The cover shows an artistic representation of various cancer cells. The large-scale gains, losses and rearrangements of DNA seen in chromosomal instability are a typical feature of cancer — but there is no comprehensive framework to decode the causes of this genomic variability and their possible links to disease. In this week’s issue, Florian Markowetz, Geoff Macintyre and their colleagues present such a framework with a compendium of 17 signatures of chromosomal instability that can be used to predict how tumours might respond to drugs and that help to identify future therapeutic targets. The team created the compendium by examining 7,880 tumours representing 33 types of cancer. In a separate paper, Nischalan Pillay and colleagues examined 9,873 cancers to generate 21 similar signatures of chromosomal instability.

To study inequality is to confront a world of contrasts: excessive wealth next to palpable poverty; sickness abutting health. The COVID pandemic has exposed and worsened many such disparities. This week, Nature presents a special collection of articles focusing on the researchers trying to quantify and reduce inequality. Whether they are measuring the effects of the pandemic or testing interventions to lift people out of poverty, the message is simple: gathering the right information will help to mitigate the harm caused by inequality.

The cover image shows plants growing at altitude on Altar Volcano in Chimborazo, Ecuador. Extreme altitudes pose challenges for most forms of life, and flowering plants are no exception. But flowering plants have been found growing as high as 6,400 metres above sea level. In this week’s issue, Michael Holdsworth and his colleagues reveal a molecular mechanism that helps plants to adapt to the extremes of altitude. The researchers studied a range of plants, representing four diverse clades of flowering plants — thale cress (Arabidopsis thaliana), tomato, poppy and the grass Brachypodium distachyon. They found that plants use genetic adaptations to adjust their sensitivity to atmospheric oxygen, whose partial pressure decreases with altitude. By decoding the ambient oxygen level, the plants are able to sense the altitude at which they grow and optimize internal biochemical processes.

The Casarabe people lived in southwest Amazonia around AD 500–1400, but understanding of this culture has been limited because the archaeological remains are covered in dense forest. In this week’s issue, Heiko Prümers and his colleagues reveal the discovery of new Casarabe settlements in the Bolivian Amazon. The researchers used lidar to scan the forest, revealing 2 large settlements (each covering more than 100 hectares) and 24 smaller sites, 15 of which had previously been known to exist. The cover image shows Cotoca, one of the two large settlements, in which earthen mounds (one more than 20 metres high) and long causeways can clearly be seen. The team suggests that these results are the first evidence of agrarian-based, low-density urbanism in western Amazonia. They conclude that the region was not as sparsely populated in pre-Hispanic times as was previously thought.

With six sets of chromosomes, the hexaploid cultivated oat (Avena sativa L.) has a complex evolutionary history. In this week’s issue, Nick Sirijovski and his colleagues present a high-quality reference genome for A. sativa alongside those for its close relatives the diploid Avena longiglumis and the tetraploid Avena insularis. By examining the three genomes, the researchers were able to trace genomic reorganizations in the crop’s evolution. They were also able to map the genes for important agronomic traits, highlighting gene families linked to human health and nutrition. With health and sustainability high on global agendas, the team hopes this new resource will bolster genomics-assisted breeding and trait studies to address these challenges and more.