Archive for the ‘Proceedings of the National Academy of Sciences’ Category

Social disadvantage, genetic sensitivity, and children’s telomere length

April 11, 2014 Comments off

Social disadvantage, genetic sensitivity, and children’s telomere length (PDF)
Source: Proceedings of the National Academy of Sciences

This paper makes two contributions to research on the link between the social environment and health. Using data from a birth cohort study, we show that, among African American boys, those who grow up in highly disadvantaged environments have shorter telomeres (at age 9) than boys who grow up in highly advantaged environments. We also find that the association between the social environment and telomere length (TL) is moderated by genetic variation within the serotonin and dopamine pathways. Boys with the highest genetic sensitivity scores had the shortest TL when exposed to disadvantaged environments and the longest TL when exposed to advantaged environments. To our knowledge, this report is the first to document a gene–social environment interaction for TL, a biomarker of stress exposure.

See: Stressful environments genetically affect African American boys (Science Daily)

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Increasing homogeneity in global food supplies and the implications for food security

April 1, 2014 Comments off

Increasing homogeneity in global food supplies and the implications for food security
SOurce: Proceedings of the National Academy of Sciences

The narrowing of diversity in crop species contributing to the world’s food supplies has been considered a potential threat to food security. However, changes in this diversity have not been quantified globally. We assess trends over the past 50 y in the richness, abundance, and composition of crop species in national food supplies worldwide. Over this period, national per capita food supplies expanded in total quantities of food calories, protein, fat, and weight, with increased proportions of those quantities sourcing from energy-dense foods. At the same time the number of measured crop commodities contributing to national food supplies increased, the relative contribution of these commodities within these supplies became more even, and the dominance of the most significant commodities decreased. As a consequence, national food supplies worldwide became more similar in composition, correlated particularly with an increased supply of a number of globally important cereal and oil crops, and a decline of other cereal, oil, and starchy root species. The increase in homogeneity worldwide portends the establishment of a global standard food supply, which is relatively species-rich in regard to measured crops at the national level, but species-poor globally. These changes in food supplies heighten interdependence among countries in regard to availability and access to these food sources and the genetic resources supporting their production, and give further urgency to nutrition development priorities aimed at bolstering food security.

Oxygen requirements of the earliest animals

March 24, 2014 Comments off

Oxygen requirements of the earliest animals
Source: Proceedings of the National Academy of Sciences

A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth’s surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850–542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635–542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5–4.0% present atmospheric levels. Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period. Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans. Instead, other ecological and developmental processes are needed to adequately explain the origin and earliest evolution of animal life on Earth.

Media’s role in broadcasting acute stress following the Boston Marathon bombings

February 18, 2014 Comments off

Media’s role in broadcasting acute stress following the Boston Marathon bombings
Source: Proceedings of the National Academy of Sciences

Media coverage of collective traumas may trigger psychological distress in individuals outside the directly affected community. We examined whether repeated media exposure to the Boston Marathon bombings was associated with acute stress and compared the impact of direct exposure (being at/near the bombings) vs. media exposure (bombing-related television, radio, print, online, and social media coverage) on acute stress. We conducted an Internet-based survey 2–4 wk postbombings with a nationally representative sample and representative subsamples from Boston and New York (4,675 adults). Repeated bombing-related media exposure was associated with higher acute stress than was direct exposure. Media coverage following collective traumas can diffuse acute stress widely. This unique study compares the impact of direct vs. indirect media-based community trauma exposure on acute stress responses.

Coastal flood damage and adaptation costs under 21st century sea-level rise

February 12, 2014 Comments off

Coastal flood damage and adaptation costs under 21st century sea-level rise
Source: Proceedings of the National Academy of Sciences

Coastal flood damages are expected to increase significantly during the 21st century as sea levels rise and socioeconomic development increases the number of people and value of assets in the coastal floodplain. Estimates of future damages and adaptation costs are essential for supporting efforts to reduce emissions driving sea-level rise as well as for designing strategies to adapt to increasing coastal flood risk. This paper presents such estimates derived by taking into account a wide range of uncertainties in socioeconomic development, sea-level rise, continental topography data, population data, and adaptation strategies.

Increasing socioeconomic disparities in adolescent obesity

February 6, 2014 Comments off

Increasing socioeconomic disparities in adolescent obesity
Source: Proceedings of the National Academy of Sciences

Childhood and youth obesity represent significant US public health challenges. Recent findings that the childhood obesity ‘‘epidemic’’ may have slightly abated have been met with relief from health professionals and popular media. However, we document that the overall trend in youth obesity rates masks a significant and growing class gap between youth from upper and lower socioeconomic status (SES) backgrounds. Until 2002, obesity rates increased at similar rates for all adolescents, but since then, obesity has begun to decline among higher SES youth but continued to increase among lower SES youth. These results underscore the need to target public health interventions to disadvantaged youth who remain at risk, as well as to examine how health information circulates through class-biased channels.

