Color and motion information are thought to be channeled through separate neural pathways, but it remains unclear whether and how these pathways interact to improve motion perception. In insects, such as Drosophila, it has long been believed that motion information is fed exclusively by one spectral class of photoreceptor, so-called R1 to R6 cells; whereas R7 and R8 photoreceptors, which exist in multiple spectral classes, subserve color vision. Here, we report that R7 and R8 also contribute to the motion pathway. By using electrophysiological, optical, and behavioral assays, we found that R7/R8 information converge with and shape the motion pathway output, explaining flies' broadly tuned optomotor behavior by its composite responses. Our results demonstrate that inputs from photoreceptors of different spectral sensitivities improve motion discrimination, increasing robustness of perception.

Microbial communities can subsist at depth in marine sediments without fresh supply of organic matter for millions of years. At threshold sedimentation rates of 1 millimeter per 1000 years, the low rates of microbial community metabolism in the North Pacific Gyre allow sediments to remain oxygenated tens of meters below the sea floor. We found that the oxygen respiration rates dropped from 10 micromoles of O(2) liter(-1) year(-1) near the sediment-water interface to 0.001 micromoles of O(2) liter(-1) year(-1) at 30-meter depth within 86 million-year-old sediment. The cell-specific respiration rate decreased with depth but stabilized at around 10(-3) femtomoles of O(2) cell(-1) day(-1) 10 meters below the seafloor. This result indicated that the community size is controlled by the rate of carbon oxidation and thereby by the low available energy flux.

Eubacteria inactivate their ribosomes as 100S dimers or 70S monomers upon entry into stationary phase. In Escherichia coli, 100S dimer formation is mediated by ribosome modulation factor (RMF) and hibernation promoting factor (HPF), or alternatively, the YfiA protein inactivates ribosomes as 70S monomers. Here, we present high-resolution crystal structures of the Thermus thermophilus 70S ribosome in complex with each of these stationary-phase factors. The binding site of RMF overlaps with that of the messenger RNA (mRNA) Shine-Dalgarno sequence, which prevents the interaction between the mRNA and the 16S ribosomal RNA. The nearly identical binding sites of HPF and YfiA overlap with those of the mRNA, transfer RNA, and initiation factors, which prevents translation initiation. The binding of RMF and HPF, but not YfiA, to the ribosome induces a conformational change of the 30S head domain that promotes 100S dimer formation.

Cells must balance the cost and benefit of protein expression to optimize organismal fitness. The lac operon of the bacterium Escherichia coli has been a model for quantifying the physiological impact of costly protein production and for elucidating the resulting regulatory mechanisms. We report quantitative fitness measurements in 27 redesigned operons that suggested that protein production is not the primary origin of fitness costs. Instead, we discovered that the lac permease activity, which relates linearly to cost, is the major physiological burden to the cell. These findings explain control points in the lac operon that minimize the cost of lac permease activity, not protein expression. Characterizing similar relationships in other systems will be important to map the impact of cost/benefit tradeoffs on cell physiology and regulation.

Controversy surrounds occupational health and safety regulators, with some observers claiming that workplace regulations damage firms' competitiveness and destroy jobs and others arguing that they make workplaces safer at little cost to employers and employees. We analyzed a natural field experiment to examine how workplace safety inspections affected injury rates and other outcomes. We compared 409 randomly inspected establishments in California with 409 matched-control establishments that were eligible, but not chosen, for inspection. Compared with controls, randomly inspected employers experienced a 9.4% decline in injury rates (95% confidence interval =-0.177 to -0.021) and a 26% reduction in injury cost (95% confidence interval =-0.513 to -0.083). We find no evidence that these improvements came at the expense of employment, sales, credit ratings, or firm survival.

Conspecific negative density-dependent establishment, in which local abundance negatively affects establishment of conspecific seedlings through host-specific enemies, can influence species diversity of plant communities, but the generality of this process is not well understood. We tested the strength of density dependence using the United States Forest Service's Forest Inventory and Analysis database containing 151 species from more than 200,000 forest plots spanning 4,000,000 square kilometers. We found that most species experienced conspecific negative density dependence (CNDD), but there was little effect of heterospecific density. Additionally, abundant species exhibited weaker CNDD than rarer species, and species-rich regions exhibited stronger CNDD than species-poor regions. Collectively, our results provide evidence that CNDD is a pervasive mechanism driving diversity across a gradient from boreal to subtropical forests.

