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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cooperative pulling paradigm | 5/10 | https://en.wikipedia.org/wiki/Cooperative_pulling_paradigm | reference | science, encyclopedia | 2026-05-05T09:49:48.882099+00:00 | kb-cron |
Orangutans (Pongo pygmaeus) are tool-using apes that are mostly solitary. Chalmeau, Lardeux, Brandibas, and Gallo tested the cooperative capabilities of a pair of orangutans, using a device with handles. Only through simultaneous pulling could the pair retrieve a food reward. Without any training the orangutans succeeded in the first session. Over the course of 30 sessions, the apes succeeded more quickly, having learned to coordinate. Across trials the researchers found an increase in a sequence of actions that suggested understanding of cooperation: first looking at the partner; then if the partner holds or pulls the handle, starting to pull. The researchers also concluded that the orangutans learned a partner had to be present for success. For example, they observed that time spent alone at the apparatus decreased as the trials progressed. In some instances one orangutan pushed the other towards the free handle, soliciting cooperation. The researchers observed an asymmetry: one ape did all the monitoring and coordinating, the other one seemed to simply pull if the first one was present. Rewards did not have to be shared equally for success to appear, as one orangutan took 92% of all food. This ape anticipated the falling of food and stuck his hand out first, before recruiting help from his partner. Chalmeau, Lardeux, Brandibas, and Gallo concluded the apes appeared to understand the requirements of the cooperative task.
==== Capuchins ====
Capuchins (Sapajus apella) are large-brained monkeys that sometimes hunt cooperatively in the wild and show, for nonhuman primates, unusually high levels of social tolerance around food. Early experiments to prove their ability to cooperate were unsuccessful. These tests involved capuchins having to pull handles or press levers in complex devices that the animals did not understand. They did not pull the handle more often when a partner was pulling; both novices and experienced participants kept pulling even in situations where success was impossible. Visalberghi, Quarantotti, and Tranchida concluded that there was no evidence of an appreciation of the role played by the partner. The first test with evidence of cooperation in capuchins happened when de Waal and Brosnan adopted Crawford's pulling paradigm. Two captive monkeys were situated in adjacent sections of a test chamber, with a mesh partition between them. In front of them was an apparatus consisting of a counter-weighted tray with two pull bars and two food cups. Each monkey had access to only one bar and one food cup, but could see both, and only one cup was filled with food. The tray was too heavy for one monkey to pull it in, with weights established over trials lasting three years. Only when they worked together and both pulled could they move the tray, enabling one of them to grab the food. Trained monkeys were much more successful if they both obtained rewards after pulling than if only one of them received rewards. The pull rate dropped significantly when monkeys were alone at the apparatus, suggesting an understanding of the need for a partner. In later tests, researchers replaced the mesh partition with an opaque barrier with a small hole, so that the monkeys could see the other one was there but not their actions. This dramatically reduced success in cooperation.
De Waal and Berger used the cooperative pulling paradigm to investigate animal economics. They compared the behavior when both transparent bowls were loaded with food to when just one was loaded, and with a solo task where the partner was only an observer and unable to help. They found that captive capuchin monkeys were willing to pull even if their bowl was empty and it was uncertain if their partner would share food. In 90% of cases the owner of the food did indeed share the food. Food was shared more often if the partner actually worked for it than just being an observer. Brosnan, Freeman, and de Waal tested captive capuchin monkeys on a bar-pulling apparatus with unequal rewards. Contrary to their expectations, rewards did not have to be distributed equally to achieve success. What mattered was the behavior in an unequal situation: pairs that tended to alternate which monkey received the higher-value food were more than twice as successful in obtaining rewards than pairs in which one monkey dominated the higher-value food.
==== Tamarins ====
Cottontop tamarins (Saguinus oedipus) are small monkeys who take care of their young cooperatively in the wild. Cronin, Kurian, and Snowdon tested eight captive cottontop tamarins in a series of cooperative pulling experiments. Two monkeys were put on opposite sides of a transparent apparatus containing food. Only if both monkeys pulled a handle on their side of the apparatus towards themselves at the same time would food drop down for them to obtain. The tamarins were first trained, through shaping techniques, to use the handles successfully by themselves. In the joint pulling test pairs were successful in 96% of trials. The researchers then ran a second study in which a tamarin was tested alone. The results showed that tamarins pulled the handles at a lower rate when alone with the apparatus than when in the presence of a partner. Cronin, Kurian, and Snowdon concluded from this that cottontop tamarins have a good understanding of cooperation. They suggest that cottontop tamarins have developed cooperative behavior as a cognitive adaptation.
==== Macaques ====