THEY ARE TRYING TO PROVE THAT DARK MATTER/DARK ENERGY EXISTS
LIKE THE THEOREM OF THE AETHER BEFORE IT 

NEWS AND VIEWS
24 APRIL 2019

Dark-matter detector observes exotic nuclear decay

A detector that was designed to probe dark matter, the ‘missing’ mass in the Universe, has seen an elusive nuclear decay called two-neutrino double electron capture — with implications for nuclear and particle physics.

Jouni Suhonen

For half a century, our view of the world has been based on the standard model of particle physics. However, this view has been challenged by theories1 that can overcome some of the limitations of the standard model. These theories allow neutrinos to be Majorana particles (that is, they are indistinguishable from their own antiparticles) and predict the existence of weakly interacting massive particles (WIMPs) as the constituents of invisible ‘dark matter’ in the Universe. Majorana neutrinos mediate a type of nuclear decay called neutrinoless double-β decay, an example of which is neutrinoless double electron capture. A crucial step towards observing this decay is to detect its standard-model equivalent: two-neutrino double electron capture. In a paper in Nature, the XENON Collaboration2 reports the first direct observation of this process in xenon-124 nuclei, using a detector that was built to detect WIMPs.


Read the paper: Observation of two-neutrino double electron capture in 124Xe with XENON1T

All known interactions in the Universe are mediated by one of four forces: electromagnetic, gravitational, strong or weak. The electromagnetic force and gravitational force, which we encounter in daily life, are long-range and can act over large distances. The strong force acts over short distances and binds together elementary particles known as quarks to form nucleons (protons and neutrons) on the femtometre scale (1 fm is 10–15 m). The weaker long-range residue of the strong force, in turn, binds nucleons into atomic nuclei. For example, this residue binds together the 124 nucleons (54 protons and 70 neutrons) of a xenon-124 nucleus. Last, the weak force is extremely short-range and causes atomic nuclei to disintegrate through a process called nuclear β-decay.

One type of β-decay is nuclear electron capture, in which a nucleus, embedded in an atom, captures an electron from the electron shells that surround it (Fig. 1a). As a result, one proton in the nucleus is converted into a neutron, and a neutrino is emitted. Electron capture, or any other form of β-decay, is known as a lowest-order weak interaction. For such processes, the decay rate of a nucleus, which is inversely proportional to the half-life of the nucleus, is proportional to the square of the weak coupling constant — a parameter that quantifies the strength of the weak force. Because this constant is small, the resulting half-life is long. For example, in the case of the electron-capture-mediated decay of iodine-124 to tellurium-124, the half-life is 4.2 days.


Figure 1 | Electron capture and two-neutrino double electron capture. a, An iodine-124 atom can decay with a half-life of 4.2 days to an atom of tellurium-124, through a process called electron capture. The nucleus of the iodine-124 atom captures an electron from the electron shells that surround it. A proton (circled) in the nucleus is converted into a neutron, and a neutrino is emitted. b, A xenon-124 atom cannot decay by electron capture, because of the law of energy conservation. However, it can decay with an extremely long half-life to a tellurium-124 atom, through a process known as two-neutrino double electron capture. The xenon-124 nucleus captures two electrons from the surrounding electron shells, which results in the conversion of two protons (circled) into neutrons, and the emission of two neutrinos. The XENON Collaboration2 has measured the half-life of this process to be 1.8 × 1022 years — about one trillion times the age of the Universe.

In some instances, electron capture (or any other lowest-order weak interaction) is forbidden by the law of energy conservation. Then, the nuclear decay can proceed through a weak-interaction process of the second order, for which the decay rate is proportional to the fourth power of the weak coupling constant, and the associated half-life is extremely long. An example of a second-order weak interaction is two-neutrino double electron capture, in which a nucleus captures two electrons from the electron shells that surround it, resulting in the conversion of two protons into neutrons and the emission of two neutrinos (Fig. 1b).

This process can be viewed as two simultaneous electron-capture decays that directly convert an atomic nucleus into one that has two fewer protons and two more neutrons. Each captured electron leaves a hole in the electron shell from which it came. These holes are filled by other atomic electrons, leading to the emission of X-rays and electrons called Auger electrons. Such emissions pave the way for the direct observation of two-neutrino double electron capture in a nucleus. The first experimental indications of this process were obtained for krypton-78 in direct counting experiments3,4, in which the double electron captures are registered one by one, and for barium-130 in geochemical studies5,6.