Evaluative and hedonic wellbeing among those with and without children at home

January 30, 2014 Comments off

Evaluative and hedonic wellbeing among those with and without children at home
Source: Proceedings of the National Academy of Sciences

We document and interpret differences in life evaluation and in hedonic experience between those who live with children and those who do not; most previous literature has concluded that those with children have worse lives. For a sample of 1.8 million Americans of all ages, and without controls for other circumstances, we find little difference in subjective wellbeing between people with and without children. Among those most likely to be parents, life evaluation and all hedonic experiences except stress are markedly better among those living with a child. However, within this group, people who live with children are more likely to be married, richer, better educated, more religious, and healthier, all of which have well-documented positive associations with evaluative and hedonic wellbeing. With statistical controls for these background factors, the presence of a child has a small negative association with life evaluation, although it is associated with more of both positive and negative hedonics. These patterns are replicated in the English-speaking countries of the world, but not in other regions. We argue that the causal effect of children on parental wellbeing, which is the target for most of the literature, is not well defined. Instead, we interpret our rich-country results within a theory of children and wellbeing in which adults sort into parenthood according to their preferences. In poor, high-fertility countries, we find evidence that at least some people have children even when it diminishes their personal wellbeing.

Small business activity does not measure entrepreneurship

January 23, 2014 Comments off

Small business activity does not measure entrepreneurship
Source: Proceedings of the National Academy of Sciences

Schumpeterian entrepreneurship refers to growing and innovative firms. However, in empirical research the rate of entrepreneurship is commonly estimated using the self-employment rate or other measures of small business activity. We argue that this empirical strategy gives rise to misleading inferences regarding Schumpeterian entrepreneurship. To unambiguously identify this type of entrepreneur we focus on self-made billionaires on Forbes Magazine’s list who became wealthy by founding new firms. We identify 996 such billionaire entrepreneurs in over 50 countries. The rate of billionaire entrepreneurs correlates negatively with self-employment, small business ownership, and startup rates. Countries with higher income, higher trust, lower taxes, more venture capital investment, and lower regulatory burdens have higher entrepreneurship rates but less self-employment.

Multimodel assessment of water scarcity under climate change

December 18, 2013 Comments off

Multimodel assessment of water scarcity under climate change
Source: Proceedings of the National Academy of Sciences

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.

Efficient discovery of overlapping communities in massive networks

December 3, 2013 Comments off

Efficient discovery of overlapping communities in massive networks
Source: Proceedings of the National Academy of Sciences

Detecting overlapping communities is essential to analyzing and exploring natural networks such as social networks, biological networks, and citation networks. However, most existing approaches do not scale to the size of networks that we regularly observe in the real world. In this paper, we develop a scalable approach to community detection that discovers overlapping communities in massive real-world networks. Our approach is based on a Bayesian model of networks that allows nodes to participate in multiple communities, and a corresponding algorithm that naturally interleaves subsampling from the network and updating an estimate of its communities. We demonstrate how we can discover the hidden community structure of several real-world networks, including 3.7 million US patents, 575,000 physics articles from the arXiv preprint server, and 875,000 connected Web pages from the Internet. Furthermore, we demonstrate on large simulated networks that our algorithm accurately discovers the true community structure. This paper opens the door to using sophisticated statistical models to analyze massive networks.

Measurements of methane emissions at natural gas production sites in the United States

December 2, 2013 Comments off

Measurements of methane emissions at natural gas production sites in the United States
Source: Proceedings of the National Academy of Sciences

This work reports direct measurements of methane emissions at 190 onshore natural gas sites in the United States. The measurements indicate that well completion emissions are lower than previously estimated; the data also show emissions from pneumatic controllers and equipment leaks are higher than Environmental Protection Agency (EPA) national emission projections. Estimates of total emissions are similar to the most recent EPA national inventory of methane emissions from natural gas production. These measurements will help inform policymakers, researchers, and industry, providing information about some of the sources of methane emissions from the production of natural gas, and will better inform and advance national and international scientific and policy discussions with respect to natural gas development and use.

