Cooperation (often written as co-operation or, extremely rarely and archaically except in New Yorker magazine, coöperation) is the process of groups of organisms working or acting together for their common/mutual benefit, as opposed to working in competition for selfish benefit. Many animal and plant species cooperate both with other members of their own species and with members of other species (symbiosis or mutualism).
Language allows humans to cooperate on a very large scale. Certain studies have shown that fairness affects human cooperation; individuals are willing to punish at their own cost (altruistic punishment) if they believe that they are being treated unfairly. Sanfey, et al. conducted an experiment where 19 individuals were scanned using MRI while playing an Ultimatum Game in the role of the responder. They were receiving offers from other human partners and from a computer partner. Remarkably, responders refused unfair offers from human partners at a significantly higher rate than those by a computer partner. The experiment also showed that altruistic punishment is associated with negative emotions that are being generated in unfair situations by the anterior insula of the brain.
It has been observed that image scoring promotes cooperative behavior in situations where direct reciprocity is unlikely. In situations where reputation and status are involved, humans tend to cooperate more.
Cooperation exists not only in humans but in animals as well. This behavior appears, however, to occur mostly between relatives. Spending time and resources assisting a related individual may at first seem destructive to the organism’s chances of survival but is actually beneficial over the long-term. Since relatives share part of their genetic make-up, enhancing each other’s chances of survival may actually increase the likelihood that the helper’s genetic traits will be passed on to future generations.
Some researchers assert that cooperation is more complex than this. They maintain that helpers may receive more direct, and less indirect, gains from assisting others than is commonly reported. Furthermore, they insist that cooperation may not solely be an interaction between two individuals but may be part of the broader goal of unifying populations.
One specific form of cooperation in animals is kin selection, which can be defined as animals helping to rear a relative’s offspring in order to enhance their own fitness.
Different theories explaining kin selection have been proposed, including the "pay-to-stay" and "territory inheritance" hypotheses. The "pay-to-stay" theory suggests that individuals help others rear offspring in order to return the favor of the breeders allowing them to live on their land. The "territory inheritance" theory contends that individuals help in order to have improved access to breeding areas once the breeders depart. These two hypotheses both appear to be valid, at least in cichlid fish.
Studies conducted on red wolves support previous researchers'  contention that helpers obtain both immediate and long-term gains from cooperative breeding. Researchers evaluated the consequences of red wolves’ decisions to stay with their packs for extended periods of time after birth. It was found that this "delayed dispersal," while it involved helping other wolves rear their offspring, extended male wolves’ life spans. These findings suggest that kin selection may not only benefit an individual in the long-term in terms of increased fitness but in the short-term as well through enhanced chance of survival 
Some research even suggests that certain species provide more help to the individuals with which they are more closely related. This phenomenon is known as kin discrimination. In their meta-analysis, researchers compiled data on kin selection as mediated by genetic relatedness in 18 species, including the Western bluebird, Pied kingfisher, Australian magpie, and Dwarf Mongoose. They found that different species exhibited varying degrees of kin discrimination, with the largest frequencies occurring among those who have the most to gain from cooperative interactions.
One reason may be that if the prisoner's dilemma situation is repeated (the iterated prisoner's dilemma), it allows non-cooperation to be punished more, and cooperation to be rewarded more, than the single-shot version of the problem would suggest. It has been suggested that this is one reason for the evolution of complex emotions in higher life forms, who, at least as infants, and usually thereafter, cannot survive without cooperating – although with maturation they gain much more choice about the kinds of cooperation they wish to have.
In any case, two more recent games, the Ultimatum Game and the Dictator Game, showed that different context-related experimentations may lead to completely different results. In particular this is shown in the dictator's game, in which there are two human agents, one of which, "the ruler", is asked to decide the amount of wealth -usually in money-, between 100% and 0%, he/she is going to keep for him/herself and the one he/she is going to leave to the other human agent, which, in this game, is completely passive. Even if a "rational" economic behaviour would lead to keep the whole amount of good, it hasn't happened in experimentations, where human agents tend to share a variable amount of their goods anyway. These results were also considered a strong evidence of the absence of supposed "rational actors" in economy, especially from a neuroeconomics perspective.
- Cooperativeness (personality trait)
- Dunbar's number
- Game theory
- Management cybernetics
- Doll, Jen. "We Resist Further Cooperation on 'Coöperation'". The Wire. Retrieved 11 August 2014.