The XENON Collaboration looked for the decay of xenon-124 to tellurium-124, which occurs through two-neutrino double electron capture, using the XENON1T dark-matter detector. This instrument contains about 3 tonnes of ultra-pure liquid xenon and was designed to search for the scattering of WIMPs off xenon nuclei7. The detector is at the Gran Sasso National Laboratory, which is located under the Gran Sasso massif in central Italy, roughly 120 km from Rome. The researchers carried out a direct counting experiment in which emissions of X-rays and Auger electrons were measured to pin down the rare decay. The data were collected over one year (between 2017 and 2018) as part of the hunt for WIMPs.

Thanks to the huge amount of xenon in the detector, the authors achieved the first direct observation of two-neutrino double electron capture in xenon-124 nuclei. They measured the half-life of the process to be 1.8 × 1022 years, which is about one trillion times the age of the Universe. The successful measurement of this half-life lays the foundations for experiments that aim to detect these rare decays in other nuclei. Moreover, the researchers’ use of a WIMP-searching liquid-xenon instrument provides striking evidence of the power and versatility of such detectors. However, only four types of double-β decay can be probed by these instruments — namely, the decays of xenon-124, xenon-126, xenon-134 and xenon-136.

From the point of view of nuclear theory, the decay rates of both two-neutrino and neutrinoless double electron capture can be connected to quantities called nuclear matrix elements. Such quantities contain information about nuclear structure that is extracted from nuclear models and can be applied by researchers in the field of nuclear-structure theory. The measured two-neutrino double electron capture will help to test the various nuclear models8 that are used to calculate rates of double-β decay. Moreover, the acquired half-life data will enable model parameters to be fine-tuned, allowing scientists to more accurately predict the values of the nuclear matrix elements that are associated with neutrinoless double electron capture, as well as neutrinoless double-β decays in general. Finally, all of these factors will contribute to the accurate extraction of neutrino parameters from the data gathered by present and future neutrino experiments.

Nature 568, 462-463 (2019)
doi: 10.1038/d41586-019-01212-8

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Sea animals are more vulnerable to warming than are land ones
NEWS AND VIEWS
25 APRIL 2019Anthony J. Richardson & David S. Schoeman
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The impact of climate change on biodiversity is a pressing concern. A study now combines experimental data with careful modelling to compare the vulnerability to warming of animal species on land and in the ocean.

Ecologists, conservationists and policymakers are struggling to understand how much of a threat climate change poses to Earth’s biodiversity — estimated to be some 3 million to 100 million species1 — and what to do about that threat. Knowing whether terrestrial or marine species are more vulnerable to climate change, as well as how the risks vary with latitude, could inform the deployment of limited conservation resources, nationally and globally. Writing in Nature, Pinsky et al.2combine robust experimental data with a careful model-based approach to compare the vulnerability of biodiversity to warming across latitudes on land and in the ocean.


Read the paper: Greater vulnerability to warming of marine versus terrestrial ectotherms

There is contradictory evidence about the relative vulnerability to warming of land and ocean animals. Terrestrial species could be at greater risk because they are less able to adapt to new climatic conditions3 and because they are exposed to higher extreme temperatures than are ocean-dwelling species. But marine species could be more affected because temperature strongly controls their geographic limits4, nutrient supplies5 and oxygen availability6.

Temperature extremes, rather than average temperatures, are an important determinant of population survival at the warm edge of a species’ temperature range7. Guided by this evidence, Pinsky et al. calculated the thermal safety margin — defined as the difference between the highest temperature at which an animal can survive (its maximum thermal tolerance) and the maximum body temperature that it will effectively experience under natural conditions — for 387 species of ectothermic animal, which rely on external heat to maintain body temperature. The authors calculated two versions of the thermal safety margin for each species: one for when the animal is fully exposed to heat and one for when it is in a thermal refuge. Terrestrial thermal refuges include microclimates such as shade under a tree or rock, whereas marine thermal refuges comprise deeper, cooler waters.

Pinsky et al. found that there are no thermal safety margins for land-dwelling ectotherms when they have no access to thermal refuges, whereas such margins exist for their ocean-dwelling counterparts. This suggests that land species might be more at risk from climate change than ocean species are. However, when thermal refuges were taken into account, the situation was reversed, with the thermal safety margins being broader for species on land than for those in the ocean (Fig. 1). This implies that marine species might actually be more at risk.