In principle, the spin-½ plutonium-239 ((239)Pu) nucleus should be active in nuclear magnetic resonance spectroscopy. However, its signal has eluded detection for the past 50 years. Here, we report observation of a (239)Pu resonance from a solid sample of plutonium dioxide (PuO(2)) subjected to a wide scan of external magnetic field values (3 to 8 tesla) at a temperature of 4 kelvin. By mapping the external field dependence of the measured resonance frequency, we determined the nuclear gyromagnetic ratio (239)γ(n)(PuO(2))/2π to be 2.856 ± 0.001 megahertz per tesla (MHz/T). Assuming a free-ion value for the Pu(4+) hyperfine coupling constant, we estimated a bare (239)γ(n)/2π value of ~2.29 MHz/T, corresponding to a nuclear magnetic moment of μ(n) ≈ 0.15μ(N)(where μ(N) is the nuclear magneton).

Theory predicts the water hexamer to be the smallest water cluster with a three-dimensional hydrogen-bonding network as its minimum energy structure. There are several possible low-energy isomers, and calculations with different methods and basis sets assign them different relative stabilities. Previous experimental work has provided evidence for the cage, book, and cyclic isomers, but no experiment has identified multiple coexisting structures. Here, we report that broadband rotational spectroscopy in a pulsed supersonic expansion unambiguously identifies all three isomers; we determined their oxygen framework structures by means of oxygen-18-substituted water (H(2)(18)O). Relative isomer populations at different expansion conditions establish that the cage isomer is the minimum energy structure. Rotational spectra consistent with predicted heptamer and nonamer structures have also been identified.

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.

Calcium uptake into mitochondria occurs via a recently identified ion channel called the uniporter. Here, we characterize the phylogenomic distribution of the uniporter's membrane-spanning pore subunit (MCU) and regulatory partner (MICU1). Homologs of both components tend to co-occur in all major branches of eukaryotic life, but both have been lost along certain protozoan and fungal lineages. Several bacterial genomes also contain putative MCU homologs that may represent prokaryotic calcium channels. The analyses indicate that the uniporter may have been an early feature of mitochondria.

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.

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.

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.

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.

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.

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.

Over the second half of the 20th century, conflicts within national boundaries became increasingly dominant. One-third of all countries experienced civil conflict. Many (if not most) such conflicts involved violence along ethnic lines. On the basis of recent theoretical and empirical research, we provide evidence that preexisting ethnic divisions do influence social conflict. Our analysis also points to particular channels of influence. Specifically, we show that two different measures of ethnic division-polarization and fractionalization-jointly influence conflict, the former more so when the winners enjoy a "public" prize (such as political power or religious hegemony), the latter more so when the prize is "private"(such as looted resources, government subsidies, or infrastructures). The available data appear to strongly support existing theories of intergroup conflict. Our argument also provides indirect evidence that ethnic conflicts are likely to be instrumental, rather than driven by primordial hatreds.

Religion, in promoting outlandish beliefs and costly rituals, increases ingroup trust but also may increase mistrust and conflict with outgroups. Moralizing gods emerged over the last few millennia, enabling large-scale cooperation, and sociopolitical conquest even without war. Whether for cooperation or conflict, sacred values, like devotion to God or a collective cause, signal group identity and operate as moral imperatives that inspire nonrational exertions independent of likely outcomes. In conflict situations, otherwise mundane sociopolitical preferences may become sacred values, acquiring immunity to material incentives. Sacred values sustain intractable conflicts that defy "business-like" negotiation, but also provide surprising opportunities for resolution.

Humans have an evolved propensity to think categorically about social groups. This propensity is manifest in cognitive processes that have broad implications for public and political endorsement of multicultural policy. Drawing on these principles, we postulate a cognitive-evolutionary account of human adaptation to social diversity. This account explains broad social trends marking a resistance to multiculturalism, while providing an important reorienting call for scholars and policy-makers seeking intervention-based solutions to the problem of prejudice.

Although people often tend to consider themselves and others as unique individuals, there are many situations in which they think, feel, and act primarily as group members. This can bring out the best in them, as when they are inspired to help fellow citizens in need, or the worst, as when they show hostility against others simply because they represent another religious or ethnic group. Understanding when and why the group self becomes more important than the individual self, and how this affects people's thoughts, feelings, and behaviors, can help to prevent and redirect unwelcome aspects of human behavior by addressing them at the appropriate level of self.