We examined the effect of an image of a pair of eyes on contributions to an honesty box used to collect money for drinks in a university coffee room. People paid nearly three times as much for their drinks when eyes were displayed rather than a control image. This finding provides the first evidence from a naturalistic setting of the importance of cues of being watched, and hence reputational concerns, on human cooperative behaviour.

A comprehensive evolutionary framework for understanding the maintenance of heritable behavioral variation in humans is yet to be developed. Some evolutionary psychologists have argued that heritable variation will not be found in important, fitness-relevant characteristics because of the winnowing effect of natural selection. This article propounds the opposite view. Heritable variation is ubiquitous in all species, and there are a number of frameworks for understanding its persistence. The author argues that each of the Big Five dimensions of human personality can be seen as the result of a trade-off between different fitness costs and benefits. As there is no unconditionally optimal value of these trade-offs, it is to be expected that genetic diversity will be retained in the population.

Human cognition is often biased, from judgments of the time of impact of approaching objects all the way through to estimations of social outcomes in the future. We propose these effects and a host of others may all be understood from an evolutionary psychological perspective. In this article, we elaborate error management theory (EMT;Haselton & Buss, 2000). EMT These two wisdoms seem contradictory. The first urges caution, whereas the second reminds us that we have nothing to lose and should throw caution to the wind. Yet both seem to capture aspects of human psychology. A person following both maxims would be a paranoid optimist, taking chances in some domains but simultaneously being fearful of certain kinds of harm. We argue, using insights from signal detection and error management theory (EMT), that there are good evolutionary reasons why the paranoid optimist mind could evolve. Furthermore, in which domains it is best to be paranoid and in which to be optimistic is predictable from the pattern of recurrent costs and benefits associated with decisions in that domain throughout our evolutionary history. This perspective suggests that one of the curiosities of human cognition-the fact that it seems riddled with biases-may be a functional feature of mechanisms for making judgments and decisions.Human cognition has often been shown to be biased. Perceivers underestimate the time-to-impact of approaching sounds (Neuhoff, 1998(Neuhoff, , 2001) and overestimate the connection between pictures of snakes and unpleasant outcomes such as electric shocks (Tomarken, Mineka, & Cook, 1989). People also appear to have a variety of positive illusions (Taylor & Brown, 1988), which cause them to overestimate the likelihood that they will succeed in spite of the adversity they face. Evidence in these domains and many others suggests that humans possess a multitude of biases, or propensities to adopt one belief on the basis of more slender evidence than would be required to believe in an alternative.Until recently, many psychologists have been content to describe these phenomena, their contexts of appearance, and possible implications, without much concern for their ultimate origin. As Krebs and Denton (1997) noted, in as much as explanation is needed, it tends to be proximate in nature. Psychologists argue that cognition is performed by a set of simple heuristic procedures, which are effective in many circumstances but prone to error in others (e.g., Kahneman, Slovic, & Tversky, 1982;Miller & Ross, 1975). Or, in social domains, biases in judgment serve the proximate function of preserving self-esteem or subjective happiness for the ego-centered human animal (Crocker & Park, 2003;Greenberg, Pyszczynski, Solomon, & Pinel, 1993;Kunda, 1990). Researchers offer evoked biases as examples of just such imperfections. Personality and Social Psychology Review 2006, Vol. 10, No. 1, 47-66 Copyright © 2006 by Lawrence Erlbaum Associates, Inc. 47We are grateful to Clark Barrett, Daniel Fessler, Mark Schaller and two reviewers for hel...

Short abstract-Common sense says that obesity is the consequence of too much food. Adaptive reasoning says something rather different: individuals should store fat when access to food is insecure, to buffer themselves against future shortfall. Applied to humans, this principle suggests that food insecurity should be a risk factor for overweight and obesity. We provide a meta-analysis of the extensive epidemiological literature, finding that food insecurity robustly predicts high body weight, but only amongst women in high-income countries. We discuss the relevance of food insecurity to understanding the global obesity problem.Long abstract-Integrative explanations of why obesity is more prevalent in some sectors of the human population than others are lacking. Here, we outline and evaluate one candidate explanation, the insurance hypothesis (IH). The IH is rooted in adaptive evolutionary thinking: the function of storing fat is to provide a buffer against shortfall in the food supply. Thus, individuals should store more fat when they receive cues that access to food is uncertain. Applied to humans, this implies that an important proximate driver of obesity should be food insecurity rather than food abundance per se. We integrate several distinct lines of theory and evidence that bear on this hypothesis. We present a theoretical model that shows it is optimal to store more fat when food access is uncertain, and we review the experimental literature from non-human animals showing that fat reserves increase when access to food is restricted. We provide a meta-analysis of 125 epidemiological studies of the association between perceived food insecurity and high body weight in humans. There is a robust positive association, but it is restricted to adult women in high-income countries. We explore why this could be in light of the IH and our theoretical model. We conclude that whilst the IH alone cannot explain the distribution of obesity in the human population, it may represent a very important component of a pluralistic explanation. We also discuss insights it may offer into the developmental origins of obesity, dieting-induced weight gain, and Anorexia Nervosa.

Socioeconomic differences in behaviour are pervasive and well documented, but their causes are not yet well understood. Here, we make the case that a cluster of behaviours is associated with lower socioeconomic status (SES), which we call "the behavioural constellation of deprivation." We propose that the relatively limited control associated with lower SES curtails the extent to which people can expect to realise deferred rewards, leading to more present-oriented behaviour in a range of domains. We illustrate this idea using the specific factor of extrinsic mortality risk, an important factor in evolutionary theoretical models. We emphasise the idea that the present-oriented behaviours of the constellation are a contextually appropriate response to structural and ecological factors rather than a pathology or a failure of willpower. We highlight some principles from evolutionary theoretical models that can deepen our understanding of how socioeconomic inequalities can become amplified and embedded. These principles are that (1) small initial disparities can lead to larger eventual inequalities, (2) feedback loops can embed early-life circumstances, (3) constraints can breed further constraints, and (4) feedback loops can operate over generations. We discuss some of the mechanisms by which SES may influence behaviour. We then review how the contextually appropriate response perspective that we have outlined fits with other findings about control and temporal discounting. Finally, we discuss the implications of this interpretation for research and policy.