Figure 1 | Thermal safety margins for land and ocean animals that can access thermal refuges. Pinsky et al.2 calculated the thermal safety margin — defined as the difference between the maximum temperature that a species can tolerate and the maximum temperature that it will experience — for 387 ectothermic animal species, which rely on external heat to maintain their body temperature. The authors took into account the ability of animals to access thermal refuges, which are areas in their habitat where they can cool down. Individual data points for different types of animal and solid lines show the present conditions, whereas dashed lines are an estimate of the situation in the year 2100 under the representative concentration pathway 8.5 (RCP8.5) scenario of predicted greenhouse-gas concentration trajectories. The narrower, in general, thermal safety margins in the ocean suggest that warming poses a greater risk to marine species than to those that live on land. (Adapted from Pinsky et al.)

The authors went on to observe that, when thermal refuges were considered, the thermal safety margins of land species were narrowest at the subtropics and widened towards the tropics and poles (Fig. 1), which suggests that warming is a greater threat to subtropical species than to species living in other regions. But, under the same consideration, the thermal safety margins of ocean species were narrowest at the tropics and widened towards the poles, which implies that tropical species are at greater risk from warming. The authors project that with future climate change, terrestrial species in general will continue to have wider thermal safety margins than marine species, but that subtropical terrestrial species will have thermal safety margins as narrow as those of their marine counterparts.

This work has several implications for biodiversity and conservation. First, it predicts that tropical marine species will be most vulnerable to climate change, as they have the narrowest thermal safety margins of all groups of species analysed. The threat to tropical marine species is exacerbated by the predicted replacement of the present highest ocean temperatures by even higher ones, which would cause a rapid poleward shift of the thermal habitat of such species8.

Second, the findings highlight the essential role of thermal refuges in maintaining reasonable thermal safety margins for land animals. The authors observed that the maximum temperature that such animals can tolerate is remarkably flat between the latitudes of 50° N and 50° S. Therefore, variation in thermal safety margins with latitude is largely dictated by the degree of heat to which land animals are exposed in thermal refuges. Intact environments, with trees for shade and accessible water for evaporative cooling, will be crucial for the persistence of terrestrial species in a warming world.

Last, the latitudinal pattern of thermal safety margins suggests that marine species moving north or south from the Equator to escape the warmest environments as they become too hot will typically encounter widening thermal safety margins. This will potentially decrease the vulnerability of such species to temperature extremes. By contrast, land-dwelling tropical species moving polewards as the result of a warming climate might have to run the gauntlet of narrow thermal safety margins in the subtropics (caused by high thermal extremes in these regions) before the margins widen again at higher latitudes. This potentially places terrestrial tropical species at great risk.

Despite the authors’ careful analysis, their work has several limitations, which provide avenues for future research. Pinsky et al. used the best available data, but collecting further data would boost confidence in their findings. Information on the maximum thermal tolerance was available for only a small number of species from a few phyla. Most of the species (318 of the 406 species considered in some parts of the analysis) were terrestrial, and insect biodiversity was severely under-represented. And because the majority of the 88 marine species analysed were fish, information on ocean invertebrate biodiversity was largely missing.

Only 7% of the marine species included in the study were pelagic (living in the water column), meaning that they can seek refuge in deeper, cooler waters when the temperature rises. The remaining 93% of marine species analysed were demersal (living on or near the bottom of the ocean), and so their ability to access thermal refuges is limited. Because pelagic species can access cooler waters, their thermal safety margins are probably greater than those of demersal species. Therefore, the reported differences between terrestrial and marine animals might be better framed as differences between terrestrial species, which are able to access thermal refuges, and demersal marine species, which are not. More work to determine the maximum thermal tolerance of pelagic species is clearly needed.

It is also evident that we have a more sophisticated understanding of thermal refuges on land than in the ocean. Pinsky et al. used several theoretical models to describe the impact of terrestrial microclimates on an animal’s body temperature. There is no similar theoretical framework for marine species and their habitats, so the authors had to make coarser assumptions about how body temperature decreases in thermal refuges. This imbalance in our understanding of land and ocean thermal refuges should be addressed by future studies.

Even using the terms microhabitat or microclimate in the context of marine animals might be misleading because the cooler area below the warm top 200 metres of the ocean is the largest habitat on Earth and has a fairly uniform temperature. The idea that most marine ectotherms spend time in deep waters to offset warm surface conditions might also not be true, because many animals that live in the middle layers of the water column (200–1,000 metres below the surface), such as tuna, spend time close to the ocean surface to warm up9.

