Editing Evolutionary psychology (section)

===Interactions with non-kin / reciprocity===
Although interactions with non-kin are generally less altruistic compared to those with kin, cooperation can be maintained with non-kin via mutually beneficial reciprocity as was proposed by Robert Trivers.<ref name=Trivers1971/> If there are repeated encounters between the same two players in an evolutionary game in which each of them can choose either to "cooperate" or "defect", then a strategy of mutual cooperation may be favored even if it pays each player, in the short term, to defect when the other cooperates. Direct reciprocity can lead to the evolution of cooperation only if the probability, w, of another encounter between the same two individuals exceeds the cost-to-benefit ratio of the altruistic act:
: w > c/b

Reciprocity can also be indirect if information about previous interactions is shared. Reputation allows evolution of cooperation by indirect reciprocity. Natural selection favors strategies that base the decision to help on the reputation of the recipient: studies show that people who are more helpful are more likely to receive help. The calculations of indirect reciprocity are complicated and only a tiny fraction of this universe has been uncovered, but again a simple rule has emerged.<ref>{{cite journal |pmid=9634232 |year=1998 |last1=Nowak |first1=MA |last2=Sigmund |first2=K |title=Evolution of indirect reciprocity by image scoring |volume=393 |issue=6685 |pages=573–77 |doi=10.1038/31225 |journal=Nature |author-link1=Martin Nowak |author-link2=Karl Sigmund |bibcode=1998Natur.393..573N |s2cid=4395576 }}</ref> Indirect reciprocity can only promote cooperation if the probability, q, of knowing someone's reputation exceeds the cost-to-benefit ratio of the altruistic act:
: q > c/b

One important problem with this explanation is that individuals may be able to evolve the capacity to obscure their reputation, reducing the probability, q, that it will be known.<ref>{{cite journal |doi=10.1038/nature04201 |title=Human cooperation: Second-order free-riding problem solved? |last1=Fowler |first1=James H. |journal=Nature |volume=437 |issue=7058 |pages=E8; discussion E8–9 |author-link1=James H. Fowler|date=22 September 2005 |pmid=16177738|bibcode=2005Natur.437E...8F |s2cid=4425399 |doi-access=free }}</ref>

Trivers argues that friendship and various social emotions evolved in order to manage reciprocity.<ref name=Gaulin-Steven-J-C-2003-pp.323-52>Gaulin, Steven J. C. and Donald H. McBurney. Evolutionary Psychology. Prentice Hall. 2003. {{ISBN|978-0-13-111529-3}}, Chapter 14, pp. 323–52.</ref> Liking and disliking, he says, evolved to help present-day humans' ancestors form coalitions with others who reciprocated and to exclude those who did not reciprocate.<ref name=Gaulin-Steven-J-C-2003-pp.323-52/> Moral indignation may have evolved to prevent one's altruism from being exploited by cheaters, and gratitude may have motivated present-day humans' ancestors to reciprocate appropriately after benefiting from others' altruism.<ref name=Gaulin-Steven-J-C-2003-pp.323-52/> Likewise, present-day humans feel guilty when they fail to reciprocate.<ref name=Gaulin-Steven-J-C-2003-pp.323-52/> These social motivations match what evolutionary psychologists expect to see in adaptations that evolved to maximize the benefits and minimize the drawbacks of reciprocity.<ref name=Gaulin-Steven-J-C-2003-pp.323-52/>

Evolutionary psychologists say that humans have psychological adaptations that evolved specifically to help us identify nonreciprocators, commonly referred to as "cheaters."<ref name=Gaulin-Steven-J-C-2003-pp.323-52/> In 1993, Robert Frank and his associates found that participants in a prisoner's dilemma scenario were often able to predict whether their partners would "cheat", based on a half-hour of unstructured social interaction.<ref name=Gaulin-Steven-J-C-2003-pp.323-52/> In a 1996 experiment, for example, [[Linda Mealey]] and her colleagues found that people were better at remembering the faces of people when those faces were associated with stories about those individuals cheating (such as embezzling money from a church).<ref name=Gaulin-Steven-J-C-2003-pp.323-52/>