimpanzees have been taught sign language, and in some cases have taught it to their offspring. And research into the chimpanzee genome has just been published which suggests that we share as much as 99% of our functional DNA with chimpanzees.
But despite all these examples, significant differences still exist between humans and chimps. Humans are a very social species. Experimental evidence indicates that people willingly incur costs to help strangers in anonymous one-shot interactions, and that altruistic behaviour is motivated, at least in part, by empathy and concern for the welfare of others. But such behaviour does not appear to be shared by chimpanzees, in which cooperative behaviour is mainly limited to family members and reciprocating partners, and is virtually never extended to unfamiliar individuals.
This conclusion has recently been confirmed by a study by the anthropologist Joan Silk which was designed to determine to what extent individual chimps will take advantage of opportunities to deliver benefits to familiar but unrelated individuals at no material cost to themselves. Each chimp was presented with an apparatus that gave him a choice between two alternatives. If the chimp chose option one, he received a food reward and so did a second chimp in a different, but highly visible, enclosure. If the first chimp chose option two, he still received a food reward, but the other chimp did not.
If chimps show concern for the welfare of others, one would expect to see them choosing option one more often than option two, for they get the same reward regardless of which choice they make, but with option one their fellow captive also gets a tasty morsel. In short, as Silk says, “All they had to do was be nice... It's not as if we were asking them to give blood or write cheques to tsunami victims.”
But what the study showed was that the chimps were no more likely to choose the generous option than the selfish one. They just didn't care about being nice.
Perhaps this should come as no surprise, as chimps generally help non-family members only if there is something in it for them, and not just “to be nice”. Put another way, their behaviour is strongly driven by direct reciprocity.
Direct reciprocity can best be captured by the principle “You scratch my back and I'll scratch yours” and it is the driving force of a large part of chimpanzee social behaviour. If Silk's study had been carried out using just two chimpanzees then a sense of reciprocity might have developed between them, and there would have been a higher incidence of choosing option one by each chimp. But as the study was carried out with one group of 7 chimps and another group of 22 chimps, direct reciprocity was unlikely to develop.
It might have been a different matter if chimp behaviour were also influenced by indirect reciprocity. Indirect reciprocity can be summed up by the principle: “You scratch my back and I'll scratch someone else's” or “I scratch your back and someone else will scratch mine”. But there is little or no evidence of indirect reciprocity amongst chimpanzees. And a recent review of the literature relating to the evolution of indirect reciprocity by the mathematical biologists Martin Nowak and Karl Sigmund helps to explain why this is so.
Direct reciprocity does not require the same intellectual or linguistic abilities as indirect reciprocity. Imagine that chimp A has some food and chimp B does not. If A gives some of his food to B then he will expect to get something in return. Most obviously, at a later date when B has some food and A does not, A will expect B to give him some. This is a basic reciprocal relationship. If B decides not to reciprocate, then A may try to punish him in some way, either through the use of physical force or simply by not cooperating with him in the future. The point to note here is that even though the chimps are unable to speak it does not affect the outcome, for better or worse, of the relationship between them. Nor does this relationship require any intellectual skills beyond remembering that “I gave B some food” (for chimp A) and “A gave me some food” (for chimp B).
Indirect reciprocity, by contrast, does require significant intellectual and linguistic skills. It requires linguistic skills because it is based upon reputation, and for my reputation to be established and to grow requires that individuals are able to tell each other what I did.
It requires significant intellectual skills because instances of indirect reciprocity are far more complex than instances of direct reciprocity. As Nowak and Sigmund state:
Indirect reciprocity requires information storage and transfer as well as strategic thinking and has a pivotal role in the evolution of collaboration and communication. The possibilities for games of manipulation, coalition-building and betrayal are limitless. Indirect reciprocity may have provided the selective challenge driving the cerebral expansion in human evolution.
If my act of kindness towards a stranger is witnessed by others, they can go off and tell their friends about it and so my reputation will grow. People will learn that I am a nice person and so be more inclined to help me should the need arise. But if my action is misinterpreted by some of the witnesses, or one of the witnesses wishes to harm my reputation, then some people may receive conflicting or false information about me.
A further complexity is added if the person is a known non-reciprocator. If Bob has been unhelpful or uncooperative in the past and I decide against helping him, then surely my own reputation should not suffer, even though I am refusing to help someone? But if I do decide to help Bob, should my reputation decrease, because I may be encouraging his bad behaviour, or should my reputation increase, because I am being helpful to someone, even if it is Bob?
In such situations a moral dimension is added to the mix. People are required to make a judgement about whether Bob should be helped or not, and whether my reputation should increase or decrease if I decide to help him (or to not help him).
From this we can see the beginnings of a possible explanation as to why it is humans who have developed a sense of morality and not other species. Direct reciprocity does not require any moral judgement to be made. It is, in a sense, just a very sophisticated variation of a symbiotic relationship. But indirect reciprocity is another matter entirely. Although at one extreme it can be simple and without moral content, at the other end it can be highly complex and involve very complicated judgements about right and wrong. And this clearly requires high intelligence and considerable linguistic abilities.
All in all, interpreting indirect reciprocal relationships is a far more complex matter than interpreting direct reciprocal relationships. For this reason Nowak and Sigmund are surely right when they state that “the intricate complexity of indirect reciprocity provided the selective mould for human language and human intelligence.” And, quite possibly, human morality as well.
Suggested reading
“Chimpanzees are indifferent to the welfare of unrelated group members”, Joan Silk et al., Nature , volume 437 (27 October 2005).
“Evolution of indirect reciprocity”, Martin Nowak and Karl Sigmund, ibid.
Everything you'd ever want to know about Mathew Iredale is at www.mathewiredale.info