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Wiki Edit
https://en.wikipedia.org/wiki/Reciprocal_altruism#cite_note-15 this is the link to the article I edited. I added the Nest defending section shown below:

Nest Protecting
In red-winged black bird males help defend neighbor's nests. There are many theories as to why males behave this way. One is that males only defend other nests which contain their extra-pair offspring. Extra-pair offspring is juveniles which may contain some of the male bird's DNA. Another is the tit-for-tat strategy of reciprocal altruism. A third theory is, males help only other closely related males. A study done by The Department of Fisheries and Wildlife provided evidence that males used a tit-for-tat strategy. The Department of Fisheries and Wildlife tested many different nests by placing stuffed crows by nests, and then observing behavior of neighboring males. The behaviors they looked for included the number of calls, dives, and strikes. After analyzing the results, there was not significance evidence for kin selection; the presence of extra-pair offspring did not affect the probability of help in nest defense. However, males reduced the amount of defense given to neighbors when neighbor males reduced defense for their nests. This demonstrates a tit-for-tat strategy, where animals help those who previously helped them. This strategy is one type of reciprocal altruism. [15]

FINAL PAPER
The evolution of altruism was first explained by the scientist, Hamilton. Hamilton suggested that altruism evolved among relatives due to inclusive fitness (Fletcher and Zwick 2006). Inclusive fitness is an individual’s direct fitness, from producing its own offspring, as well as its indirect fitness, the number of offspring produced by its relatives. Hamilton uses the equation: rb > c, where r = relatedness, b = benefit of recipient, and c = cost to altruist, to explain why an animal might behave altruistically. Hamilton’s idea was individuals that followed this rule and behaved altruistically, when the indirect fitness benefit outweighed the cost, would pass on more of their genes, including their cooperation genes (Fletcher and Zwick 2006). The idea of an individual helping another based on their relatedness is referred to as kin-selection (Fletcher and Zwick 2006). According to Hamilton’s rule, an individual will not help if the indirect fitness benefit does not outweigh the cost (Fletcher and Zwick 2006). However, this does not explain why individuals sometimes help unrelated individuals. When an organism helps an unrelated individual it is called reciprocal altruism. Evolutionary biologists have spent much time researching reciprocal altruism in order to better understand it. According to researchers at Portland State University, there needs to be phenotypic differentiation between individuals with cooperative or altruistic genes and those without these genes in order for reciprocal altruism to evolve (Fletcher and Doebeli 2009). This phenotypic variation allows selection to act on individuals. One of the most popular models used to explain the reasoning behind reciprocal altruism is called the Prisoner’s Dilemma (Fletcher and Zwick 2006).

