Robert Kurzban

Evolutionary origins of stigmatization: the functions of social exclusion.

A reconceptualization of stigma is presented that changes the emphasis from the devaluation of an individuals identity to the process by which individuals who satisfy certain criteria come to be excluded from various kinds of social interactions. The authors propose that phenomena currently placed under the general rubric of stigma involve a set of distinct psychological systems designed by natural selection to solve specific problems associated with sociality. In particular, the authors suggest that human beings possess cognitive adaptations designed to cause them to avoid poor social exchange partners, join cooperative groups (for purposes of between-group competition and exploitation), and avoid contact with those who are differentially likely to carry communicable pathogens. The evolutionary view contributes to the current conceptualization of stigma by providing an account of the ultimate function of stigmatization and helping to explain its consensual nature.

Can race be erased? Coalitional computation and social categorization

Previous studies have established that people encode the race of each individual they encounter, and do so via computational processes that appear to be both automatic and mandatory. If true, this conclusion would be important, because categorizing others by their race is a precondition for treating them differently according to race. Here we report experiments, using unobtrusive measures, showing that categorizing individuals by race is not inevitable, and supporting an alternative hypothesis: that encoding by race is instead a reversible byproduct of cognitive machinery that evolved to detect coalitional alliances. The results show that subjects encode coalitional affiliations as a normal part of person representation. More importantly, when cues of coalitional affiliation no longer track or correspond to race, subjects markedly reduce the extent to which they categorize others by race, and indeed may cease doing so entirely. Despite a lifetimes experience of race as a predictor of social alliance, less than 4 min of exposure to an alternate social world was enough to deflate the tendency to categorize by race. These results suggest that racism may be a volatile and eradicable construct that persists only so long as it is actively maintained through being linked to parallel systems of social alliance.

Modularity in Cognition: Framing the Debate

Modularity has been the subject of intense debate in the cognitive sciences for more than 2 decades. In some cases, misunderstandings have impeded conceptual progress. Here the authors identify arguments about modularity that either have been abandoned or were never held by proponents of modular views of the mind. The authors review arguments that purport to undermine modularity, with particular attention on cognitive architecture, development, genetics, and evolution. The authors propose that modularity, cleanly defined, provides a useful framework for directing research and resolving debates about individual cognitive systems and the nature of human evolved cognition. Modularity is a fundamental property of living things at every level of organization; it might prove indispensable for understanding the structure of the mind as well.

An opportunity cost model of subjective effort and task performance.

Why does performing certain tasks cause the aversive experience of mental effort and concomitant deterioration in task performance? One explanation posits a physical resource that is depleted over time. We propose an alternative explanation that centers on mental representations of the costs and benefits associated with task performance. Specifically, certain computational mechanisms, especially those associated with executive function, can be deployed for only a limited number of simultaneous tasks at any given moment. Consequently, the deployment of these computational mechanisms carries an opportunity cost--that is, the next-best use to which these systems might be put. We argue that the phenomenology of effort can be understood as the felt output of these cost/benefit computations. In turn, the subjective experience of effort motivates reduced deployment of these computational mechanisms in the service of the present task. These opportunity cost representations, then, together with other cost/benefit calculations, determine effort expended and, everything else equal, result in performance reductions. In making our case for this position, we review alternative explanations for both the phenomenology of effort associated with these tasks and for performance reductions over time. Likewise, we review the broad range of relevant empirical results from across sub-disciplines, especially psychology and neuroscience. We hope that our proposal will help to build links among the diverse fields that have been addressing similar questions from different perspectives, and we emphasize ways in which alternative models might be empirically distinguished.

Perceptions of race

UNTIL RECENTLY, EXPERIMENTS ON PERSON PERCEPTION HAD LED TO TWO UNWELCOME CONCLUSIONS: (1) people encode the race of each individual they encounter, and (2) race encoding is caused by computational mechanisms whose operation is automatic and mandatory. Evolutionary analyses rule out the hypothesis that the brain mechanisms that cause race encoding evolved for that purpose. Consequently, race encoding must be a byproduct of mechanisms that evolved for some alternative function. But which one? Race is not encoded as a byproduct of domain-general perceptual processes. Two families of byproduct hypotheses remain: one invokes inferential machinery designed for tracking coalitional alliances, the other machinery designed for reasoning about natural kinds. Recent experiments show that manipulating coalitional variables can dramatically decrease the extent to which race is noticed and remembered.

Disgust: Evolved Function and Structure

Interest in and research on disgust has surged over the past few decades. The field, however, still lacks a coherent theoretical framework for understanding the evolved function or functions of disgust. Here we present such a framework, emphasizing 2 levels of analysis: that of evolved function and that of information processing. Although there is widespread agreement that disgust evolved to motivate the avoidance of contact with disease-causing organisms, there is no consensus about the functions disgust serves when evoked by acts unrelated to pathogen avoidance. Here we suggest that in addition to motivating pathogen avoidance, disgust evolved to regulate decisions in the domains of mate choice and morality. For each proposed evolved function, we posit distinct information processing systems that integrate function-relevant information and account for the trade-offs required of each disgust system. By refocusing the discussion of disgust on computational mechanisms, we recast prior theorizing on disgust into a framework that can generate new lines of empirical and theoretical inquiry.

