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Nikolas Block, Graciela Alvarez, Lucas Bowe, Katie Athanson

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Many animals demonstrate what’s called reciprocity, or reciprocal altruism, which is what we’ll be discussing in our presentation, specifically the reciprocal behaviors of non-human primates such as the capuchin monkey. Like humans, many primates live in groups and need to work together in order to survive as a whole, and many individuals perform reciprocal behavior in order to increase their advantages within the group itself. For example, in groups of rhesus macaque monkeys there is a strict social order in which individuals in higher ranking social status have more access to and tolerance at drinking holes and other resources, and therefore individuals with lower social status would exhibit reciprocal grooming in order to gain more tolerance around drinking holes. (Balasubramaniam, 2017)

We are seeking to understand the evolutionary “why” behind reciprocity, and to also continue to identify the many ways that these behaviors benefit individuals, groups, and contribute to evolution and survival. There is a lot of research already done on this topic, and by continuing to explore it in the world of monkeys, we will be better able to understand the etiology of reciprocal behaviors commonly shown by humans (such as sharing money, shelter, or food), and it may also provide more evidence supporting the theory of evolution, since humans and non-human primates share many similar prosocial behaviors.

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Capuchin monkeys often live in large groups of 10 to 35. They live under a discreet hierarchy that is broken down by age and sex. A male will dominate the group and he would get first picks on the females in the group. The group serves each other by mutual grooming (allogrooming) and has calls that serve different purposes like warning about predators and forming new groups.

Capuchin monkeys are known as one of the smartest monkeys and are able to cognitively recognize different primates and recall their previous encounters. The parental capuchin monkeys teach their young how to obtain foods and use tools to gather certain kinds of foods. Capuchin monkeys in experimental studies were able to help each other out and push resources closer to other monkeys. They also understand the token system and use it to help kin and non-kin capuchin monkeys, and even use the token system with humans when entertaining. Capuchin monkeys can even go as far as understanding the donation rates and quality of their partner’s food and understand that long-term exchanges are of greater importance than short-term exchanges

(Fragaszy, 2004)

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Altruism is defined as the selfless care for the well being of others at a direct cost to oneself. Altruism will arise in animals when the act of altruism will be overall beneficial for the animal's fitness because the direct cost is not as much as the indirect benefit. A time when this indirect benefit would occur is when the one being helped is closely related to or the kin of the animal doing the altruistic act. Then by doing the altruistic act the animal may lose some of it's own reproductive success, but will increase the reproductive success of it's relatives so much so that it's overall fitness is higher than if it had not done the altruistic act. (Okasha, 2013)

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A marmoset in Serra Grande, Bahia (Brazil) resists eating bananas while it calls and waits for the remaining individuals of the group

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Reciprocity is the exchanging of things with others for benefits. This can be seen in different ways, such as allogrooming. In order for reciprocity to happen primates must meet certain parameters for reciprocity to happen. Firstly, primates must live a long life so the chances of interactions are increased, primates should also be close to each other in proximity so their amount of encounters is high, mutual dependence is necessary to increase sociality, parental care to also increase that dependence, and agonistic support to increase the need for allies. Also for reciprocity to happen we obviously need to have individual recognition between other primates, and memory of previous encounters. The memory of certain primates can indicate whether the primate is able to provide long-term reciprocity and short-term reciprocity.
(Schweinfurth & Call, 2019)

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Factors that Influence Reciprocal Cooperation in Primates:

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Factors that Influence Reciprocal Cooperation in Primates:

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Manon K Schweinfurth broke down some observations in what influenced reciprocal cooperation. He was able to pinpoint a few:

Kinship:
In primates, cooperative interactions occur among kin. However, reciprocity might become an important factor to choose the best cooperative partner among multiple relatives.

Relationship quality:
In some primates, reciprocity is only done through relatives, while in other primates like Capuchin monkeys, reciprocity is done through the whole community of monkeys.

Partner choice:
Reciprocity is a timely process. Because it takes time to give back to another primate they are susceptible to cheating (free-riding). Reciprocity might be stopped because the cheater cheats too often, or it is found that the partner will participate in punishing them until they stop showing cheating behaviors.

Cognitive mechanisms:
Different primates' brains are all developed differently. The temporal lobe has a lot to do with memory and with long delays in the ability to reciprocate, results will increase in errors especially when multiple partners have helped the primate.