The Prisoner’s Dilemma is commonly used to attempt to understand reciprocal altruism. Many forms of the model exist, but one of the simplest ones consists of two participants. Each participant can choose to either cooperate or defect (Fletcher and Zwick 2006). If both cooperate they will each get the highest possible benefit. However, in mixed situations the defector gets a higher benefit than the cooperator (Fletcher and Zwick 2006). Since an individual is unaware if the other will cooperate or defect, it has to decide if it wants to take the risk of cooperating. The most successful strategy, found by Axelrod, is called Tit-for-Tat or TFT (Fletcher and Zwick 2006). When using the TFT strategy, an individual will always cooperate in the first round, and then in the following rounds it will repeat whatever the other individual did (Fletcher and Zwick 2006). In his article, Robert Trivers uses a different model to demonstrate reciprocal altruism. He uses the drowning man scenario (Trivers 1971). In this scenario, man 1 is drowning and man 2 deciding whether to save him or not. The risk of dying for man 1 is 50%, if man 2 does not try to save man 1. If the man 2 tries to save man 1, the risk of both men dying is significantly less. However, if the man 2 does nothing he will live for sure. Based on this one time scenario man 2 should do nothing and save himself, but if man 2 thought he could be the one drowning next time he should help. By helping man 2 hopes that when the situation is reversed man 1 will save him (Trivers 1971). If both men are altruists, they have a greater overall chance to survive, and a greater probability for passing on their altruistic genes. Therefore, altruists are selected for (Trivers 1971). Cheaters, individuals who do not reciprocate altruistic acts, will be selected against if other individuals in the population stop altruistic behavior towards cheaters. This is because the cost of losing these altruistic acts outweighs the benefits of cheating (Trivers 1971). This model demonstrates how Tit-for-Tat may evolve in a population. Animals often demonstrate this Tit-for-Tat strategy in nature. One experiment, performed at The University of Illinois, tested altruism in vampire bats. Vampire bats feed only on blood and starve after 70 hours with no meals. This led to food sharing among bats (Carter and Gerald 2013). The evolution of this behavior suggests that cooperation results in an overall increase of inclusive fitness. The researches at The University of Illinois tested three hypothesizes: non-kin food sharing to dominant individuals, non-kin food sharing to past donors, and food sharing to only kin (Carter and Gerald 2013). In order to test these hypothesizes; a colony of bats with mixed relatedness was used. Relatedness was determined by extracting DNA strands and performing tests using microsatellite loci to estimate the maximum-likelihood coefficient of relatedness (Carter and Gerald 2013). The researches designed the experiment to compare relatedness, past donors, receiver size and gender, and group mates as predictors for food sharing (Carter and Gerald 2013). The experiment was conducted by removing a bat from the population for 24 hours with no food, and then returning the bat to the population and observing behavior and social interactions. Food sharing was quantified by the donor licking the receiver’s mouth for at least 5 seconds (Carter and Gerald 2013). The results of this experiment were, food sharing occurred between mostly female bats, and never between adult males. However a study done by The Joint Science Department at Claremont Colleges found that food sharing and allogrooming was common among adult male bats (DeNault and Donald 1994). This suggests the previously thought strong hierarchy system of bat colonies may be inaccurate (DeNault and Donald 1994). In the experiment done at The University of Illinois, when a bat received food, the amount received was equal to 5% of its mass. The results of this study suggested that allogrooming received, relatedness, and donor sex and size are not good predictors for future food sharing. The results did suggest that past donors was the best predictor for future sharing (Carter and Gerald 1994). These results show that reciprocal altruism is present in vampire bat colonies, and that many bats use the Tit-for-Tat strategy when deciding if they will participate in food sharing. Another example of reciprocal altruism in nature is found in red-winged black bird populations. In red-winged black bird populations, males help defend neighbor’s nests. There are multiple theories as to why male birds protect others’ nests. One is that males only defend other nests which contain their extra-pair offspring. Another is the tit-for-tat strategy of reciprocal altruism. A third theory is, males help only other closely related males (Olendorf, Getty, Scribner 2004). Together The Department of Fisheries and Wildlife and researchers at Michigan State performed and experiment to find the cause of nest defending in red-winged black birds (Olendorf, Getty, Scribner 2004). The experiment was designed to test for by-product mutualism, kin-selection, and reciprocal altruism (Olendorf, Getty, Scribner 2004). They tested nest defending by placing stuffed crows by nests, and observing the behavior of neighboring males, such as number of calls, dives, and strikes (Olendorf, Getty, Scribner 2004). The results of this experiment did not suggest a significant relationship between relatedness of males and defense of neighboring nests or defense of nests containing extra-pair offspring and those without defending male’s extra-pair offspring. However, males reduced the amount of defense given to neighbors when neighbor males reduced defense for their nests (Olendorf, Getty, Scribner 2004). This strongly suggests that reciprocal altruism is responsible for nest defense cooperation in red-winged black birds. It also demonstrates the Tit-for Tat strategy just as food sharing in vampire bats, since birds who don’t reciprocate the action of nest guarding are less likely to receive help when their nest is threatened.

A third study found a new twist on the Tit-for-Tat strategy. Ecologist, Gabrielle Schino, preformed a meta-analysis on primates (Schino 2006). In primate dyads altruistic acts of allogrooming and agnostic support are exchanged between individuals. Allogrooming is the act of grooming another individual’s fur, and agnostic support is the act of helping an individual in a fight with another dyad member (Schino 2006). It has been suggested that primates groom individuals of higher rank so that in the event of a fight the higher ranking individual will support the primate which groomed it the most (Schino 2006). This would be an example of a Tit-for Tat strategy, but is slightly different because the altruistic act is done, grooming, so that a different altruistic act will be reciprocated, agnostic support. Schino specifically wanted to test if individuals who groomed the most were more likely to receive agnostic support (Schino 2006). To do this he performed a meta-analysis on 36 different studies. Only data from good studies was used in the end results. Good studies were ones that used matrix-correlations so as not to assume that dyads were independent. Bad studies did not use matrix-correlations causing data collected to show the assumption of dyad independence (Schino 2006). The results of this analysis showed a strong relationship between allogrooming and agnostic support, meaning individuals provided agnostic support to those who groomed them most (Schino 2006). There was not enough evidence to suggest that hierarchy had a significant effect on who primates decided to groom. Further studies will have to be done to test this hypothesis (Schino 2006).

