Altruisme, quel est le propre de l'humain ?

Published online: 25 June 2007; | doi:10.1038/news070625-4

Is it a chimp-help-chimp world?

Clever experiment shows altruism in great apes.

Kerri Smith

Videos show chimps and human infants helping each other out. © Warneken and Tomasello

Humans are often thought of as the only truly altruistic species. We help others out - by giving blood, donating to the poor, or committing to recycling - for no immediate payoff, and often at a cost to ourselves.

But evidence is gathering that we might not be alone. Felix Warneken and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have shown that chimpanzees will do favours for unrelated chimps - even when they do not get rewarded for it.

Previous studies have refuted the idea that chimps are so giving. In 2005, anthropologist Joan Silk of the University of California, Los Angeles, found that when she presented chimps with the choice of getting food just for themselves, or for their entire group, they showed no preference for feeding their pals as well.

But other work has shown that chimps can have a non-selfish streak. In a study published in Science last year, a Leipzig team reported that chimps would help their human keepers retrieve a pen that they had dropped - an action with no direct benefit for the chimp.

That study involved chimps helping out human carers whom they were familiar with - and who had on other occasions provided the chimps with food. To get rid of these complications, the Leipzig team replicated the pen-dropping experiment with unfamiliar humans. As they now report in PLoS Biology, the chimps still chose to help out.

Let me at that banana

The team did another experiment too, to clarify whether chimps would be altruistic to others of their own kind without a scent of reward. They placed one chimpanzee in a room with a closed door leading to some bananas that it had seen, and a second chimp in a position where it could not see the bananas, but could open the door. When the first chimp struggled to open the door, the second chimp watching the struggle (but unaware of the reason for it), would pull a chain to open the door. In trials, chimps would help out a struggling mate nearly 80% of the time, even without knowing that food was involved.

Warneken suggests that this clever experimental setup proves what he and others already thought chimps were capable of, but hadn't been able to demonstrate before. "We should move away from the question 'is altruism there?' to the question 'under what circumstances do chimps display this behaviour?'," he says.

Silk says she's impressed with the experiment. "This raises a bunch of questions about the context and the motivation of chimps to behave in a way that is beneficial to others," she says. "What does this mean to them?"

Young and sweet

But Silk notes that the results still might not show true altruism that exists across the species. She wonders, for example, whether there is something special about these chimps and how they have been raised since their capture from the wild. She would like to see the experiment done with other chimps - or for these chimps to have a go at her experiment.

She also wonders whether the age of the chimps makes a difference. Whereas Warneken's group worked with young chimps, Silk's experiments used older animals. Chimps might get more selective in who they help as they age, she suggests.

Warneken is convinced that his experiments offer proof of chimp altruism. And if chimps can do it, the roots of the tendency in our own species might go deeper than previously assumed. "Culture and education are not the only origin of these altruistic tendencies," says Warneken. Human society, he says, has cultivated a trait that was already present, rather than inventing it anew.

References

1. Silk J., et al. Nature, 437. 1357 - 1359 (2005).
2. Warneken F.& Tomasello M. Science, 311. 1301 - 1303 (2006).
3. Warneken F., et al. PLoS Biology, 5. e184 (2007).

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Published online: 3 July 2007; | doi:10.1038/news070702-4 / http://www.nature.com/news/2007/070702/full/070702-4.html

Generosity among rats

Rats do unto others as they have been done to.

Louis Buckley

A helping paw: rats are more generous when another rat has helped them out. Punchstock

Rats that benefit from the charity of others are more likely to help strangers get a free meal, researchers have found.

This phenomenon, known as 'generalized reciprocity', has only ever been seen before in humans. A good example, says Michael Taborsky of the University of Bern, Switzerland, is what happens when someone finds money in a phone box. In controlled experiments such people have been shown to be much more likely to help out a stranger in need following their good luck.

In humans, such benevolence can be explained by cultural factors as well as by underlying biology, says Taborsky. But if similar behaviour can be found in other animals, he reasons, an evolutionary explanation would be far more likely.

To test for this behaviour in animals, Taborsky trained rats to pull a lever that produced food for its partner, but not for itself. Rats who had received a free meal in this way were found to be 20% more likely to help out an unknown partner than rats who had received no such charity¹.

Taborsky believes this behaviour isn't confined to just rats and humans. "I'm convinced generalized reciprocity will be very widespread and found in many different animal species, as our study suggests that an underlying evolutionary mechanism is responsible."

"Generalized reciprocity is certainly underappreciated in animals," notes Laurent Keller, an evolutionary biologist at the University of Lausanne, Switzerland. But with so little data in this area, he adds, "it is very difficult to make predictions about how prevalent it's likely to be."

Survival of the friendliest

Explaining why animals cooperate has long been a tricky area for evolutionary biologists. According to darwinian evolution, organisms are adapted to maximize their individual chances of survival, so how is it possible to account for acts of charity?

Among family members, it makes sense for one animal to help another in order to help their shared genes to get on in the world.

But when it comes to helping non-family members, things are more complicated. It might make sense for one animal to help another in exchange for receiving help themselves later on. But this is open to abuse by cheats who are happy to take, but not to give in return.

Highly intelligent animals - including humans - can judge whether or not to give help based on the individual track record of a specific potential partner. But this kind of 'direct' reciprocation between two individuals only happens under restricted conditions, says Taborsky. "Animals have to meet frequently and have to remember what other individuals have done and how they acted in the past. That means animals have to possess high cognitive abilities. And for these reasons it hasn't been demonstrated very often."

Another strategy, called 'generalized reciprocity', is for an animal to assume that its most recent interaction with any other individual is representative of how the whole community usually behaves. In that case, an animal only has to remember its last experience. "It's a simpler mechanism and therefore more likely to be evolutionarily important," says Taborsky.

Not-so-dirty rats

Taborsky thinks he has seen both types of reciprocity in his rats. In addition to being 20% more likely to help out an unknown partner if they had received a bit of charity, his study shows that rats were more than 50% more likely to help a specific rat who had helped them in the past¹.

Taborsky thinks that it is likely that the two forms of reciprocity work together. If an animal can remember how generous another individual is it will use this information to decide whether it's wise to cooperate. But if not, then it can base its decision on more general recent experience - how helpful other animals have been towards it in the recent past.

Other researchers point out that because rats typically live in family groups, it's hard to discount the idea that they're just trying to help their relatives out.

"What we need to understand now is the physiological and neurological mechanisms responsible," says Taborsky. He suspects that hormonal changes in response to charity might be behind the tendency to cooperate. "We are going to look at hormonal regulation, and we're also looking at other animals - cichlid fish at the moment."

Reference : Rutte, C. & Taborsky, M. PLoS Biol. 5 , e196 (2007).