People willingly confer large benefits on strangers at small cost to themselves, because it may start a mutually beneficial long-term relationship.

The claim has two parts: (a) people commonly and willingly confer large benefits on strangers at small cost to themselves, and (b) the reason is the chance of starting a mutually beneficial long-term relationship, consistent with game-theoretic 'nice' strategies. True: empirical and theoretical literature as of 2012 supports both the behaviour and the reciprocity-based explanation as established. Mostly true: the behaviour is well documented and reciprocity is a leading, supported explanation, but the claim slightly overstates certainty. Mixed: the behaviour is supported but the causal explanation is substantially contested, with comparable support for rival explanations such as strong reciprocity or group-selected altruism, or vice versa. Mostly false: the behaviour is real but the causal explanation is unproven or contradicted, or the behaviour is overgeneralised. False: the evidence shows that people do not generally confer such benefits on strangers.

Set before the research began.

1. E1 How is human cooperation different? PMC (review article, Philosophical Transactions/Biology Letters-style review by Melis and Semmann authors) · 12 September 2010

   “Cooperative behaviour is even found between complete strangers who are not likely to meet again in the future.”

2. E2 Five rules for the evolution of cooperation PMC (Nowak, Science-style review) · 8 December 2006

   “We help strangers who are in need. We donate to charities that do not donate to us.”

3. E3 Strong reciprocity, human cooperation, and the enforcement of social norms - Human Nature Springer / Human Nature · 5 March 2002

   “Strong reciprocity cannot be rationalized as an adaptive trait by the leading evolutionary theories of human cooperation (in other words, kin selection, reciprocal altruism, indirect reciprocity, and costly signaling theory).”

4. E4 How is human cooperation different? PMC (review article by other researchers) · 12 September 2010

   “Cooperation between unrelated individuals can evolve if both actor and receiver obtain immediate direct benefits from the interaction, or if individuals, who invest to help others, obtain a future benefit greater than the initial investment, for example via reciprocation (Trivers 1971).”

E1 and E2, both published before 2012, document that people help and cooperate with strangers, which supports the behavioural part of the claim. E4 notes that reciprocation is a recognised mechanism by which helping unrelated individuals can evolve. However, E3 argues that strong reciprocity cannot be explained by reciprocal altruism or the other leading theories, and E1 notes cooperation occurs even with strangers unlikely to meet again. Together these indicate that, as of 2012, the reciprocity-based causal explanation was recognised [E4] but also faced at least one rival account, strong reciprocity [E3].