The Neurobiology of Trust

Abstract: This is the first report that endogenous oxytocin in humans is related to social behaviors, which is consistent with a large animal literature. Subjects are put into a social dilemma in which absent communication, cooperative behavior can benefit both parties randomly assigned to a dyad. The dilemma arises because one participant must make a monetary sacrifice to signal the degree of trust in the other before the others behavioral response is known. We show that receipt of a signal of trust is associated with a higher level of peripheral oxytocin than that in subjects receiving a random monetary transfer of the same average amount. Oxytocin levels were also related to trustworthy behavior (sharing a greater proportion of the monetary gains). We conclude that oxytocin may be part of the human physiology that motivates cooperation.

Cognitive systems for revenge and forgiveness

Minimizing the costs that others impose upon oneself and upon those in whom one has a fitness stake, such as kin and allies, is a key adaptive problem for many organisms. Our ancestors regularly faced such adaptive problems (including homicide, bodily harm, theft, mate poaching, cuckoldry, reputational damage, sexual aggression, and the infliction of these costs on one’s offspring, mates, coalition partners, or friends). One solution to this problem is to impose retaliatory costs on an aggressor so that the aggressor and other observers will lower their estimates of the net benefits to be gained from exploiting the retaliator in the future. We posit that humans have an evolved cognitive system that implements this strategy – deterrence – which we conceptualize as a revenge system. The revenge system produces a second adaptive problem: losing downstream gains from the individual on whom retaliatory costs have been imposed. We posit, consequently, a subsidiary computational system designed to restore particular relationships after cost-imposing interactions by inhibiting revenge and motivating behaviors that signal benevolence for the harmdoer. The operation of these systems depends on estimating the risk of future exploitation by the harmdoer and the expected future value of the relationship with the harmdoer. We review empirical evidence regarding the operation of these systems, discuss the causes of cultural and individual differences in their outputs, and sketch their computational architecture.

Revisiting Kindness and Confusion in Public Goods Experiments

There has been substantial recent interest in determining why there is cooperation in public goods experiments even in environments that provide all subjects with the incentive to free ride (see e.g., John O. Ledyard, 1995). Theories used to explain such cooperation generally posit either that subjects are “confused” in the sense that they make errors or do not understand the game’s incentives, or that subjects contribute due to social factors such as altruism and reciprocity. Although several authors have pointed out the importance of distinguishing between these alternatives, the roles that confusion and social motives play in determining public contributions remain poorly understood. This paper provides new evidence on the way that confusion and social motives determine contributions in public goods games by reporting data from experiments that use a new design with the Voluntary Contribution Mechanism (VCM). Two important and often replicated findings in the experimental public goods literature are (1) that subjects’ public contributions are much greater than predicted by standard economic theories of free-riding and (2) that these contributions decay over the course of multiple-round games (see e.g., Douglas D. Davis and Charles A. Holt, 1993). Models that employ social factors to explain cooperation and its decay usually assume that subjects are motivated by altruism, reciprocity, or fairness (see e.g., Andreoni, 1990; Rachel T. A. Croson, 1998; Anna Gunthorsdottir et al., 2001). It has been argued, for instance, that subjects make contributions in order to elicit like contributions from reciprocators in subsequent rounds and that decay in public contributions might result from “frustrated attempts at kindness” (Andreoni, 1995 p. 892). Specifically, because there is generally heterogeneity in the willingness to contribute to the public good, initially cooperative players will likely reduce their public contributions after being grouped with relatively low contributors. In contrast, confusion theories postulate that players make public contributions either in error or because they do not understand how to pursue their self-interest. These theories argue that high initial contributions decay primarily because subjects gradually come to understand the game’s incentives. Recently, Andreoni (1995) conducted an interesting series of experiments in the first and, to our knowledge, only effort to discriminate between these competing theories of cooperative play. He provides two reasons that doing this is important. The first is that knowing the relative importance of confusion and social motives in generating cooperative decay can provide a useful guide to future research. While Andreoni argues that such knowledge could be used to inform research on learning models, note also that to the extent confusion is found to be important, shedding light on the way different sorts of instructions affect confusion could help to improve pedagogics. A second compelling reason Andreoni gives is that the outcomes of experiments designed to test theories of social giving are difficult to interpret if confusion is a primary source of cooperation. * Houser: Department of Economics and Economic Science Laboratory, University of Arizona, Tucson, AZ 85721; Kurzban: Economic Science Laboratory, University of Arizona, Tucson, AZ 85721. We thank Mark Isaac, Kevin McCabe, David Porter, Vernon Smith, Bart Wilson, seminar participants at the University of Arizona, and two anonymous referees for valuable comments on this research. The authors gratefully acknowledge the research support of fellowships from the International Foundation for Research in Experimental Economics. This research was supported by Russell Sage Foundation Grant No. 98-00-01. The authors are responsible for any errors. 1 See, for example, James Andreoni (1995), Martin Sefton and Richard Steinberg (1996), and Thomas R. Palfrey and Jeffrey E. Prisbrey (1997). 2 This paper focuses on only standard linear games in which to contribute zero to the public good is the dominant strategy.

Does the brain consume additional glucose during self-control tasks?

A currently popular model of self-control posits that the exertion of self-control relies on a resource, which is expended by acts of self-control, resulting in less of this resource being available for subsequent acts of self-control. Recently, glucose has been proposed as the resource in question. For this model to be correct, it must be the case that A) performing a self-control task reduces glucose levels relative to a control task and B) performing a self-control task reduces glucose relative to pre-task levels. Evidence from neurophysiology suggests that (A) is unlikely to be true, and the evidence surrounding (B) is mixed, and is unlikely to be true for subjects who have not recently fasted. From the standpoint of evolved function, glucose might better be thought of as an input to decision making systems rather than as a constraint on performance.