The facial feedback hypothesis argues that people’s emotions are influenced by their facial expressions. The Many Smiles Collaboration — a multicentre, international adversarial collaboration — put the facial feedback hypothesis to a rigorous test in a Registered Report. They found robust evidence in support of the facial feedback hypothesis in tasks that involved mimicry or voluntary facial action, but not when facial expressions were manipulated unobtrusively (with a pen-in-mouth task). The work exemplifies the value of the Registered Report format and of adversarial collaboration in advancing credibility and knowledge.

See Coles et al.

As the climate clock is ticking closer to tipping points, the time for urgent, decisive action is now. This issue features a Focus on human behaviour and climate change, in collaboration with Nature Climate Change. The Focus includes a broad range of Review and Opinion content on the role of human behaviour in adaption to climate change and mitigation of its negative consequences.

Are all communities equally vulnerable to wildfire-smoke exposure? Do government policies that rely on people to limit their own exposure to wildfire smoke work? Burke and colleagues address these questions in the context of Californian wildfires, using data from private pollution sensors, cell phones, social media posts and internet search activity. They find that wealthier households and lower-income households respond differently to smoke events when it comes to seeking health protection information or staying at home. They also find that indoor PM2.5 concentrations are well above health guidelines, with enormous variability among households. These findings suggest that government policies that rely on people’s initiatives alone are broadly ineffective, with unequal benefits for different socioeconomic groups.

See Burke et al.See also News & Views by Hervieux-Moore and Dominici

The human capacity to synchronize to a musical beat is a heritable complex trait. Niarchou et al. identify 69 genomic loci associated with people’s synchronization to a musical beat, revealing the highly polygenic architecture of this capacity. The authors also show that the genetic architecture of beat synchronization is enriched for genes involved in early brain development and lifelong brain function.

See Niarchou et al.

Newborn infants are able to perceive phonemes — the smallest units of speech — but it is unclear whether this is an innate ability or learnt after birth. Wu et al. show that the brains of newborns can rapidly learn to discriminate phonemes within the first few hours of life.

See Wu et al. See also Research Briefing

Nonsuicidal self-injury is a risk factor for future suicide attempts, and it is estimated that 17% of adolescents worldwide engage in nonsuicidal self-injury. Kuehn et al. carried out an individual-participant meta-analysis of longitudinal studies and found support for the hypothesis that self-injurious thoughts and behaviours function to provide relief from distressing negative affect.

See Kuehn et al.

The Russian invasion of Ukraine has wreaked death and destruction in the country, with wide-ranging impacts on the global world order. This Focus highlights the experiences of Ukrainian scientists — at home and abroad — and provides insights into the many impacts of the war, including food insecurity, sanctions, disinformation, cyberwarfare, mental health and the refugee crisis.

Leveraging a global dataset of wearable device data for approximately 20,000 individuals, Jonasdottir and colleagues show how sleep away from home depends on the sleep needs of the individual: when travelling, underslept people tend to sleep more, whereas well-rested individuals tend to sleep less.

See Jonasdottir et al.

Love is a central value of modern societies, but it wasn’t always so. Combining literary history, cultural evolution, causal methods and model-based analysis, Baumard et al. provide evidence suggesting that the flourishing of romantic love, as recorded in literary fiction, is the product of economic development.

See Baumard et al. See also News & Views by Bille

Using around 600 genetic matches of elephant tusks from the same individual or close relatives, from 49 ivory seizures across Africa, Wasser et al. reveal the scale, connectivity and movements of transnational criminal organizations that trade in ivory.

See Wasser et al. See also News & Views by Jacquet

Equitable distribution of resources to fight COVID-19 is a global challenge. In a collection of research and opinion articles, researchers, public health officials, intellectual property experts, leaders of international organizations, and activists explain how global inequities in COVID-19 vaccine allocation continue fuelling the pandemic, and discuss ways to address these disparities.

See Editorial

This month, we are celebrating our fifth anniversary with two dedicated Features. In one Feature, we asked 22 leading scientists in some of the key disciplines we cover to share their vision of the future of research in their disciplines. In a second Feature, past and present editors of the journal highlight some of their favourite papers and what made them special.

See Editorial, See also Box-Steffensmeier et al. and See also Antusch et al.