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Journal: Science advances


We report the discovery that strains ofStaphylococcus epidermidisproduce 6-N-hydroxyaminopurine (6-HAP), a molecule that inhibits DNA polymerase activity. In culture, 6-HAP selectively inhibited proliferation of tumor lines but did not inhibit primary keratinocytes. Resistance to 6-HAP was associated with the expression of mitochondrial amidoxime reducing components, enzymes that were not observed in cells sensitive to this compound. Intravenous injection of 6-HAP in mice suppressed the growth of B16F10 melanoma without evidence of systemic toxicity. Colonization of mice with anS. epidermidisstrain producing 6-HAP reduced the incidence of ultraviolet-induced tumors compared to mice colonized by a control strain that did not produce 6-HAP.S. epidermidisstrains producing 6-HAP were found in the metagenome from multiple healthy human subjects, suggesting that the microbiome of some individuals may confer protection against skin cancer. These findings show a new role for skin commensal bacteria in host defense.

Concepts: DNA, Cancer, Bacteria, Adenosine triphosphate, Enzyme, Tumor, Neoplasm, DNA polymerase I


Ediacaran trace fossils provide key paleontological evidence for the evolution of early animals and their behaviors. Thus far, however, this fossil record has been limited to simple surface trails and relatively shallow burrows. We report possible trackways, preserved in association with burrows, from the terminal Ediacaran Shibantan Member (ca. 551 to ca. 541 million years ago) in the Yangtze Gorges area of South China. These trace fossils represent the earliest known trackways. They consist of two rows of imprints arranged in poorly organized series or repeated groups. These trackways may have been produced by bilaterian animals with paired appendages, although the phylum-level phylogenetic affinity of the trace makers remains unknown. It is possible that the trackways and associated burrows were produced by the same trace maker, indicating a complex behavior involving both walking and burrowing. Together, these trackways and burrows mark the arrival of a new era characterized by an increasing geobiological footprint of bilaterian animals.


The risk associated with any climate change impact reflects intensity of natural hazard and level of human vulnerability. Previous work has shown that a wet-bulb temperature of 35°C can be considered an upper limit on human survivability. On the basis of an ensemble of high-resolution climate change simulations, we project that extremes of wet-bulb temperature in South Asia are likely to approach and, in a few locations, exceed this critical threshold by the late 21st century under the business-as-usual scenario of future greenhouse gas emissions. The most intense hazard from extreme future heat waves is concentrated around densely populated agricultural regions of the Ganges and Indus river basins. Climate change, without mitigation, presents a serious and unique risk in South Asia, a region inhabited by about one-fifth of the global human population, due to an unprecedented combination of severe natural hazard and acute vulnerability.

Concepts: Population, Earth, Climate change, Population density, India, Natural gas, World population, Greenhouse gas


The intensification of agriculture is often associated with declining mobility and bone strength through time, although women often exhibit less pronounced trends than men. For example, previous studies of prehistoric Central European agriculturalists (~5300 calibrated years BC to 850 AD) demonstrated a significant reduction in tibial rigidity among men, whereas women were characterized by low tibial rigidity, little temporal change, and high variability. Because of the potential for sex-specific skeletal responses to mechanical loading and a lack of modern comparative data, women’s activity in prehistory remains difficult to interpret. This study compares humeral and tibial cross-sectional rigidity, shape, and interlimb loading among prehistoric Central European women agriculturalists and living European women of known behavior (athletes and controls). Prehistoric female tibial rigidity at all time periods was highly variable, but differed little from living sedentary women on average, and was significantly lower than that of living runners and football players. However, humeral rigidity exceeded that of living athletes for the first ~5500 years of farming, with loading intensity biased heavily toward the upper limb. Interlimb strength proportions among Neolithic, Bronze Age, and Iron Age women were most similar to those of living semi-elite rowers. These results suggest that, in contrast to men, rigorous manual labor was a more important component of prehistoric women’s behavior than was terrestrial mobility through thousands of years of European agriculture, at levels far exceeding those of modern women.

Concepts: Europe, Slovakia, Germany, Stone Age, Hungary, Bronze Age, Synoptic table of the principal old world prehistoric cultures, Three-age system


We present the first known fossilized snake embryo/neonate preserved in early Late Cretaceous (Early Cenomanian) amber from Myanmar, which at the time, was an island arc including terranes from Austral Gondwana. This unique and very tiny snake fossil is an articulated postcranial skeleton, which includes posterior precloacal, cloacal, and caudal vertebrae, and details of squamation and body shape; a second specimen preserves a fragment of shed skin interpreted as a snake. Important details of skeletal ontogeny, including the stage at which snake zygosphene-zygantral joints began to form along with the neural arch lamina, are preserved. The vertebrae show similarities to those of fossil Gondwanan snakes, suggesting a dispersal route of Gondwanan faunas to Laurasia. Finally, the new species is the first Mesozoic snake to be found in a forested environment, indicating greater ecological diversity among early snakes than previously thought.