The vulnerability of biodiversity to warming is an active area of investigation, and Pinsky et al. have provided valuable insights that will stimulate further research. Their approach could also be used to investigate the vulnerability of biodiversity to other aspects of climate change — including rainfall or pH change — whose extremes might affect species and whose impact might be buffered by refuges.



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A closer look at lightning reveals needle-like structures

NATURE NEWS AND VIEWS
17 APRIL 2019

Structural features have been identified on positively charged lightning channels that are not present on negatively charged ones. The discovery could explain why these two types of channel have different behaviours.

Earle Williams & Joan Montanyà

Accelerated electric charge in lightning produces electromagnetic radiation over a broad range of frequencies. For more than a century, lightning has been studied using radio-frequency detection systems. And in the past few years, a radio telescope called the Low Frequency Array (LOFAR) has been trained on lightning. This telescope comprises thousands of antennas spread over multiple countries in Europe, and can observe the structure of lightning with unprecedented spatial resolution. Writing in Nature, Hare et al.1 present an analysis of LOFAR observations, and report the discovery of needles — structural features 10–100 metres in length — that extend perpendicularly from initially positively charged lightning channels (see also ref. 2). This finding could lead to a better understanding of lightning and explain why lightning flickers.


Read the paper: Needle-like structures discovered on positively charged lightning branches

A lightning flash is a giant electrical discharge. An analogue in the laboratory is the discharge of an electronic device called a capacitor through a resistor — a process that can be extremely efficient, because the charge on the capacitor decays exponentially with time. The discharge of a thunderstorm by lightning is markedly less efficient, in part because the charge resides on particles that are spatially distributed. An efficient discharge would require the establishment of a conductive path to every charged particle in the storm. Given that air must be ionized to provide all of these paths, such a process would require an unfeasible amount of energy.

Instead, lightning forms a bidirectional channel of ionized air that propagates away from the initiation point with positively and negatively charged ends — known respectively as positive and negative leaders (Fig. 1a). The positive leader extends downwards into a region of negatively charged graupel (soft hail) particles, whereas the negative leader extends upwards into an area of positively charged ice crystals. The discharge of a thunderstorm is therefore much more intricate than that of a capacitor.

Figure 1 | Progression of a lightning flash. a, In a simple intracloud lightning flash, lightning forms a channel of ionized air that propagates away from the initiation point with negatively and positively charged ends, respectively called negative and positive leaders. The negative leader extends upwards into a region of positively charged ice crystals, whereas the positive leader extends downwards into an area of negatively charged graupel (soft hail) particles. b, During the flash, charge is pushed away from the leaders, forming conical structures called corona sheaths. In addition, current cut-off — a large reduction in current flow — occurs in the positive leader. c, Hare et al.1 report that positive charge accumulates at the end of the positive leader and that negative charge piles up near the end of the leader. Small negative leaders (10–100 metres in length), known as needles, are launched perpendicularly from the negatively charged section of the positive leader.

A lightning discharge differs from an idealized capacitor discharge in one other key aspect that is highly relevant to needles: the electrical resistance of lightning channels is not constant, and increases strongly with decreasing current. For example, the resistance per unit length of a channel carrying a current of 1 ampere is about 300 times that of a channel carrying 100 A3. Hare and colleagues emphasize the role of this ‘negative differential resistance’ in provoking current cut-off — a dramatic reduction in current flow — in the positive leader.

The term ‘polarity asymmetry’ refers to differences in the macroscopic behaviour of objects that have opposite attributes, such as positive and negative charge. Polarity asymmetry in lightning leaders is conspicuous, and is ultimately attributable to the marked polarity asymmetry in the charge carriers in ionized air4: free electrons are highly mobile, whereas heavier positive ions are not. Lightning channels are fed by free electrons, with electron convergence at the head of the positive leader and divergence from the negative leader. As a result, the negative leader is fast and energetic, emits copious radio-frequency radiation and produces many free electrons. By contrast, the positive leader is slow and smoothly progressing, emits little radio-frequency radiation and generates few free electrons. The latter characteristics could make the positive leader more fragile, more prone to current cut-off and more likely to exhibit needles than the negative leader.

