Nature.com Palaeontology: Trilobites laid eggs 2017-01-18T00:00:00.000000Z The discovery that extinct marine organisms called trilobites laid eggs provides the first direct evidence for how they reproduced.Trilobites lived between 520 million and 250 million years ago, and are one of the earliest known groups of arthropods (invertebrates, including modern insects, with exo... Ecology: Trees grow thick skin to survive fire 2017-01-18T00:00:00.000000Z Trees that live in fire-prone areas have evolved thick bark to protect themselves. This trait can be used as an indicator of how resilient a tree species is to increased fire risk under global warming.Adam Pellegrini, now at Stanford University in California, and his Chemistry: Molecule gets knotted 2017-01-18T00:00:00.000000Z Scientists have braided a molecule into a knot with eight crossings, the most complex yet made in the lab.Flexible polymers can twist themselves into complex knots, but scientists have struggled to create all but the simplest structures. David Leigh and his colleagues at the Neuroscience: How to turn on killer instinct 2017-01-18T00:00:00.000000Z The activation of a particular group of brain cells is all it takes to make mice hunt to kill.The brain's central amygdala has long been thought to have a role in producing emotions, particularly fear. To activate this brain region, Ivan de Araujo at Animal behaviour: Faecal odours act as rhino signals 2017-01-18T00:00:00.000000Z White rhinos can learn about each other by sniffing one another's faeces.Many mammals communicate through smells in their urine. To see whether faeces have a similar role, Courtney Marneweck at the University of KwaZulu-Natal in Pietermaritzburg, South Africa, and her colleagues analysed odours from... Base the social cost of carbon on the science 2017-01-18T00:00:00.000000Z The potential economic damage from global warming should not be influenced by politics. Replication studies offer much more than technical details 2017-01-18T00:00:00.000000Z They demonstrate the practice of science at its best. Anthropocene: social science misconstrued 2017-01-18T00:00:00.000000Z Adding in a wider range of social-science expertise will not, in my view, help efforts to 'formalize the Anthropocene' as a geological age of human influence (E.Elliset al. Nature540, 192–193;10.1038/540192a2016). The authors rightly Books in brief 2017-01-18T00:00:00.000000Z Barbara Kiser reviews five of the week's best science picks. Technology: He wrote the future 2017-01-18T00:00:00.000000Z On Arthur C. Clarke's centenary, Andrew Robinson lauds a prescient, original writer.