What counts as human rationality: reasoning processes that embody content-independent formal theories, such as propositional logic, or reasoning processes that are well designed for solving important adaptive problems? Most theories of human reasoning have been based on content-independent formal rationality, whereas adaptive reasoning, ecological or evolutionary, has been little explored. We elaborate and test an evolutionary approach, Cosmides' social contract theory, using the Wason selection task. In the first part, we disentangle the theoretical concept of a “social contract” from that (...) of a “cheater-detection algorithm”. We demonstrate that the fact that a rule is perceived as a social contract — or a conditional permission or obligation, as Cheng and Holyoak proposed — is not sufficient to elicit Cosmides' striking results, which we replicated. The crucial issue is not semantic, but pragmatic: whether a person is cued into the perspective of a party who can be cheated. In the second part, we distinguish between social contracts with bilateral and unilateral cheating options. Perspective change in contracts with bilateral cheating options turns P & not-Q responses into not-P & Q responses. The results strongly support social contract theory, contradict availability theory, and cannot be accounted for by pragmatic reasoning schema theory, which lacks the pragmatic concepts of perspectives and cheating detection. (shrink)

Evolutionary theory predicts that humans should avoid incest because of the negative effects incest has on individual reproduction: production of defective offspring. Selection for the avoidance of close-kin mating has apparently resulted in a psychological mechanism that promotes voluntary incest avoidance. Most human societies are thought to have rules regulating incest. If incest is avoided, why are social rules constructed to regulate it? This target article suggests that incest rules do not exist primarily to regulate close-kin mating but to regulate (...) inbreeding between more distant kin and sexual relations between affinal relatives. Three evolutionary hypotheses about cousin marriage and affinal kin mating follow from this suggestion: Rules regulating mating between affinal kin are means of paternity protection. Cousin marriage is regulated because, if it occurs, it can concentrate wealth and power within families to the detriment of the powerful positions of rulers in stratified societies and the relatively equal social statuses of most men in egalitarian societies. Tests using the comparative method on a worldwide sample of 129 societies supported the three hypotheses. Two alternative anthropological hypotheses failed to be supported. (shrink)

Much clinical and ethnographic evidence suggests that humans, like many other organisms, are selected to avoid close inbreeding because of the fitness costs of inbreeding depression. The proximate mechanism of human inbreeding avoidance seems to be precultural, and to involve the interaction of genetic predispositions and environmental conditions. As first suggested by E. Westermarck, and supported by evidence from Israeli kibbutzim, Chinese sim-pua marriage, and much convergent ethnographic and clinical evidence, humans negatively imprint on intimate associates during a critical period (...) of early childhood.There is also much evidence that, like other social animals, humans do not seek to maximize outbreeding, but rather to maintain an optimal balance between outbreeding and inbreeding.Closeinbreeding reduces fitness through inbreeding depression, butsomeinbreeding brings the benefits of nepotism. For simple, stateless, horticultural societies, the optimal balance seems to be achieved by a combination of precultural inbreeding avoidance of relatives with anr≤·25 and cultural rules of preferential marriage with kin withr≥·25. Adjustment of the coefficient of inbreeding to other ecological settings seems to be largely cultural. An interactive model of “culture in nature” is presented, in which culture is seen as coevolving with genes to produce the maxiniization of individual inclusive fitness. (shrink)

"This reviewer had to be restrained from stopping people in the street to urge them to read it: They would learn something of the way science is done,...

Second, this collection of cognitive programs evolved in the Pleistocene to solve the adaptive problems regularly faced by our hunter-gatherer ancestors-...