Many recent experiments in the field of behavioural economics appear to demonstrate a willingness of humans to behave altruistically, even when it is not in their interest to do so. This has led to the assertion that humans have evolved a special predisposition towards altruism. Recent studies have questioned this, and demonstrated that selfless cooperation does not hold up in controlled experi...

The degree of human cooperation among strangers is a major evolutionary puzzle. A prominent explanation is that cooperation is maintained because many individuals have a predisposition to punish those violating group-beneficial norms. A critical condition for cooperation to evolve in evolutionary models is that punishment increases with the severity of the violation. Here we present evidence fr...

How do human groups maintain a high level of cooperation despite a low level of genetic relatedness among group members? We suggest that many humans have a predisposition to punish those who violate group-beneficial norms, even when this imposes a fitness cost on the punisher. Such altruistic punishment is widely observed to sustain high levels of cooperation in behavioral experiments and in na...

After 38 years of longevity (1970 to 2008), including huge growth over its last decade, in 2008 and 2009 the Association of Community Organizations for Reform Now (ACORN) was rocked by an embezzlement scandal and two controversies and declined precipitously. By the spring of 2010, all city and statewide ACORN operations had either disaffiliated from the national organization or collapsed altoge...

We calculate the linear and nonlinear susceptibilities of periodic longitudinal chains of hydrogen dimers with different bond-length alternations using a diffusion quantum Monte Carlo approach. These quantities are derived from the changes in electronic polarization as a function of applied finite electric field--an approach we recently introduced and made possible by the use of a Berry-phase, ...