How chimps, monkeys and humans compare on a level playing field

February 9, 2011 by Lin Edwards report

( -- A problem faced by scientists comparing the mental abilities of humans, chimpanzees, apes, and monkeys is that the humans are tested by their own species and understand the requirements of the tests, while the other primates are tested by a different species (humans) and have to work out what they are supposed to do. This uneven playing field can distort the results, and so researchers in the US have designed experiments that remove the advantages humans usually have.

Psychologist Sarah Brosnan of the Language Research Center at Georgia State University tested humans, chimps, and capuchin monkeys with a decision-making "assurance" game that ensured no participants had an advantage over the others. The game was a variation of an often-used game called "Stag Hunt," which has two participants who can choose to hunt either a hare or a stag. A hare can be killed by a single hunter for a small reward, but killing the more highly-rewarded stag needs both participants to choose the stag. The aim of the game is for the participants to work out how to get the greatest reward.

Most studies of this type are designed for humans and then adapted for the other primates, but Dr Brosnan reversed the process, designing the game for the monkeys and chimps and giving the humans no instructions other than telling them they would make decisions based on tokens, and would be paid in quarters or dollars each round. They also had to work out the game non-verbally, and the tokens did not have pictures of hares or stags, but were either blue or red.

The research team tested 24 , 52 humans (all students), and eight . All the subjects had previously participated in similar games with winnings paid in food or money. All subjects were tested in pairs of the same species and were seated next to each other. In most studies of this type the pairs are selected via computers and do not sit next to each other.

The game began with each member of the pair handing over one of the two tokens to the researcher. Dr Brosnan then held up the tokens so each could see what their partner had chosen. She then gave participants a reward for a match, in the form of money for the humans, or fruit for the monkeys and chimps, with the greatest amount of money or fruit for a Stag-Stag match.

The capuchins generally had no strategy, with only one of the six pairs making Stag-Stag choices more often than expected by chance. The chimpanzees matched their partner more often, but chose Hare-Hare as often as Stag-Stag. The students matched Hare-Hare and Stag-Stag slightly more often than either of the other groups. A third of the human pairs selected Hare-Hare and then subsequently stuck with the low reward each round, suggesting they were resistant to risk, or thought they had beaten the game.

The results mirror the social complexity of the species, with human social life the most complicated, followed by chimps, which hunt in groups and have a complex social life. The capuchins are the least social of the species, and are the most evolutionary distant from humans. Dr Brosnan said the results provide preliminary evidence that human behavior in cooperative games could be part of an evolutionary continuum, and share the same foundations.

The results were different for the three species but not as different as the researchers had expected. For example, only five of the 26 student pairs chose Stag-Stag, which was only a slightly higher rate than the chimps. When humans have the rules of the game explained to them and they are allowed to speak, they would normally demonstrate 100% cooperation. Their poor results of only 20% show humans are extremely reliant on language.

The paper was published this week in the Proceedings of the National Academy of Sciences (PNAS).

More information: Responses to the Assurance game in monkeys, apes, and humans using equivalent procedures, Sarah F. Brosnan et al., PNAS, Published online before print February 7, 2011, doi:10.1073/pnas.1016269108

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5 / 5 (3) Feb 09, 2011
Humans played for low value money but chimps and monkeys, fruit. I wonder if a piece of food like chocolate had been used if the results would have been different. Money is deferred gratification, chocolate is immediate.
5 / 5 (2) Feb 09, 2011
In real life, you know what your options are and have the potential to cooperate and achieve by working together. This holds the same for people and chimps. If you aren't aware that there is any reward, but happen to stumble upon one, you will be pleased and accept the reward you see. It would actually only be greed that would lead you think - hmmm, maybe there's a bigger reward out there, so let's ditch the good thing we just happened upon.

Doesn't this test really just measure ability to cooperate?
5 / 5 (1) Feb 09, 2011
Rethinking my last post, I guess there is intelligence required in recognizing that combinations cause reward - so there is more being tested than cooperation.

One more thought - the humans knew they were being tested and that there was a reward, while the chimps may or may not have. This can also lead to a difference in result.
5 / 5 (1) Feb 09, 2011
Doesn't this test really just measure ability to cooperate?

I think it also tests inquisitiveness. The rules aren't known to the participants (but they do have the knowledge that there ARE participants). It is astounding that the students didn't try to experiment more to map out the rules of the game themselves in order to maximize gains.

The above also brings up another question: While the students were aware that others participated in a gane setup the monkeys might not have been aware that their actions (and those by their 'partner') were in a common context.

So I think this tests tests context awareness as much as it does intelligence (i.e. if you rely on its intelligence-predicting abilities you may be relying on a biased test)

However this seems rather hard if you never get to see the
3.5 / 5 (2) Feb 09, 2011
Humans played for low value money but chimps and monkeys, fruit. I wonder if a piece of food like chocolate had been used if the results would have been different. Money is deferred gratification, chocolate is immediate.

I don't agree with this at all. I think money is a much greater motivator than food.

Unfortunately, whats not clear in the article is what happens when the stag-hare choice is made. If the person choosing the hare gets a reward but the person choosing the stag gets nothing, then the results make sense to me. If you pick stag and get nothing you'll try hare. If you then get rewarded there is not a whole lot of reason to go back to stag. 20% of humans choosing stag-stag seems a bit low, but it probably just reflects the ones who happened to choose stag-stag on their first try.
5 / 5 (1) Feb 09, 2011
Isn't the ability to communicate a central piece of intelligence. A truer representation of this game would be if in all 3 cases the pairs were inhibited from viewing, hearing, etc to each other. Or all 3 pairs were given the chance to use their communication abilities to their greatest potential.

Without verbal communication or even human non verbal communication, this test, in my mind, really only tests the reasoning ability of the subjects, by getting a match, you get a reward. Were the humans allowed to communicate non verbally? If so, I know I would look at the other person, give a reaction of being only slightly pleased with the outcome. Show the other the color of chip that corresponded to stag in an indication that I wanted to see what happened in other combos. All though it says "in most studies" so no definitions on this study per say.
5 / 5 (1) Feb 09, 2011
An interesting variation of this experiment would be to see how the participants react if the rules change during the game. For example, at some point maybe hare-hare becomes the best choice. This happens in the real world all the time, as the environment and circumstances change, organisms must be able adapt to the changing environment. A strategy that worked in one situation might not work in another, and vice versa. My question is whether humans are better at recognizing when the rules have changed and changing their strategy? This kind of thing has actually been tested, by tests like the wisconsin card sorting test. And there have been interesting results. For example, a specific brain region controls a person's ability to change their strategy/recognize a change in the rules of the game. Also, depressed people have a harder time recognizing changes and changing their strategy.
1 / 5 (1) Feb 10, 2011
This a stunning display of lacking something better to do with your time and PHD. I surely hope this was not a million dollar stimulous project.
not rated yet Feb 10, 2011
That's why they have a PhD and you don't. They know what kind of value such research can bring:

- validation of game theory for social interaction
- cognitive abilitis of brains which are developed to various extents
- that above ties directly into the neurosciences (which parts of the brain are more highly developed in which species and can therefore be hypothesized as the seat of such decision making/context awareness abilty)
- ...

It certainly beats subsidizing the gas for your car (which is a multi-BILLION dollar stimulus) subsidizing your

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