- Kohn, Alfie (1992). No Contest: The Case Against Competition. Houghton Mifflin Harcourt. p. 19. ISBN 9780395631256.
- Fehr, Ernst. "Altruistic punishment in humans" (PDF). Macmillan Magazines Ltd. Retrieved 20 July 2011.
- Sanfey, Alan G.; et al. "The Neural Basis of Economic Decision-Making in the Ultimatum Game" (PDF). Science. Retrieved 20 July 2011.
- Wedekind, Claus. "Cooperation Through Image Scoring in Humans". Science. Retrieved 20 July 2011.
- Hamilton, W.D. (1964). The Genetical Evolution of Social Behaviour I. Journal of Theoretical Biology, 7, 1-16.
- Clutton-Brock, T. (2002). Breeding together: Kin selection and mutualism in cooperative vertebrates. Science, 296(5565), 69-72. doi:10.1126/science.296.5565.69
- Balshine-Earn, S., Neat, F.C., Reid, H., & Taborsky, M. (1998). Paying to stay or paying to breed? Field evidence for direct benefits of helping behavior in a cooperatively breeding fish. Behavioral Ecology, 9 (5), 432-438.
- Sparkman, A. M., Adams, J. R., Steury, T. D., Waits, L. P., & Murray, D. L. (2011). Direct fitness benefits of delayed dispersal in the cooperatively breeding red wolf (Canis rufus). Behavioral Ecology, 22(1), 199-205. doi:10.1093/beheco/arq194
- Griffin, A. S., & West, S. A. (2003). Kin Discrimination and the Benefit of Helping in Cooperatively Breeding Vertebrates. Science, 302(5645), 634-636. doi:10.1126/science.1089402
- van den Assem, van Dolder, and Thaler (2012). "Split or Steal? Cooperative Behavior when the Stakes are Large". SSRN 1592456.
- Olsen, Harrington, and Siegelmann (2010). "Conspecific Emotional Cooperation Biases Population Dynamics: A Cellular Automata Approach".
- Harrington, Olsen, and Siegelmann (2011). "Communicated Somatic Markers Benefit the Individual and the Species".
- Herbert Gintis, Samuel Bowles, A Cooperative Species: Human Reciprocity and Its Evolution, Princeton University Press, 2011, ISBN 0-691-15125-3 (Reviewed in The Montreal Review)
- Tom R. Tyler, "Why People Cooperate: The Role of Social Motivations", Princeton University Press, 2011, ISBN 9781400836666
- Michael Tomasello, (2009), Why We Cooperate. MIT Press. ISBN 978-0-262-01359-8 (Reviewed in The Montreal Review)
- Raimo Tuomela, "Cooperation, a philosophic study", Philosophical Studies Series, Vol. 82 Kluwer Academic Publishers, 2000, ISBN 978-94-015-9594-0
- Robert Axelrod, The Complexity of Cooperation, Princeton Paperbacks, ISBN 0-691-01567-8
- Robert Axelrod, The Evolution of Cooperation, Basic Books, ISBN 0-465-02121-2
- Richard Dawkins (1990), The Selfish Gene, second edition – includes two chapters about the evolution of cooperation, ISBN 0-19-286092-5
- Herbert Gintis, Samuel Bowles, Robert T. Boyd, Ernst Fehr (eds.), Moral Sentiments and Material Interests: The Foundations of Cooperation in Economic Life (Economic Learning and Social Evolution). MIT 2005
- John McMurtry, "How Competition Goes Wrong." Journal of Applied Philosophy, 8(2): 200–210, 1991.
- Dennis Rivers, NewConversations.net, The Seven Challenges: A Workbook and Reader About Communicating More Cooperatively, fourth edition, 2005 – treats cooperation as a set of skills that can be improved.
- M.J. van den Assem, D. van Dolder and R.H. Thaler (2010). "Split or Steal? Cooperative Behavior When the Stakes are Large"
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- An Operation of Cooperation, A book about cooperation and the benefits of this path, as opposed to working alone.
- Rheingold.com, The Cooperation Project: Objectives, Accomplishments, and Proposals. Howard Rheingold's project with Institute for the Future.
- Etra.cc, Cooperation platform for transport research (scientific)
- Imprology.com, The Far Games, a list of games using theatrical improvisation to encourage collaboration and distributed leadership