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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cooperative pulling paradigm | 4/10 | https://en.wikipedia.org/wiki/Cooperative_pulling_paradigm | reference | science, encyclopedia | 2026-05-05T09:49:48.882099+00:00 | kb-cron |
Similar mixed results, not matching the cooperative abilities observed in chimpanzees in the wild, were obtained in later studies by other researchers using a variety of experimental set-ups, including the loose-string task pioneered by Hirata. Povinelli and O'Neill, for example, found that trained chimpanzees were unable to teach naive chimpanzees to cooperate on a Crawford-like box-pulling task. The naive animals did not imitate the experts. Chalmeau and Gallo found only two chimpanzees consistently cooperating in their handle-pulling task, and this involved one ape holding his own handle and waiting for the other to pull his. They concluded that social factors and not limited cognitive abilities were the reason for lack of widespread success, as they observed dominant chimpanzees controlling the apparatus and preventing others from interacting. Melis, Hare, and Tomasello set up an experiment to control for such social factors. In a loose-string cooperative task without training they compared the ability of pairs of captive chimpanzees who in a non-cooperative setting were willing to share food with each other to pairs who were less inclined to do so. The results showed that food sharing was a good predictor for success in the cooperative pulling task. Melis, Hare, and Tomasello concluded that mixed results in the past could at least partially be explained by a failure to control for such social constraints. In a follow-up study with semi–free-ranging chimpanzees, again using the loose-string task, the researchers introduced the delay task, in which subjects were tested in their ability to wait for the partner. After mastering this task, they participated in a new task designed to measure their ability to recruit the partner. They found that the apes only recruited a partner (by unlocking a door) if the task required cooperation. When given the choice between partners, the apes chose the more effective one, based on their experience with each of them previously. Suchak, Eppley, Campbell, Feldman, Quarles, and de Waal argued that even when experiments take social relationships into account, the results still do not match the cooperation capabilities observed in the wild. They set out to increase the ecological validity of their experiments by placing a handle-pulling apparatus in an open-group setting, allowing the captive chimpanzees themselves to choose to interact with it or not, and with whom. They also refrained from any training, offered as little human intervention as possible, and extended the duration to much longer than any test had ever done, to 47 days of 1 hour tests. The chimpanzees first discovered that cooperation could lead to success, but as more individuals became aware of this new way to obtain food, competition increased, taking the form of dominant apes displacing others, monopolizing the apparatus, and freeloading: taking the food others worked for. This competition led to fewer successful cooperative acts. The group did manage to restore and increase levels of cooperative behavior by various enforcement techniques: dominant individuals were unable to recruit partners and abandoned the apparatus, displacement was met with aggressive protest, and freeloaders were punished by third-party arbiters. When the researchers repeated this experiment with a brand new group of chimpanzees who not yet had established a social hierarchy, they again found that cooperation overcame competition in the long run. In a later study with a mix of novices and experts, Suchak, Watzek, Quarles, and de Waal found that novices learned rapidly in the presence of experts, although likely with limited understanding of the task. Greenberg, Hamann, Warneken, and Tomasello used a modified apparatus that required two captive chimpanzees to pull, but delivered food to one ape first. They found that in many trials the apes who already had received a reward from joint effort kept pulling to help their partner obtain their food. These partners did not need to gesture to solicit help, suggesting there was an understanding of what was wanted and needed.
==== Bonobos ====
Bonobos (Pan paniscus) are social animals that live in less hierarchical structures than chimpanzees. Hare, Melis, Woods, Hastings, and Wrangham set out to compare cooperation in chimpanzees and bonobos. They first ran a cofeeding experiment for each species. Pairs of bonobos were given two food dishes. In some trials both dishes had sliced fruit; in some one dish was empty and the other had sliced fruit; and in some one dish was empty and the other contained just two slices of fruit. The same set-up was then used for pairs of chimpanzees. When both dishes had food, there was no difference in behavior between bonobos and chimpanzees. But when only one dish contained food, bonobos were more than twice as likely to share food than chimpanzees. Bonobos were more tolerant of each other than chimpanzees. The researchers then ran a loose-string cooperation task with both dishes filled with sharable food. The results showed similar success rates for bonobos and chimpanzees, 69% of chimpanzee pairs and 50% of bonobo pairs spontaneously solving the task at least once within the six-trial test session. In a third experiment, a year later, the same cooperation task was administered but now with different food distributions. The bonobos outperformed the chimpanzees in the condition where one dish only had food and the food was clumped making it easier to monopolize the food reward. Bonobos cooperated more often in this condition. On average a single chimpanzee partner monopolized food rewards more often than a single bonobo did. In the condition where both dishes were filled with food, chimpanzees and bonobos performed similarly, as they had done the year before. The researchers concluded that the differences in performance between species were not due to differences in age, relationships, or experience. It was the bonobos' higher social tolerance level that enabled them to outperform their relatives.
==== Orangutans ====