(Schweinfurth & Call, 2019)

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Forms of Reciprocity and the Commonality During the Studies

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Forms of Reciprocity and the Commonality During the Studies

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(Schweinfurth & Call, 2019)

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Cooperation via reciprocal altruism can be seen in this video. The first monkey gives the rock to the second because although he does not know if the monkey who received the rock will give him food, he still does the altruistic act in hopes of benefiting from it. And once the second monkey gets to the food he displays reciprocal altruism by giving food to the monkey whom gave him the rock which is what allowed him to get the food.

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Reciprocity Specifically in Brown Capuchin Monkeys 

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Reciprocity Specifically in Brown Capuchin Monkeys 

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-Suchak & Waal, 2012 conducted a study looking to see if direct reciprocity present influenced brown capuchin monkeys' social reciprocity behavior
-Pro-social behavior is defined as motivation to do things for others with no regard to potential pay-off
(Suchak & Waal, 2012).

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To test this brown capuchin monkeys were put into 1 of the 4 conditions with different variations of the Prosocial choice test (PCT)

-PCT- is a test that forced the subject to make a decision that would be prosocial and benefit both the chooser and the non-chooser, or selfish and only benefit the chooser.

-In this experiment: monkeys were placed in 1 of 4 conditions and were taught that one token meant they would get double the apples and the other token meant they got to share with the other monkey in the pair.

(Suchak & Waal, 2012)

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In group and out group pairs were tested on each condition
-In group monkeys are defined as a monkey that the other monkey in the pair has seen frequently in the wild.
-Out group monkeys were still seen a couple times by the other monkey in the wild but were in different social groups.

-The conditions:

Unilateral- One monkey in the pair was able to make the decision of prosocial or selfish choice.

Alternating- both monkeys were able to make choices on alternating trials

Yoked control-One monkey chooses a token one trial and the next trial the researcher replicates the first choice and the partner does not choose

Two partner absence- No partner was present; this was to see if any monkeys had a preference on a certain token or not.

(Suchak & Waal, 2012)

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-For the unilateral, alternating, and yoked control conditions for all 10 trials had no difference in prosocial choices between in group and out group
-Alternating condition showed the most prosocial choices
(Suchak & Waal, 2012)

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-Brown capuchin monkeys having the most prosocial choices on the alternating conditions shows that these animals benefit from having a partner
-This might be due to attitudinal reciprocity, which means that the monkey realize that they get more apples if they share with each other on each turn, so they mirror each other's actions temporally.
(Suchak & Waal, 2012)

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This is also shown in the yoked control condition by removing the physical appearance of a partner and their partners behavior, the amount of prosocial choices decreased
-This shows that capuchin monkeys mirror their partners behavior
-As well as responding to the rewards from their choices
(Suchak & Waal, 2012)

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-To conclude, many primates shows reciprocal altruistic behavior because that is what has benefited the group overall.
-Specifically, brown capuchin monkeys (BCM) have close knit social structures and when BCM are in a lab setting with reciprocity present they tend to choose a prosocial option that benefits their partner whether they are familiar with that monkey or not.
-This shows that brown capuchin monkeys have evolved to live in a society where reciprocity behavior is favored.

-The Suchak & Waal, 2012 study looked at prosocial behavior in brown capuchin monkeys in a lab setting
-A good future direction for this topic is to conduct an observational study on reciprocity in brown capuchin monkeys in nature to see if this prosocial food sharing behavior that was discovered by Suchak & Waal, 2012 has external validity.

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Balasubramaniam, K., & Berman, C. (2017). Grooming interchange for resource tolerance: Biological markets principles within a group of free-ranging rhesus macaques. Behaviour, 154(11), 1145-1176. doi:10.1163/1568539x-00003462

Fragaszy, D. M., Visalberghi, E., & Fedigan, L. M. (2004). The Complete Capuchin: The Biology of the Genus Cebus. N.p.: Cambridge University Press.

Okasha, S. (2013, July 21). Biological altruism. https://plato.stanford.edu/entries/altruism-biological/#AltLevSel.

Schino, G., Boggiani, L., Mortelliti, A., Pinzaglia, M., & Addessi, E. (2021). Testing the two sides of Indirect reciprocity in tufted capuchin monkeys. Behavioral Processes, 182, 104290. doi:10.1016/j.beproc.2020.104290.

Schweinfurth, Manon K., and Josep Call. "Revisiting the possibility of reciprocal help in

non-human primates." Neuroscience & Biobehavioral Reviews, vol. 104, 12 June 2019, pp. 73-86, doi:https://doi.org/10.1016/j.neubiorev.2019.06.026

Suchak, M., & de Waal, F. B. (2012). Monkeys benefit from reciprocity without the cognitive burden. Proceedings of the National Academy of Sciences, 109(38), 15191–15196.        https://doi.org/10.1073/pnas.1213173109.