Much of human cooperation remains an evolutionary riddle. Unlike other animals, people frequently cooperate with non-relatives in large groups. Evolutionary models of large-scale cooperation require not just incentives for cooperation, but also a credible disincentive for free riding. Various theoretical solutions have been proposed and experimentally explored, including reputation monitoring and diffuse punishment. Here, we empirically examine an alternative theoretical proposal: responsibility for punishment can be borne by one specific individual. This experiment shows that allowing a single individual to punish increases cooperation to the same level as allowing each group member to punish and results in greater group profits. These results suggest a potential key function of leadership in human groups and provides further evidence supporting that humans will readily and knowingly behave altruistically.

The pursuit of social rank pervades all human societies and the position that an individual occupies within a hierarchy has important effects on their social and reproductive success. Whilst recent research has indicated that there are two distinct routes to rank attainmentdominance (through the induction of fear) and prestige (through respect and admiration)this empirical evidence has generally provided only a cross-sectional snapshot of how the two processes operate in human hierarchy. Whether dominance and prestige are potentially viable long-term strategies, rather than more effective short-term tactics, for acquiring rank in groups remains an open question. The current research addresses this gap by examining the temporal dynamics between prestige, dominance and social rank using a dynamic, evolutionary approach to understanding human social hierarchy, and thus supplies the first longitudinal empirical assessment of these variables' relationships. Using naturalistic student project groups comprised of 3-5 teammates, the present research tracks the temporal relationships between prestige, dominance and social rank-provided through round-robin teammate-ratings-from the initial formation of collaborative task groups through to the end of a 16-week long academic semester. Results indicate that, whilst dominance and prestige both promoted social rank in unacquainted groups initially and were distinct processes throughout the period examined, only prestige had a positive effect on social rank over time. Further results reveal that the temporal relationship between prestige and social rank was bidirectional, such that acquiring social rank further perpetuates future prestige. Overall, findings present a framework for the longitudinal distinction between prestige and dominance.

The moderating role of individual difference variables (Self-Reported Habit Index [SRHI], Need for Cognition [NFC]) on relationships between implicit (Implicit Association Test [IAT], Extrinsic Affective Simon Test [EAST]) or explicit measures of attitude and behavior is assessed in two studies. A dissociation pattern is found on self-report diary measures of behavior. In Study 1, the EAST-behavior relationship is moderated by SRHI; explicit measures of the attitude-behavior relationship are moderated by NFC. In Study 2, the IAT-behavior relationship is moderated by SRHI; explicit measures of the attitude-behavior relationship are moderated by NFC. Higher levels of SRHI and NFC are associated with stronger relationships between the implicit or explicit measures of attitude and the measure of behavior. In Study 2, the SRHI x IAT interaction is replicated for an objective behavior measure. Implications for understanding the relationship between implicit and explicit measures of attitudes and measures of behavior are discussed.

The concept of a group as comparable to a single organism has had a long and turbulent history. Currently, methodological individualism dominates in many areas of psychology and evolution, but natural selection is now known to operate at multiple levels of the biological hierarchy. When between-group selection dominates within-group selection, a major evolutionary transition occurs and the group becomes a new, higher-level organism. It is likely that human evolution represents a major transition, and this has wide-ranging implications for the psychological study of group behavior, cognition, and culture.

Word counts: 5040Implicit Food Preference -2 -The IAT as a predictor of food choice: The case of fruits versus snacks Abstract One of the issues concerning the application of implicit measures like the IAT is whether they can be successfully applied to consumer choices. Four studies (N=399) tested the predictive and incremental validity of an IAT of attitudes towards fruits versus snacks on the choice of a fruit or a snack at the end of the experimental session. Specifically, additive and interactive patterns to predict behavioral preference towards snacks or fruits were tested.The results showed that the IAT has both predictive and incremental validity and supported the additive pattern (i.e., both implicit and explicit measures independently predicted the behavioral preference for fruits versus snacks).Implicit Food Preference -3 -Since its introduction by Greenwald, McGhee and Schwartz (1998), the Implicit Association Test has been the most frequently used measure for assessing implicit attitudes.The IAT is a computerized paradigm that measures indirectly the strength of the association between pairs of concepts (e.g., two target categories: fruits and snacks; two attribute categories: positive and negative) via a classification task. The IAT score is computed by subtracting the average response time of the two versions of the combined classification task (i.e., two pairings of target-attribute: fruits-positive and fruits-negative) in which stimuli from all categories are randomly presented. The assumption underlying the IAT is that if two concepts are highly associated (e.g., fruits and positive), the classification task will be easier (and the participants quicker to respond) when the associated concepts share the same response key than when they require a different response key (for a more detailed description, see Greenwald et al., 1998). Theoretically based on an associative network conceptualization of a Social Knowledge Structure in memory (see Greenwald, Banaji, Rudman, Farnham, Nosek, & Mellot, 2002) and on the conceptualization of an attitude as the association between an attitude-object and a valence concept (Fazio, 1995), the IAT is assumed to reflect the relative strength of automatic associations between concepts. The IAT has been used as an implicit measure of attitudes, self-concepts, and stereotypes (for reviews, see Greenwald & Nosek, 2001; Hofmann, Gawronski, Gschwender, Lee, & Schmitt, 2005;Poehlman, Uhlmann, Greenwald, & Banaji, 2006). Numerous studies have shown the reliability of the IAT in various domains, with values generally hovering around .80 for the internal consistency and .60 for test-retest stability (e.g., Dasgupta & Greenwald, 2001;Greenwald & Farnham, 2000;Greenwald & Nosek, 2001;Perugini, 2005a).Predictive validity.One of the key issues concerning the IAT is its ability to predict relevant behaviors. In fact, one could argue that, both on practical and theoretical grounds, an acid test for a measure Implicit Food Preference -4 -such as the IAT is whether it shows evidence ...