On the basis of an assemblage of fossilized wing scales recovered from latest Triassic and earliest Jurassic sediments from northern Germany, we provide the earliest evidence for Lepidoptera (moths and butterflies). The diverse scales confirm a (Late) Triassic radiation of lepidopteran lineages, including the divergence of the Glossata, the clade that comprises the vast multitude of extant moths and butterflies that have a sucking proboscis. The microfossils extend the minimum calibrated age of glossatan moths by ca. 70 million years, refuting ancestral association of the group with flowering plants. Development of the proboscis may be regarded as an adaptive innovation to sucking free liquids for maintaining the insect’s water balance under arid conditions. Pollination drops secreted by a variety of Mesozoic gymnosperms may have been non-mutualistically exploited as a high-energy liquid source. The early evolution of the Lepidoptera was probably not severely interrupted by the end-Triassic biotic crisis.

Concepts: Insect, Water, Lepidoptera, Moth, Butterfly, Dinosaur, Triassic, Cycad


Extreme events such as heat waves are among the most challenging aspects of climate change for societies. We show that climate models consistently project increases in temperature variability in tropical countries over the coming decades, with the Amazon as a particular hotspot of concern. During the season with maximum insolation, temperature variability increases by ~15% per degree of global warming in Amazonia and Southern Africa and by up to 10%°C-1 in the Sahel, India, and Southeast Asia. Mechanisms include drying soils and shifts in atmospheric structure. Outside the tropics, temperature variability is projected to decrease on average because of a reduced meridional temperature gradient and sea-ice loss. The countries that have contributed least to climate change, and are most vulnerable to extreme events, are projected to experience the strongest increase in variability. These changes would therefore amplify the inequality associated with the impacts of a changing climate.


The exact timing, route, and process of the initial peopling of the Americas remains uncertain despite much research. Archaeological evidence indicates the presence of humans as far as southern Chile by 14.6 thousand years ago (ka), shortly after the Pleistocene ice sheets blocking access from eastern Beringia began to retreat. Genetic estimates of the timing and route of entry have been constrained by the lack of suitable calibration points and low genetic diversity of Native Americans. We sequenced 92 whole mitochondrial genomes from pre-Columbian South American skeletons dating from 8.6 to 0.5 ka, allowing a detailed, temporally calibrated reconstruction of the peopling of the Americas in a Bayesian coalescent analysis. The data suggest that a small population entered the Americas via a coastal route around 16.0 ka, following previous isolation in eastern Beringia for ~2.4 to 9 thousand years after separation from eastern Siberian populations. Following a rapid movement throughout the Americas, limited gene flow in South America resulted in a marked phylogeographic structure of populations, which persisted through time. All of the ancient mitochondrial lineages detected in this study were absent from modern data sets, suggesting a high extinction rate. To investigate this further, we applied a novel principal components multiple logistic regression test to Bayesian serial coalescent simulations. The analysis supported a scenario in which European colonization caused a substantial loss of pre-Columbian lineages.

Concepts: DNA, Regression analysis, United States, Brazil, South America, Americas, Latin America, Indigenous peoples of the Americas


Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. We omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. We find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the Proterozoic and Phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water, which, for an exoplanet twin, may be remotely detectable. On the basis of this disequilibrium, we argue that the simultaneous detection of abundant CH4 and CO2 in a habitable exoplanet’s atmosphere is a potential biosignature. Specifically, we show that methane mixing ratios greater than 10-3 are potentially biogenic, whereas those exceeding 10-2 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario.

Concepts: Water, Solar System, Planet, Mars, Atmosphere, Neptune, Uranus, Proterozoic


Establishing the age of the Moon is critical to understanding solar system evolution and the formation of rocky planets, including Earth. However, despite its importance, the age of the Moon has never been accurately determined. We present uranium-lead dating of Apollo 14 zircon fragments that yield highly precise, concordant ages, demonstrating that they are robust against postcrystallization isotopic disturbances. Hafnium isotopic analyses of the same fragments show extremely low initial (176)Hf/(177)Hf ratios corrected for cosmic ray exposure that are near the solar system initial value. Our data indicate differentiation of the lunar crust by 4.51 billion years, indicating the formation of the Moon within the first ~60 million years after the birth of the solar system.

Concepts: Earth, Sun, Solar System, Moon, Dwarf planet, Venus, Io, Impact crater