Hadza women Chausiki and Sislem (with baby) pick ngwilabee berries. The Hadza of northern Tanzania are almost totally cut off from the modern developed world, providing anthropologists with a useful model of an early hunter-gatherer society. A study of Hadza social networks, quantifying their ties to each other and their propensity to cooperate, shows that the main characteristics of modernized networks, such as transitivity and homophily, are observed in the Hadza. In addition, social ties are more likely between individuals with similar levels of public goods game donations, and Hadza camps exhibit high between-group and low within-group variation in cooperation. Taken together, these results provide the strongest evidence so far that these key features of human networks reflect shared ancestry and may have developed at an early point in human history. Photo: Martin Schoeller/August

Philanthropic research funding has become increasingly important in recent years, but much of it comes at a cost: charities rarely pay the full overheads of research, and agenda-driven funding sources may skew research priorities. In a Comment piece, Patrick Aebischer argues that universities should levy ‘full economic costs in their dealings with charities in order to cover additional expenses such as buildings, maintenance and staff. Cover art: 2&3 Illustration.

In 1969—a few years after unearthing the first Velociraptor fossil—John Ostrom speculated that theropod dinosaurs used their tails as dynamic stabilizers during active or irregular movements. A study combining computer modelling, video observation of leaping agama lizards (Agama agama) and the construction of a robot with a lizard-like tail provides support for Ostrom’s hypothesis. The results (see videos in Supplementary Information) show that, using sensory feedback, active tails can stabilize body attitude mid-air by transferring angular momentum from body to tail. The inertia of swinging appendages has also been invoked as a stabilizing factor in primates and other animals, so these findings are relevant to our understanding of appendage evolution in general. They may also provide biological inspiration for the design of highly manoeuvrable search-and-rescue robots using tails. Cover: A. agama leaping to a vertical surface from a low-friction vault.

The radio source Sgr A* in Sagittarius is thought to be the site of a supermassive black hole lying at the centre of the Milky Way. A study of stellar orbits has identified an object moving towards Sgr A* at a speed of 1,700 kilometres per second. Its low temperature and spectral properties suggest that it is a dusty cloud of ionized gas, three times the mass of Earth, in the process of falling into the black hole. Models predict that as the cloud gets closer to the black hole, X-ray emissions will become much brighter, and a giant radiation flare may be emitted in a few years if the cloud breaks up and feeds gas into the black hole. On the cover, a hydrodynamical simulation set in the year 2025 shows the tidally disrupted gas cloud interacting with the hot accretion flow. In the background are S-stars for which orbits have been determined. (Simulation by M. Schartmann (MPE) using the PLUTO code.)