Small groups of chimpanzee can take collective action. But two scenarios here divided their reactions into differing types, related to personalities and the "quality" of their relationships.

CAPs are collective action problems. They come at a cost. They result in a shared good in which other players can share. A free-rider is the most successful participant as they exert no effort but achieve the benefit. A female lion who fails to take a lead role in the chase is the classic example. (Just don't mention some pride males!)

There is therefore some disincentive for these chimpanzees to act in this set of behavioural investigations. Anna-Claire Schneider and her colleagues worked with the chimpanzees in the Max Planck Institute in Leipzig, and publish their study, How chimpanzees solve collective action problems, in the Proceedings of the Royal Society B: Biological Sciences today.

To overcome CAPs, two questions are being faced. How could a mechanism avoid an" impasse;" and what governs the adoption of a successful strategy( or is there a pattern in the making of decisions by the chimpanzees?) If we take wild chimpanzees when they hunt colobus monkeys, we can observe that a male has a better chance of gaining a scrap of meat if the group is larger.

Deterrents to action include the possibility of injury or loss of energy. They would also include the free-riding option in the largest groups, both hunters and non-hunters being equally likely to gain - so why hunt? It has been suggested that individual incentives for certain "impact hunters" govern the start of a hunt. The possible factors are dominance, skill, strength and agility, with personality one of the most obvious.

Close up of the action box and collecting box used in experiment 1; Credit: © Proceedings of the Royal Society B: Biological Sciences

"The Volunteer's Dilemma", is the obvious situation in which if you don't volunteer for an action, nobody else may do so either. The reward, whatever it is is lost, unless one individual acts. 3 rooms with juice dispensers leading to the opposite end of the apparatus were provided for groups of animals. This formed the first experimental situation, with 2/3 chimpanzees.

In the second experimental series, a reduction in the amount of the reward was the cost. The number of chimpanzees was either 3 or 6. Any two individuals could pull two ends of a rope to make up to 320 peanuts spray into a separate room through a funnel dispenser.

Close up of the peanut dispenser used in experiment 2. Note that the peanuts spray into the room opposite where the rope ends are pulled forcing subjects to climb up to and cross an overhead raceway to transition from action to reward access; Credit: © Proceedings of the Royal Society B: Biological Sciences

7 females, aged 7-16 years and 5 males aged 5 - 33 live in Leipzig in social groups of six individuals (3 subjects) and seventeen individuals (9 subjects.) Four groups of three were used in the investigations, avoiding any stressful or aggressive possibilities by taking the advice of the animals' keepers. The keepers also contributed their known dominance hierarchy for each group. The small numbers used and the qualitative nature of some outcomes here mean that we have to take the results with a pinch of salt.

However, there is no denying a positive relationship between higher rank and the tendency to push the juice button more. Dominant individuals could be relied upon to get a worthwhile reward, whether they pressed the button or not.. Subordinates rarely did. In the 3 trough experiment, rivalry was increased. Free-riders were subordinates who were in highly tolerant groups. The obvious situation with low tolerance by the dominant in a pair and a fearful subordinate resulted in little reward for the subordinate.

The second experiment again involved 12 individuals, divided repeatedly into 6 groups of 6. Sub-divisions of these sixes consisted of four groups of three. Most pre-tests of pairs (88%) were successful with almost half making no mistakes. In the triads and sextets, 28% and 22% did not pull in trials. "The Volunteer's Dilemma" once more applied. The cost to subordinates was obviously higher, but the dominant paid a higher cost for pulling because they could not occupy the central position at the dispenser and had to feed from the floor. Subjects quickly adapted their positions according to what they experienced. Sextets had low pulling rates, certainly after a few trials. Individual "impact-pullers" occurred, pulling at any trial. Their personality obviously suited this experimental situation and perhaps the monkey catching "impact-hunter" situation too. Gain for others is likely in both situations.

Whereas in expt. 1 the dilemma was usually overcome, expt. 2 provided sextet conditions where enthusiasm waned. Every individual could share in rewards, but the dominant could sit in front of the dispenser and receive the "lion's" share. Subordinates had little incentive to pull because five other's could receive more nuts than themselves. They would also have to somehow recruit another subordinate to comply (and receive less peanuts too.) As dominance would have little influence here, individual motivation seemed to be responsible for the successes. Two "impact-pullers" in the same group would obviously increase the chances of success while one of them could have catalysed the action of one more individual to cooperate.

So the dilemmas were overcome by chimpanzee behaviours. Except where dominants pay a higher cost, the mechanisms used by the groups produced collaboration. This is where qualitative description of the actors who were impact-pullers and their colleagues, came into play. Individuals contacted these actors when noisy individuals caused a mild hiatus during the expt., so anthropomorphic conclusions could be made. Humans would take turns, but perhaps not, if actions reduced the potential for receiving a reward.

The next CAP scenario to be tested? Something that reflects the payoff the wild chimpanzee gets when he hunts..