The needles identified by Hare et al. can now be depicted in the context of polarity-asymmetrical leaders that span positively and negatively charged regions of a thundercloud in a simple intracloud lightning flash (Fig. 1a). During the flash, charge deposited along a leader produces a large radial electric field that pushes charge away from the leader. This discharge forms a conical structure called a corona sheath that expands outwards until the radial electric field becomes smaller than a particular threshold. Smaller sheath radii are therefore associated with larger thresholds. Polarity asymmetry in these thresholds allows the volume of the sheath around the positive leader to be about 10 times greater than that around the negative leader5 (Fig. 1b).

Negative charge carried by graupel particles is mobilized by the volume-filling discharge 6 in the corona sheath of the positive leader. This charge moves towards the positively charged region of the thundercloud, but piles up near the tip of the positive leader (Fig. 1c). Compared with the rest of the leader, this region is least prone to current cut-off because its free-electron population is the most recently formed. Therefore, whereas the lightning on large scales depletes the overall electrostatic energy, the local concentration of negative charge (and electrostatic energy) is enhanced. Small negative leaders — needles — are then launched perpendicularly from the positive leader, and the LOFAR measurements can resolve the speed of their radial progression to verify their negative charge.

Hare et al. emphasize that the diminished flow of negative charge towards the positive end of the thundercloud represents a diminished current in the lightning channel. Diminished current is a prerequisite for runaway instability leading to current cut-off4,7,8 that is not readily accounted for in conceptual models of lightning structure9. In future work, it will be valuable to establish the connection between the formation of needles and the development of recoils and discharges called K changes in the positive leader. Such effects are recognized signatures of current cut-off and the formation of further strokes in the lightning flash. It will also be important to establish the role of the lightning corona sheath in the occurrence of other bidirectional leader developments observed in proximity to positive leaders10,11.

Nature 568, 319-320 (2019)
doi: 10.1038/d41586-019-01178-7



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TREMORS (NO WORMS DETECTED)

NEWS NATURE
18 APRIL 2019

Algorithms spot millions of California’s tiniest quakes in historical data
Project identifies reams of imperceptible tremors that can help to image fault lines in unprecedented detail.




Large earthquakes such as the magnitude-7.2 quake that hit Baja California in Mexico in 2010 are often surrounded by thousands of smaller tremors. Credit: Daniel Conejo/AFP/Getty

When it comes to earthquakes, large, destructive ones dominate the headlines. But seismologists have long known that small quakes, which are created by the near-constant slipping of fault lines and often go unnoticed even by scientists, can illuminate crucial details about all kinds of earthquakes, even really powerful ones.

Now, a team of researchers has used machine-learning and supercomputers to spot millions of these imperceptible quakes — as small as magnitude 0.3 — hiding in the seismological records of southern California, one of the most tectonically treacherous corners of the United States.

The data will allow researchers to improve their understanding of the physical processes that trigger hazardous earthquakes — ultimately boosting hazard-mitigation efforts.

This type of data mining is like gold-mining, says Ken Hudnut, a geophysicist at the US Geological Survey in Pasadena, California, who was not involved with the research. The project can extract ‘gold’ at record efficiencies, and might find riches that no one expected to dig up, he says. The results were published in Science1 on 18 April.

The team’s approach could also be applied elsewhere and to other geological features, such as volcanoes, say the researchers.
Exhuming quakes

The project, called Mining Seismic Wavefields (MSW), began in 2016, and involves researchers at Stanford University in California, the University of Southern California (USC) in Los Angeles, the California Institute of Technology in Pasadena and the Georgia Institute of Technology in Atlanta.

The researchers came up with the idea some time ago, but two key ingredients were missing: vast and detailed seismic data sets created with modern instrumentation, and powerful computer systems to process the data efficiently. The elements finally came together a few years ago, and teams began developing techniques to find small earthquakes in new records.

The Caltech MSW group analysed seismic data known as waveforms, which represent earthquakes, and used their distinctive features to create templates that could ‘show’ algorithms what to look for in a large data set. They fed the templates into supercomputers and used them to detect the elusive fingerprints of tiny quakes in an ocean of noise.
Signal vs noise

But distinguishing between sources of low-level ground shaking is “anything but trivial”, says Yehuda Ben-Zion, acting director of the Southern California Earthquake Center at USC and co-leader of the MSW project. His group, which was studying the anatomy of seismic faults, found that the California ground shakes constantly. Vibrations from planes, trees, houses and even antennas shaking in the wind generate rumbles that, to a seismograph, look like earthquakes and can make up up 10–50% of signals in a set of seismological data.

