Letters

When given time to deliberate in an economic game, individuals become less cooperative. Grossmann and colleagues show that players directed toward a third-person perspective reorientate from selfish to common goals and maintain cooperation.

Orangutan kiss-squeaks — voiceless consonant-like calls — exhibit rich acoustic variation and clear acoustic signature, conveying information about population, size class, context and individual identity.

By developing wireless sensors to track social interactions among hunter-gatherers in the Republic of the Congo and the Philippines, Migliano et al. find that a few strong friendship ties connecting unrelated families lead to more efficient social networks.

Pah et al. analyse gun violence incidents at US schools for the period 1990–2013 and find heightened rates in the period 2007–2013. Indicators of economic distress significantly correlate with increases in the rate of gun violence.

Over six experiments, Kanakogi et al. show that infants as young as 6 months support third-party interventions that protect victims from aggressors. This suggests that human emphasis upon such acts is rooted within the preverbal infant’s mind.

Using ultra-high-field functional magnetic resonance imaging, the authors identify six widely separated maps in the human cortex that code for numerosity (the number of objects in a set).

By analysing the supermarket purchases of more than 280,000 people over several years, Riefer et al. show that people’s preferences follow their choices, rather than the other way around.

Using whole-genome data for single-nucleotide polymorphism and results from genome-wide association studies, the authors show that people’s preference for pairing with those with similar phenotypic traits has genetic causes and consequences.

Gomez-Lievano and colleagues develop a new theory of scaling in cities — how the prevalence of phenomena such as education and crime changes with population size — by unifying models of economic complexity and cultural evolution.

He and colleagues show that attention plays a key role in anchoring visual orientation in 3D space. The effect of attention was contingent on the ground being visible, suggesting our terrestrial visual system is best served by its ecological niche.

The authors asked human participants to listen to and imitate randomly generated drumming sequences from each other. Participants turned initially random sequences into rhythmically structured patterns that are characterized by all six statistical universals found in world music.

Koizumi and colleagues show that it is possible to reduce fear without explicit representations of feared objects by pairing rewards with activation patterns in the visual cortex that represent a conditioned stimulus, while participants remain unaware of the purpose of the procedure.

Decreases in pathogen prevalence in the US and the UK over the past several decades are linked to reduced gender inequality. These shifts in rates of infectious disease precede shifts in gender inequality, suggesting a causal link.

Faces are positioned in a statistical distribution of faces extracted from the environment. Social inferences from faces (for example, trustworthiness) arise from the statistical position of faces in this learned distribution.