Publications

2012
Krasnow MM, Cosmides L, Pedersen EJ, Tooby J. What Are Punishment and Reputation for?. PLoS ONE. 2012;7 (9) :e45662.Abstract

Why did punishment and the use of reputation evolve in humans? According to one family of theories, they evolved to support the maintenance of cooperative group norms; according to another, they evolved to enhance personal gains from cooperation. Current behavioral data are consistent with both hypotheses (and both selection pressures could have shaped human cooperative psychology). However, these hypotheses lead to sharply divergent behavioral predictions in circumstances that have not yet been tested. Here we report results testing these rival predictions. In every test where social exchange theory and group norm maintenance theory made different predictions, subject behavior violated the predictions of group norm maintenance theory and matched those of social exchange theory. Subjects do not direct punishment toward those with reputations for norm violation per se; instead, they use reputation self-beneficially, as a cue to lower the risk that they personally will experience losses from defection. More tellingly, subjects direct their cooperative efforts preferentially towards defectors they have punished and away from those they haven’t punished; they avoid expending punitive effort on reforming defectors who only pose a risk to others. These results are not consistent with the hypothesis that the psychology of punishment evolved to uphold group norms. The circumstances in which punishment is deployed and withheld–its circuit logic–support the hypothesis that it is generated by psychological mechanisms that evolved to benefit the punisher, by allowing him to bargain for better treatment.

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2011
Delton AW, Krasnow MM, Cosmides L, Tooby J. Reply to McNally and Tanner: Generosity evolves when cooperative decisions must be made under uncertainty. Proc Natl Acad Sci U S A. 2011;108 (44) :E972. PDF
Krasnow MM, Truxaw D, Gaulin SJC, New J, Ozono H, Uono S, Ueno T, Minemoto K. Cognitive adaptations for gathering-related navigation in humans. Evolution and Human Behavior. 2011;32 :1 - 12.Abstract

Current research increasingly suggests that spatial cognition in humans is accomplished by many specialized mechanisms, each designed to solve a particular adaptive problem. A major adaptive problem for our hominin ancestors, particularly females, was the need to efficiently gather immobile foods which could vary greatly in quality, quantity, spatial location and temporal availability. We propose a cognitive model of a navigational gathering adaptation in humans and test its predictions in samples from the US and Japan. Our results are uniformly supportive: the human mind appears equipped with a navigational gathering adaptation that encodes the location of gatherable foods into spatial memory. This mechanism appears to be chronically active in women and activated under explicit motivation in men.

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Delton AW, Krasnow MM, Cosmides L, Tooby J. Evolution of direct reciprocity under uncertainty can explain human generosity in one-shot encounters. Proc Natl Acad Sci U S A. 2011;108 (32) :13335-40.Abstract

Are humans too generous? The discovery that subjects choose to incur costs to allocate benefits to others in anonymous, one-shot economic games has posed an unsolved challenge to models of economic and evolutionary rationality. Using agent-based simulations, we show that such generosity is the necessary byproduct of selection on decision systems for regulating dyadic reciprocity under conditions of uncertainty. In deciding whether to engage in dyadic reciprocity, these systems must balance (i) the costs of mistaking a one-shot interaction for a repeated interaction (hence, risking a single chance of being exploited) with (ii) the far greater costs of mistaking a repeated interaction for a one-shot interaction (thereby precluding benefits from multiple future cooperative interactions). This asymmetry builds organisms naturally selected to cooperate even when exposed to cues that they are in one-shot interactions.

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2010
Delton AW, Krasnow MM, Cosmides L, Tooby J. Evolution of fairness: Rereading the data. Science. 2010;329. PDF
2007
Krasnow MM, Truxaw D, New J, Gaulin SJC. Shopping for Explanations, Response. Science. 2007;318 (5851) :745. PDF
New J, Krasnow MM, Truxaw D, Gaulin SJC. Spatial adaptations for plant foraging: women excel and calories count. Proceedings of the Royal Society B: Biological Sciences. 2007;274 :2679 - 2684.Abstract

We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources. In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate that a simple but ecologically important shift in content can reverse this sex difference. This effect is predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for gathering-specific spatial mechanisms, some of which are sexually differentiated. The hypothesis that gathering-specific spatial adaptations exist in the human mind is further supported by our finding that spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density). This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efficient foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain specific and designed by natural selection to mesh with important regularities of the ancestral world.

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2006
Truxaw D, Krasnow MM, Woods C, German TP. Conditions Under Which Function Information Attenuates Name Extension via Shape. Psychological Science. 2006;17 :367 - 371.Abstract

ABSTRACT- Children often extend names to novel artifacts on the basis of overall shape rather than core properties (e.g., function). This bias is claimed to reflect the fact that nonrandom structure is a reliable cue to an object having a specific designed function. In this article, we show that information about an object's design (i.e., about its creator's intentions) is neither necessary nor sufficient for children to override the shape bias. Children extend names on the basis of any information specifying the artifact's function (e.g., information about design, current use, or possible use), especially when this information is made salient when candidate objects for extension are introduced. Possible mechanisms via which children come to rely less on easily observable cues (e.g., shape) and more on core properties (e.g., function) are discussed.

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