To separate them out, the team developed machine-learning models and fed them millions of examples of both real quake signals and non-tectonic shaking. The software could “learn to correctly identify never-seen-before waveforms”, says team member Christopher Johnson, a geoscientist at the Scripps Institute of Oceanography in La Jolla, California.

The team also found that seismic records are not always good enough to create sufficient templates for the software to learn what an earthquake in a particular region looks like. So the researchers developed another algorithm, called Fingerprinting and Similarity Thresholding (FAST), which is based on a method developed for audio recognition. But unlike apps such as Shazam that recognize for music on the basis of small clips, FAST doesn’t know what clips from the earthquake ‘song’ sound like. Instead, it looks for snippets in the entire data set that are similar to each other, and flags them as candidate quakes, says Karianne Bergen, a data scientist at Harvard University in Boston, Massachusetts, who co-developed the algorithm while doing her PhD at Stanford.

For the latest paper1, the MSW team applied these approaches to the entire continuous set of data recorded by the prolific Southern California Seismic Network, which has sensors all across the region.

The researchers found 1.81 million previously undetected quakes that took place in 2008–17 — a tenfold increase on the original number catalogued.

Ben-Zion suspects that with improvements in computing power and detection methods, MSW will be able to pick out many millions more quakes even tinier than those they are currently finding.

“We can expand the number of sensors, we can put them in boreholes deep underground to reduce the background noise levels, and we can improve our automated algorithms for finding these weak events in the data,” says lead author Zachary Ross, a geophysicist at Caltech.
Trembling volcanoes

The technique is “be limited by the quality and paucity of data when compared with the high-quality data we have now,” says Lucile Bruhat, an earthquake physicist at the École Normale Supérieure in Paris who is not involved with the project. But “we can, and should, revisit catalogues and past large earthquakes to better characterize what happened at the time”, she says.

Bruhat suggests the technique could also be used to observe mysterious types of earthquake such as ‘slow slip’ events, which take months or years to unfold and are hinted at by numerous miniature rumbles.

Jackie Caplan-Auerbach, a seismologist and volcanologist at Western Washington University in Bellingham, thinks the approach could be applied to volcanoes.

“We know that volcanoes are creaky, unstable things, and the vast majority of their seismic activity is very small”, which makes it difficult to detect, she says. If this work can help extract these rumblings, then researchers will gain insights into the magma and superheated fluids moving about inside them.
doi: 10.1038/d41586-019-01258-8

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Ross, Z. E., Trugman, D. T., Hauksson, E. & Shearer, P. M. Science https://doi.org/10.1126/science.aaw6888 (2019).

CRISPR CRITTERS
NATURE NEWS
23 APRIL 2019

CRISPR gene-editing creates wave of exotic model organisms

But the practical challenges of breeding and maintaining unconventional lab animals persist.

Sara Reardon

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The Hawaiian bobtail squid (Euprymna scolopes) alters the camouflage patterns on its skin based on what it sees.Credit: Eric Roettinger/Kahi Kai Images

Joseph Parker has wanted to know what makes rove beetles tick since he was seven years old. The entomologist has spent decades collecting and observing the insects, some of which live among ants and feed on their larvae. But without tools for studying the genetic and brain mechanisms behind the beetles’ behaviour, Parker focused his PhD research on Drosophila fruit flies — an established model organism.

Now, more than a decade later, the rise of the CRISPR gene-editing technique has put Parker’s childhood dream within reach. He is using CRISPR to study symbiosis in rove beetles (Staphylinidae) in his lab at the California Institute of Technology in Pasadena. By knocking out genes in beetles that live with ants and in those that do not, Parker hopes to identify how the insects’ DNA changed as their lifestyles diverged. “We’re designing a model system from scratch,” he says.

Biologists have embraced CRISPR’s ability to quickly and cheaply modify the genomes of popular model organisms, such as mice, fruit flies and monkeys. Now they are trying the tool on more-exotic species, many of which have never been reared in a lab or had their genomes analysed. “We finally are ready to start expanding what we call a model organism,” says Tessa Montague, a molecular biologist at Columbia University in New York City.

