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<jats:p>Armed conflicts have been prevalent throughout history, in some cases having very great consequences. To win, one needs to understand the characteristics of an armed conflict and be prepared with resources and capabilities for responding to its specific challenges. An important tool for understanding these characteristics and challenges is a model—an abstraction of the field of conflict. Models have evolved through the years, addressing different conflict scenarios with varying techniques.</jats:p>

<jats:p>Current debates over the relation between climate change and conflict originate in a lack of data, as well as the complexity of pathways connecting the two phenomena.</jats:p>

<jats:p>The most methodologically rigorous epidemiological study on American military personnel deployed to Iraq and Afghanistan found that 4.3% of troops developed posttraumatic stress disorder (PTSD). Among deployed combatants, 7.6% developed PTSD, whereas 1.4% of deployed noncombatants did so. The U.S. Department of Veterans Affairs has launched a program ensuring that all veterans with PTSD will receive evidence-based cognitive-behavioral therapy, and the Army has developed Battlemind postdeployment early interventions that reduce risk for the disorder.</jats:p>

<jats:p>The view of humans as violent war-prone apes is poorly supported by archaeological evidence and only partly supported by the behavior of our closest primate relatives, chimpanzees and bonobos. Whereas the first species is marked by xenophobia, the second is relatively peaceful and highly empathic in both behavior and brain organization. Animal empathy is best regarded as a multilayered phenomenon, built around motor mirroring and shared neural representations at basal levels, that develops into more advanced cognitive perspective-taking in large-brained species. As indicated by both observational and experimental studies on our closest relatives, empathy may be the main motivator of prosocial behavior.</jats:p>

<jats:p>The origins of such varied features of contemporary life as the national state and the desire to uphold generous and civic social norms are to be found in a combination of conflict between groups and attenuation of both inequalities and conflicts within groups. In contrast to the adoption of a better tool or a more productive crop, which can be adopted by a single individual, a new institution works only if most people adopt it. This explains why collective action against those benefitting from the status quo at the expense of others, as well as conflict between groups governed by different norms and institutions, figures so prominently in our capacity to adapt to changing circumstances and to harness new knowledge for human benefit.</jats:p>

<jats:p>An emerging evolutionary perspective suggests that nature and human nature are less “red in tooth and claw” than generally acknowledged by a competition-based view of the biological world. War is not always present in human societies. Peace systems, defined as groups of neighboring societies that do not make war on each other, exist on different continents. A comparison of three peace systems—the Upper Xingu River basin tribes of Brazil, the Iroquois Confederacy of upper New York State, and the European Union—highlight six features hypothesized to be important in the creation and maintenance of intersocietal peace: (i) an overarching social identity, (ii) interconnections among subgroups, (iii) interdependence, (iv) nonwarring values, (v) symbolism and ceremonies that reinforce peace, and (vi) superordinate institutions for conflict management. The existence of peace systems demonstrates that it is possible to create social systems free of war.</jats:p>

<jats:p>Phylogenetic analysis of the mitochondrial calcium transporter shows that it was a feature of early eukaryotes.</jats:p>

<jats:title>Ultimate Blockade</jats:title> <jats:p> A Rydberg atom has an electron in a highly excited energy state, close to being set free, but not quite. Ensembles of such atoms interact strongly, sometimes leading to blockade effects where the excitation of one atom prevents the excitation of another. <jats:bold>Dudin and Kuzmich</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="887" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217901">887</jats:related-article> , published online 19 April; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6083" page="812" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222815">Grangier</jats:related-article> </jats:bold> ) demonstrate the generation of a many-body excitation with no more than one Rydberg atom in a mesoscopic ensemble of ultracold atoms. When the principal quantum number was increased beyond 70, the excitation was converted into a photon. The ability to control the creation of excitations provides a promising system for quantum information storage, as well as a source of correlated photons. </jats:p>

<jats:title>Water-Assisted Proton Diffusion</jats:title> <jats:p> Proton diffusion on metal oxide surfaces can play an important role in many catalytic processes. The presence of water is thought to accelerate proton diffusion. <jats:bold> Merte <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="889" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219468">889</jats:related-article> ) used high-speed, high-resolution scanning tunneling microscopy to study proton diffusion on an iron oxide. On oxygen-terminated FeO monolayer films formed on Pt, molecular water accelerated proton diffusion. Density function theory calculations implicated a H <jats:sub>3</jats:sub> O <jats:sup>+</jats:sup> transition state in the diffusion process. </jats:p>

<jats:title>Mechanisms in Methanol Catalysis</jats:title> <jats:p> The industrial production of methanol from hydrogen and carbon monoxide depends on the use of copper and zinc oxide nanoparticles on alumina oxide supports. This catalyst is “structure sensitive”; its activity can vary by orders of magnitude, depending on how it is prepared. <jats:bold> Behrens <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="893" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219831">893</jats:related-article> , published online 19 April; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6083" page="810" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222974">Greeley</jats:related-article> </jats:bold> ) used a combination of bulk and surface-sensitive analysis and imaging methods—along with insights from density functional theory calculations—to study several catalysts, including the one similar to that used industrially. High activity depended on the presence of steps on the copper nanoparticles stabilized by defects such as stacking faults. Partial coverage of the copper nanoparticles with zinc oxide was critical for stabilizing surface intermediates such as HCO and lowering energetic barriers to the methanol product. </jats:p>