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 predicts that if judgments are made under uncertainty, and the costs of false positive and false negative errors have been asymmetric over evolutionary history, selection should have favored a bias toward making the least costly error. This perspective integrates a diverse array of effects under a single explanatory umbrella, and it yields new content-specific predictions.

Developmental plasticity describes situations where a specific input during an individual's development produces a lasting alteration in phenotype. Some instances of developmental plasticity may be adaptive, meaning that the tendency to produce the phenotype conditional on having experienced the developmental input has been under positive selection. We discuss the necessary assumptions and predictions of hypotheses concerning adaptive developmental plasticity (ADP) and develop guidelines for how to test empirically whether a particular example is adaptive. Central to our analysis is the distinction between two kinds of ADP: informational, where the developmental input provides information about the future environment, and somatic state-based, where the developmental input enduringly alters some aspect of the individual's somatic state. Both types are likely to exist in nature, but evolve under different conditions. In all cases of ADP, the expected fitness of individuals who experience the input and develop the phenotype should be higher than that of those who experience the input and do not develop the phenotype, while the expected fitness of those who do not experience the input and do not develop the phenotype should be higher than those who do not experience the input and do develop the phenotype. We describe ancillary predictions that are specific to just one of the two types of ADP and thus distinguish between them.

Where the expected reproductive life span is short, theory predicts that individuals should follow a “fast” life-history strategy of early reproduction, reduced investment in each offspring, and high reproductive rate. I apply this prediction to different neighborhood environments in contemporary England. There are substantial differences in the expectation of healthy life between the most deprived and most affluent neighborhoods. Using data from the Millennium Cohort Study (n = 8660 families), I show that in deprived neighborhoods compared with affluent ones, age at first birth is younger, birthweights are lower, and breastfeeding duration is shorter. There is also indirect evidence that reproductive rates are higher. Coresidence of a father figure is less common, and contact with maternal grandmothers is less frequent, though grandmaternal contact shows a curvilinear relationship with neighborhood quality. Children from deprived neighborhoods perform less well on a verbal cognitive assessment at age 5 years, and this deficit is partly mediated by parental age and investment variables. I suggest that fast life history is a comprehensible response, produced through phenotypic plasticity, to the ecological context of poverty, but one that entails specific costs to children.