Editing Game theory (section)

=== Biology ===
{{Payoff matrix |Name=The [[Chicken (game)#Hawk-Dove|hawk-dove]] game |2L=Hawk |2R=Dove |1U=Hawk |UL=20, 20 |UR=80, 40 |1D=Dove |DL=40, 80 |DR=60, 60}}
{{main|Evolutionary game theory}}

Unlike those in economics, the payoffs for games in [[biology]] are often interpreted as corresponding to [[Fitness (biology)|fitness]]. In addition, the focus has been less on equilibria that correspond to a notion of rationality and more on ones that would be maintained by evolutionary forces. The best-known equilibrium in biology is known as the ''[[evolutionarily stable strategy]]'' (ESS), first introduced in {{harv|Maynard Smith|Price|1973}}. Although its initial motivation did not involve any of the mental requirements of the Nash equilibrium, every ESS is a Nash equilibrium.

In biology, game theory has been used as a model to understand many different phenomena. It was first used to explain the evolution (and stability) of the approximate 1:1 [[sex ratio]]s. {{harv|Fisher|1930}} suggested that the 1:1 sex ratios are a result of evolutionary forces acting on individuals who could be seen as trying to maximize their number of grandchildren.

Additionally, biologists have used evolutionary game theory and the ESS to explain the emergence of [[animal communication]].{{sfnp|Harper|Maynard Smith|2003}} The analysis of [[signaling games]] and [[Cheap talk|other communication games]] has provided insight into the evolution of communication among animals. For example, the [[mobbing behavior]] of many species, in which a large number of prey animals attack a larger predator, seems to be an example of spontaneous emergent organization. Ants have also been shown to exhibit feed-forward behavior akin to fashion (see [[Paul Ormerod]]'s ''[[Butterfly Economics]]'').

Biologists have used the [[Chicken (game)|game of chicken]] to analyze fighting behavior and territoriality.<ref>{{Cite journal |last1=Maynard Smith |first1=John |author-link=John Maynard Smith |title=The theory of games and the evolution of animal conflicts |doi=10.1016/0022-5193(74)90110-6 |journal=Journal of Theoretical Biology |volume=47 |issue=1 |pages=209–221 |year=1974 |pmid=4459582 |bibcode=1974JThBi..47..209M |url=http://www.dklevine.com/archive/refs4448.pdf }}</ref>

According to Maynard Smith, in the preface to ''Evolution and the Theory of Games'', "paradoxically, it has turned out that game theory is more readily applied to biology than to the field of economic behaviour for which it was originally designed". Evolutionary game theory has been used to explain many seemingly incongruous phenomena in nature.<ref name="stan-egt">{{cite encyclopedia |editor-link=Edward N. Zalta |editor-first=Edward N. |editor-last=Zalta |url=http://plato.stanford.edu/entries/game-evolutionary/ |title=Evolutionary Game Theory |encyclopedia=Stanford Encyclopedia of Philosophy |publisher=Stanford University |access-date=3 January 2013 |date=19 July 2009 |first=J. McKenzie |last=Alexander}}</ref>

One such phenomenon is known as [[Altruism in animals|biological altruism]]. This is a situation in which an organism appears to act in a way that benefits other organisms and is detrimental to itself. This is distinct from traditional notions of altruism because such actions are not conscious, but appear to be evolutionary adaptations to increase overall fitness. Examples can be found in species ranging from vampire bats that regurgitate blood they have obtained from a night's hunting and give it to group members who have failed to feed, to worker bees that care for the queen bee for their entire lives and never mate, to [[vervet monkey]]s that warn group members of a predator's approach, even when it endangers that individual's chance of survival.<ref name="qudzyh">{{cite encyclopedia |editor-first=Edward N. |editor-last=Zalta |url=https://plato.stanford.edu/entries/altruism-biological/ |title=Biological Altruism |encyclopedia=Stanford Encyclopedia of Philosophy |date=3 June 2003 |access-date=3 January 2013 |publisher=Stanford University |editor-link=Edward N. Zalta |first=Samir |last=Okasha}}</ref> All of these actions increase the overall fitness of a group, but occur at a cost to the individual.

Evolutionary game theory explains this altruism with the idea of [[kin selection]]. Altruists discriminate between the individuals they help and favor relatives. [[Kin selection#Hamilton's rule|Hamilton's rule]] explains the evolutionary rationale behind this selection with the equation {{Math|c < b &times; r}}, where the cost {{varserif|c}} to the altruist must be less than the benefit {{varserif|b}} to the recipient multiplied by the coefficient of relatedness {{varserif|r}}. The more closely related two organisms are causes the incidences of altruism to increase because they share many of the same alleles. This means that the altruistic individual, by ensuring that the alleles of its close relative are passed on through survival of its offspring, can forgo the option of having offspring itself because the same number of alleles are passed on. For example, helping a sibling (in diploid animals) has a coefficient of {{frac|1|2}}, because (on average) an individual shares half of the alleles in its sibling's offspring. Ensuring that enough of a sibling's offspring survive to adulthood precludes the necessity of the altruistic individual producing offspring.<ref name="qudzyh" /> The coefficient values depend heavily on the scope of the playing field; for example if the choice of whom to favor includes all genetic living things, not just all relatives, we assume the discrepancy between all humans only accounts for approximately 1% of the diversity in the playing field, a coefficient that was {{frac|1|2}} in the smaller field becomes 0.995. Similarly if it is considered that information other than that of a genetic nature (e.g. epigenetics, religion, science, etc.) persisted through time the playing field becomes larger still, and the discrepancies smaller.