Excitable human dynamics driven by extrinsic events in massive communities

October 8, 2013 Comments off

Excitable human dynamics driven by extrinsic events in massive communities
Source: Proceedings of the National Academy of Sciences

Online social networks have over the last decade influenced the way people interact. Data from Twitter allow for a detailed study of the activity in online massive communities. By studying the frequency by which international brands appear on Twitter and the trade of financial securities on financial markets, we find a characteristic bursty behavior of the activity levels of Twitter users and market participants. We explain the bursty behavior by a simple model of the large-scale human behavior and quantify the correlations in the activity levels. The statistical similarity of the two social systems is an indication that the complex process underlying individual decision-making might not be very different for Twitter users and participants in financial markets.

See: Explosive Dynamic Behavior On Twitter and in the Financial Market (Science Daily)

Model projections of atmospheric steering of Sandy-like superstorms

September 30, 2013 Comments off

Model projections of atmospheric steering of Sandy-like superstorms
Source: Proceedings of the National Academy of Sciences

Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multimodel ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast.

US studies may overestimate effect sizes in softer research

September 24, 2013 Comments off

US studies may overestimate effect sizes in softer research
Source: Proceedings of the National Academy of Sciences

Many biases affect scientific research, causing a waste of resources, posing a threat to human health, and hampering scientific progress. These problems are hypothesized to be worsened by lack of consensus on theories and methods, by selective publication processes, and by career systems too heavily oriented toward productivity, such as those adopted in the United States (US). Here, we extracted 1,174 primary outcomes appearing in 82 meta-analyses published in health-related biological and behavioral research sampled from the Web of Science categories Genetics & Heredity and Psychiatry and measured how individual results deviated from the overall summary effect size within their respective meta-analysis. We found that primary studies whose outcome included behavioral parameters were generally more likely to report extreme effects, and those with a corresponding author based in the US were more likely to deviate in the direction predicted by their experimental hypotheses, particularly when their outcome did not include additional biological parameters. Nonbehavioral studies showed no such “US effect” and were subject mainly to sampling variance and small-study effects, which were stronger for non-US countries. Although this latter finding could be interpreted as a publication bias against non-US authors, the US effect observed in behavioral research is unlikely to be generated by editorial biases. Behavioral studies have lower methodological consensus and higher noise, making US researchers potentially more likely to express an underlying propensity to report strong and significant findings.

Predicting the public health benefit of vaccinating cattle against Escherichia coli O157

September 18, 2013 Comments off

Predicting the public health benefit of vaccinating cattle against Escherichia coli O157
Source: Proceedings of the National Academy of Sciences

Identifying the major sources of risk in disease transmission is key to designing effective controls. However, understanding of transmission dynamics across species boundaries is typically poor, making the design and evaluation of controls particularly challenging for zoonotic pathogens. One such global pathogen is Escherichia coli O157, which causes a serious and sometimes fatal gastrointestinal illness. Cattle are the main reservoir for E. coli O157, and vaccines for cattle now exist. However, adoption of vaccines is being delayed by conflicting responsibilities of veterinary and public health agencies, economic drivers, and because clinical trials cannot easily test interventions across species boundaries, lack of information on the public health benefits. Here, we examine transmission risk across the cattle–human species boundary and show three key results. First, supershedding of the pathogen by cattle is associated with the genetic marker stx2. Second, by quantifying the link between shedding density in cattle and human risk, we show that only the relatively rare supershedding events contribute significantly to human risk. Third, we show that this finding has profound consequences for the public health benefits of the cattle vaccine. A naïve evaluation based on efficacy in cattle would suggest a 50% reduction in risk; however, because the vaccine targets the major source of human risk, we predict a reduction in human cases of nearly 85%. By accounting for nonlinearities in transmission across the human–animal interface, we show that adoption of these vaccines by the livestock industry could prevent substantial numbers of human E. coli O157 cases.

Human development of the ability to learn from bad news

September 11, 2013 Comments off

Human development of the ability to learn from bad news
Source: Proceedings of the National Academy of Sciences

Humans show a natural tendency to discount bad news while incorporating good news into beliefs (the “good news–bad news effect”), an effect that may help explain seemingly irrational risk taking. Understanding how this bias develops with age is important because adolescents are prone to engage in risky behavior; thus, educating them about danger is crucial. We reveal a striking valence-dependent asymmetry in how belief updating develops with age. In the ages tested (9–26 y), younger age was associated with inaccurate updating of beliefs in response to undesirable information regarding vulnerability. In contrast, the ability to update beliefs accurately in response to desirable information remained relatively stable with age. This asymmetry was mediated by adequate computational use of positive but not negative estimation errors to alter beliefs. The results are important for understanding how belief formation develops and might help explain why adolescents do not respond adequately to warnings.

