Editors' Choice

Science  29 Jul 2016:
Vol. 353, Issue 6298, pp. 459
  1. Evolutionary Cognition

    The quizzical gaze of goats

    1. Guy Riddihough

    Goats look to humans for assistance with difficult tasks.


    Dogs were domesticated by humans, most likely for companionship and work, tasks that require considerable interaction between human and dog. Goats, on the other hand, were probably domesticated for their produce—meat, leather, and milk. Nawroth et al. presented goats habituated to humans with an “unsolvable problem,” a task wherein a food reward is visible but inaccessible. During the test, goats glanced earlier, more frequently, and more often between the food and a nearby forward-facing human than at a human facing away from the goat. This behavior has also been seen in dogs, suggesting that domestication, regardless of motivation, has broadly influenced the evolution of animal cognition and the relationship between us and the animals we raise.

    Biol. Lett. 10.1098/rsbl.2016.0283 (2016).

  2. Cancer Genomics

    Immune differences in colorectal cancers

    1. Laura M. Zahn

    Synchronous colorectal cancers (SCCs) occur when more than one malignant lesion is present within the colon at a time. Cereda et al. exome-sequenced paired tumors and matched normal samples across 10 patients with SCCs. High tumor heterogenity was observed, suggesting independent underlying genetic origins of tumors in at least 7 of the 10 patients examined. Comparisons of multiple-tumor patients with individuals who had only a single colorectal tumor revealed germline (nontumor) enrichment of mutations in immune-related genes, as well as different immune cell composition in the normal colonic mucosa and higher tumor-associated inflammation. These data suggest that impaired immune processes may be a factor in SCCs.

    Nat. Comm. 10.1038/ncomms12072 (2016).

  3. Structural Biology

    Halogens instead of hydroxyls

    1. Nicholas S. Wigginton

    Chlorine and other halogens are key constituents of many industrially important compounds. Enzyme-based approaches to transfer halogens to organic compounds are a potentially greener synthetic route, producing less harmful by-products. Mitchell et al. determined a 2.4 Å-resolution x-ray crystal structure of a bacterial halogenase protein in a complex with its precursor substrate. The structure reveals how the enzyme chlorinates the substrate through an iron-chlorine intermediate at the active site. A neighboring serine orchestrates ligand dynamics to allow for halogenation instead of hydroxylation. Engineering a related nonhalogenating hydroxylase protein with a serine in the same position makes the enzyme capable of both hydroxylation and halogenation.

    Nat. Chem. Biol. 10.1038/NCHEMBIO.2112 (2016).

  4. Nanotechnology

    Painting the target for fluorescent imaging

    1. Valda Vinson

    Superresolution fluorescence techniques have reached resolutions between 10 and 20 nm. However, imaging individual molecules in a densely packed cluster remains challenging. Dai et al. use the method DNA-PAINT, in which a fluorophore-labeled imaging strand is transiently bound to a target-bound docking strand to visualize individual targets in a grid of DNA nanostructures with a point-to-point target spacing of 5 nm. The imaging strands are continuously replenished, allowing high photon counts. Good target separation comes from regulating the binding kinetics to give a large number of blinking events, and tuning the blinking cycles produces a good signal-to-noise ratio. In addition, using DNA nanostructures as fiduciary markers allows for the correction of stage drift over long imaging times.

    Nat. Nanotechnol. 10.1038/NNANO.2016.95 (2016).

  5. Materials Science

    Stretchy and sensitive skin

    1. Marc S. Lavine

    Natural skin is both highly elastic and sensitive to small pressure changes, but this combination of properties has been hard to engineer into an electronic skin. Duan et al. built a double polymer network structure around nanofiber-containing chitosan microspheres that act as reinforcements, yielding a material with a highly stretchable, wrinkled structure. Dried chitosan microspheres were swollen in acid containing acrylamide that was polymerized to form a chitosan-polyacrylamide gel. In a subsequent step, the gels were soaked in acid containing aniline that was polymerized in situ. The resulting gels show excellent conductivity and force sensitivity with a wide pressure detection range.

    Adv. Mater. 10.1002/adma.201602126 (2016).

  6. Brain Anatomy

    Does size matter?

    1. Peter Stern

    Contrary to historical perception, although their brains are small, birds are surprisingly smart. Olkowicz et al. compared neuronal numbers across mammalian and bird species with similar brain mass. They found that parrot and songbird brains have twice as many nerve cells as mammalian brains of equivalent size. Their neurons are more densely packed than those of any mammal, even primates. What is more, corvids (crows, jays, and ravens) and songbirds have an exceptionally high percentage of neurons located in brain structures that are the avian homolog of the neocortex. The extremely high packing density of bird brains leads to short interneuronal distances. This results in high information processing speeds, which might further enhance the cognitive abilities of some species. Intelligence may depend more on the absolute number and connections of neurons than on brain size.

    Proc. Nat. Acad. U.S.A. 113, 7255 (2016).

  7. Physics

    A quantum test of free fall

    1. Ian S. Osborne

    The Leaning Tower of Pisa, Italy


    Galileo Galilei is purported to have dropped objects of different mass from the Leaning Tower of Pisa to demonstrate that they fall at the same rate. In formulating his general theory of relativity, Einstein described this as the universality of free fall—that all objects, irrespective of their mass, will behave identically when subject to the same gravitational field. Taking this into the quantum regime, Duan et al. performed Galileo's drop experiment with rubidium atoms of different quantum mechanical spins. With a sensitive atom-interferometer setup, they showed that the atoms fall at the same rate to within one part in 10 million, upholding Einstein's universality proposition for now. While we await a theory that can unify relativity and the principles of quantum mechanics, such precision-based experimental tests should help place bounds on any proposed theories of quantum gravity.

    Phys. Rev. Lett. 117, 023001 (2016).