Some studies have shown reciprocal altruism in human civilizations. One study, done by Michael Gurven, showed reciprocal altruism in Hiwi and Ache modern day hunter-gatherers (Gurven 2004). After studying the two groups of people, Gurven concluded that food sharing between family groups was present. Families would give food to other families so that in the future the donor family would receive food from the recipient family (Gurven 2004).

The evolution of altruism through kin selection is easy to understand. Animals have instincts which help them pass on the maximum number of genes. Therefore, helping others who have most of the same genes as an individual would present a benefit to that individual and increase its fitness. The topic of reciprocal altruism is harder to understand because helping others who are unrelated will not directly or immediately benefit an individual. Scientists have accepted the Tit-for-Tat strategy as a way to explain how reciprocal altruism could have evolved. The Tit-for-Tat strategy states that individuals behave altruistically in order to receive benefits in the future. This concept has been illustrated in multiple case studies. Vampire bats have been shown to share food with those who previously shared food with them (Carter and Gerald 2013). Also there is evidence to support that red-winged black birds help defend the nest of those that help defend their nests (Olendorf, Getty, Scribner 2004). A third example of reciprocal altruism in the animal kingdom can be seen in primates. Primates have been shown to groom others so that they will gain agnostic support in the future (Schino 2006). Reciprocal altruism has even been found in people. One study showed food sharing among Hiwi and Ache hunter-gatherer groups (Gurven 2004). These are just a few case studies of the many examples of reciprocal altruism in the animal kingdom. Evolutionary biologists have only just begun to understand reciprocal altruism. Much more research must be done in order to fully understand the evolution of altruism.

Works Cited Carter, Gerald G., and Gerald S. Wilkinson. "Food Sharing in Vampire Bats: Reciprocal Help Predicts Donations More than Relatedness or Harassment." Proceedings of the Royal Society 280.1753 (2013): n. pag. Royal Society Publishing. Royal Society Publishing, 2 Jan. 2013. Web. 14 Sept. 2014 DeNault, Lisa K., and Donald A. McFarlane. "Reciprocal Altruism between Male Vampire Bats, Desmodus rotundus." Reciprocal Altruism between Male Vampire Bats, Desmodus rotundus (1994): n. pag. The Claremont Colleges, 21 Nov. 1994. Web. 25 Oct. 2014. Fletcher, Jeffrey A., and Michael Doebeli. "A Simple and General Explanation for the Evolution of Altruism." A Simple and General Explanation for the Evolution of Altruism. Royal Society Publishing, Jan.-Feb. 2009. Web. 13 Sept. 2014. Fletcher, Jeffrey A., and Martin Zwick. "Unifying the Theories of Inclusive Fitness and Reciprocal Altruism." The American Naturalist 168.2 (2006): 252-62. 14 July 2006. Web. 14 Sept. 2014 Gurven, Michael. "Reciprocal Altruism and Food Sharing Decisions among Hiwi and Ache Hunter-gatherers." Behavioral Ecology and Sociobiology 56.4 (2004): 366-80. Springer-Verlag, 20 May 2004. Web. 25 Oct. 2014. Olendorf, Robert, Thomas Getty, and Kim Scribner. "Cooperative Nest Defence in Red–winged Blackbirds: Reciprocal Altruism, Kinship or By–product Mutualism?" Cooperative Nest Defence in Red–winged Blackbirds: Reciprocal Altruism, Kinship or By–product Mutualism?Royal Society Publishing, 22 Jan. 2004. Web. 14 Sept. 2014.

Schino, Gabriele. "Grooming and Agonistic Support: A Meta-analysis of Primate Reciprocal Altruism." Grooming and Agonistic Support: A Meta-analysis of Primate Reciprocal Altruism. Advanced Access, 3 Oct. 2006. Web. 26 Oct. 2014. Trivers, Robert L. "The Evolution of Reciprocal Altruism." The Quarterly Review of Biology 46 (1971): 35-57. Berkeley.edu. University of Chicago Press, Mar. 1971. Web. 25 Oct. 2014.

Article:

https://en.wikipedia.org/wiki/Reciprocal_altruism

Three Improvements:

In the bat example, it could be included that some experiments have shown that there is stronger correlation between previous cooperation and future food sharing, and little correlation between relatedness and food sharing. Under the Theory section, it could be included that reciprocal altruism evolved because those with altruistic genes help each other, therefore increasing their fitness and the number of altruistic genes in the next generation. An example of nest guarding, specifically in male red-winged blackbirds could also be included. — Preceding unsigned comment added by Mitchell.1071 (talk • contribs) 01:57, 2 October 2014 (UTC)

Additional Sentence: Since bats only feed on blood and will die after just 70 hours of not eating, this food sharing is a great benefit to the receiver an a great cost to the giver.