The Great Recession, genetic sensitivity, and maternal harsh parenting

August 19, 2013 Comments off

The Great Recession, genetic sensitivity, and maternal harsh parenting (PDF)
Source: Proceedings of the National Academy of Sciences

Using data from the Fragile Families and Child Wellbeing Study, this study examined the effects of the Great Recession on maternal harsh parenting. We found that changes in macroeco- nomic conditions, rather than current conditions, affected harsh parenting, that declines in macroeconomic conditions had a stronger impact on harsh parenting than improvements in conditions, and that mothers’ responses to adverse economic conditions were moderated by the DRD2 Taq1A genotype. We found no evidence of a moderating effect for two other, less well-studied SNPs from the DRD4 and DAT1 genes.

Core foundations of abstract geometry

August 13, 2013 Comments off

Core foundations of abstract geometry
Source: Proceedings of the National Academy of Sciences

Human adults from diverse cultures share intuitions about the points, lines, and figures of Euclidean geometry. Do children develop these intuitions by drawing on phylogenetically ancient and developmentally precocious geometric representations that guide their navigation and their analysis of object shape? In what way might these early-arising representations support later-developing Euclidean intuitions? To approach these questions, we investigated the relations among young children’s use of geometry in tasks assessing: navigation; visual form analysis; and the interpretation of symbolic, purely geometric maps. Children’s navigation depended on the distance and directional relations of the surface layout and predicted their use of a symbolic map with targets designated by surface distances. In contrast, children’s analysis of visual forms depended on the size-invariant shape relations of objects and predicted their use of the same map but with targets designated by corner angles. Even though the two map tasks used identical instructions and map displays, children’s performance on these tasks showed no evidence of integrated representations of distance and angle. Instead, young children flexibly recruited geometric representations of either navigable layouts or objects to interpret the same spatial symbols. These findings reveal a link between the early-arising geometric representations that humans share with diverse animals and the flexible geometric intuitions that give rise to human knowledge at its highest reaches. Although young children do not appear to integrate core geometric representations, children’s use of the abstract geometry in spatial symbols such as maps may provide the earliest clues to the later construction of Euclidean geometry.

Global patterns of terrestrial vertebrate diversity and conservation

June 28, 2013 Comments off

Global patterns of terrestrial vertebrate diversity and conservation
Source: Proceedings of the National Academy of Sciences

Identifying priority areas for biodiversity is essential for directing conservation resources. Fundamentally, we must know where individual species live, which ones are vulnerable, where human actions threaten them, and their levels of protection. As conservation knowledge and threats change, we must reevaluate priorities. We mapped priority areas for vertebrates using newly updated data on >21,000 species of mammals, amphibians, and birds. For each taxon, we identified centers of richness for all species, small-ranged species, and threatened species listed with the International Union for the Conservation of Nature. Importantly, all analyses were at a spatial grain of 10 × 10 km, 100 times finer than previous assessments. This fine scale is a significant methodological improvement, because it brings mapping to scales comparable with regional decisions on where to place protected areas. We also mapped recent species discoveries, because they suggest where as-yet-unknown species might be living. To assess the protection of the priority areas, we calculated the percentage of priority areas within protected areas using the latest data from the World Database of Protected Areas, providing a snapshot of how well the planet’s protected area system encompasses vertebrate biodiversity. Although the priority areas do have more protection than the global average, the level of protection still is insufficient given the importance of these areas for preventing vertebrate extinctions. We also found substantial differences between our identified vertebrate priorities and the leading map of global conservation priorities, the biodiversity hotspots. Our findings suggest a need to reassess the global allocation of conservation resources to reflect today’s improved knowledge of biodiversity and conservation.

See: Mapping out How to Save Species (Science Daily)

Numerical ability predicts mortgage default

June 27, 2013 Comments off

Numerical ability predicts mortgage default
Source: Proceedings of the National Academy of Sciences

Unprecedented levels of US subprime mortgage defaults precipitated a severe global financial crisis in late 2008, plunging much of the industrialized world into a deep recession. However, the fundamental reasons for why US mortgages defaulted at such spectacular rates remain largely unknown. This paper presents empirical evidence showing that the ability to perform basic mathematical calculations is negatively associated with the propensity to default on one’s mortgage. We measure several aspects of financial literacy and cognitive ability in a survey of subprime mortgage borrowers who took out loans in 2006 and 2007, and match them to objective, detailed administrative data on mortgage characteristics and payment histories. The relationship between numerical ability and mortgage default is robust to controlling for a broad set of sociodemographic variables, and is not driven by other aspects of cognitive ability. We find no support for the hypothesis that numerical ability impacts mortgage outcomes through the choice of the mortgage contract. Rather, our results suggest that individuals with limited numerical ability default on their mortgage due to behavior unrelated to the initial choice of their mortgage.


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