The cover shows an artist’s impression of a frozen microwave antenna surrounded by very cold molecules. Gases of polar molecules offer greater potential than atomic gases for probing quantum effects, but they first need to be cooled sufficiently, which is a challenge. In this week’s issue, Andreas Schindewolf and his colleagues present a method for cooling polar molecules to the point where the gas becomes degenerate and quantum effects dominate. To do this, the researchers use tailored microwave fields to introduce repulsive barriers that prevent loss-inducing reactions between molecules from occurring. The result is that the molecules are readily cooled through elastic collisions to 21 nanokelvin, generating a 3D dipolar quantum gas of interacting molecules.

The cover shows an artistic impression of marine life in Indonesia’s coral reefs. The question of whether there are limits to biodiversity in the seas is typically addressed by examining the fossil record. In this week’s issue, Pedro Cermeño and his colleagues present a model that combines the fossil record with plate tectonics and Earth’s environmental conditions to offer insight into regional diversification of marine invertebrates. The researchers used the model to examine how biodiversity recovered after mass extinctions during the Phanerozoic eon, covering some 500 million years of Earth’s history. They found that throughout the Phanerozoic, less than 2% of area of the globe covered by water showed signs of diversity levels reaching saturation. The team also note that as Pangaea broke up into continents, the stability of Earth’s environmental conditions allowed the development of diversity hotspots that helped to drive an increase in biodiversity in the late Mesozoic and Cenozoic eras.

Although the domestic dog can trace its origins to the grey wolf (Canis lupus), exactly when, where and how domestication happened has remained a source of debate. In this week’s issue, Anders Bergström, Pontus Skoglund and their colleagues, take a step towards resolving this question. The researchers analysed the genomes of 72 ancient wolves from across Europe, Siberia and North America, and spanning the past 100,000 years. They found that dogs are most closely related to ancient wolves from eastern Eurasia but that dogs in the Near East and Africa derive up to half their ancestry from a distinct population related to modern southwest Eurasian wolves. Although none of the genomes analysed was a direct match for either dog ancestry, the researchers say that it has narrowed down where next to look for the ancestors of domestic dogs.

On 4 July 2012, researchers at the Large Hadron Collider (LHC) made a long-awaited announcement: they had finally obtained evidence that affirmed the existence of the Higgs boson. In this week’s issue, teams from the two main experiments at the LHC present analyses of all the data collected on the particle since its discovery. The standard model of particle physics predicts that coupling between the Higgs boson and any given particle should be proportional to their mass — the results from CMS and ATLAS experiments show that, for the heavy particles they have been able to observe, the data are in line with predictions. A Perspective article goes on to offer an overview of what we have learnt about the particle so far — and how closer scrutiny of it might be key to some of the most important open questions in fundamental physics.