Montague works on the Hawaiian bobtail squid (Euprymna scolopes) and the dwarf cuttlefish (Sepia bandensis), species whose unusual camouflage acts as an outward display of their brain activity. The cephalopods project patterns onto their skin to match what they see around them. But probing how their brains process stimuli has been difficult. Researchers would normally do this by embedding electrodes or other sensors into the skull — but squid and cuttlefish are boneless.

Last year, Montague and her colleagues successfully injected CRISPR components into cuttlefish and bobtail-squid embryos for the first time. Now, they are trying to genetically modify the cephalopods’ neurons to light up when they fire.
Technical knock out

Other researchers are using CRISPR to study species’ distinctive social behaviours. Daniel Kronauer, a biologist at the Rockefeller University in New York City, has created raider ants (Ooceraea biroi) that cannot smell pheromones. In experiments, the genetically modified ants were not able to sustain the complex hierarchy seen in a normal raider-ant colony1. The scientists are now using CRISPR to alter genes thought to influence raider ants′ behaviour.

Then there are species that threaten human or environmental health — such as the pea aphid (Acyrthosphion pisum), an insect that attacks legume crops worldwide. To edit the aphid’s genome with CRISPR, a team led by Shuji Shigenobu, an evolutionary geneticist at the National Institute for Basic Biology in Okazaki, Japan, had to manipulate the insect’s complex life cycle. Female aphids born in summer reproduce asexually, by cloning themselves, whereas those born in autumn lay eggs.

Shigenobu’s team set up an incubator that simulated the cool temperatures and short days of autumn so their aphids would lay eggs that the scientists could inject with CRISPR components.

After four years, the team succeeded in editing a pigment gene as a proof of concept, Shigenobu announced last month during a conference at the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Virginia. He hopes that by modifying other parts of the aphid’s genome, researchers can learn more about how the insects interact with plants. That information could lead to the production of better pesticides.
Inching forward

Developing animal models requires immense amounts of time and money, and until recently there was little support for such work. In 2016, the US National Science Foundation launched a US$24-million programme to create model organisms — and in doing so, reveal the genetic and molecular mechanisms behind complex traits and behaviours.

The programme supports research to create tools for probing species’ genomes, study organisms’ life cycles and develop protocols to raise these species in the lab. This support has begun to pay off: in March, for instance, researchers at the University of Georgia in Athens said2 that they had used CRISPR to create the first genetically modified reptile, the brown anole (Anolis sagrei).

Despite such promising early results, the push to create model organisms with CRISPR has revealed how little is known about many species’ genomes, life cycles and habits. Researchers face practical challenges such as determining how to inject CRISPR components into embryos and coaxing finicky, fragile species to breed in the lab.

“The reason classic model systems were chosen was they’re basically pests. Nothing can stop them growing,” Montague says. “But if we take on this challenge of working on new organisms because they have an amazing feature, they’re often not happy to grow under [just] any conditions.”

This has forced scientists to weigh the effort required to study a particular trait against the potential rewards. Modifying a genome requires a deep understanding of a species’ behaviour and lifecycle — a tall order when that organism is studied by only a handful of people worldwide. “People are not choosing these model systems lightly,” says David Stern, a biologist at Janelia.

Stern knows this first hand: he and his colleagues succeeded in breeding one fruit-fly species only after discovering that the insects need an olfactory cue to lay eggs — the smell of a particular chemical made by plants.

Still, researchers’ interest in developing atypical animal models continues to grow. Montague and her colleagues have created a tool called CHOPCHOP, which allows them to design a CRISPR system for editing specific genes in any DNA snippet. So far, scientists have sent her genetic sequences from more than 200 different species, including plants, fungi, viruses and farm animals.

“I had this weekly reminder that these molecular tools do work in pretty much every organism on the planet,” Montague says. “It’s such an exciting time to work on any model organism — especially these new and weird creatures.”

Nature 568, 441-442 (2019)
doi: 10.1038/d41586-019-01300-9



References

1.

Trible, W. et al. Cell 170, 727–735.e10 (2017).
2.

Rasys, A. M. et al. Preprint at bioRxiv https://www.biorxiv.org/content/10.1101/591446v1 (2019).

Climate Crisis: 

South African And Global Democratic Eco-Socialist Alternatives

Vishwas Satgar
NYU Press, Feb. 28, 2018 - Political Science - 372 pages
Capitalisms addiction to fossil fuels is heating our planet at a pace and scale never before experienced. Extreme weather patterns, rising sea levels and accelerating feedback loops are a commonplace feature of our lives. The number of environmental refugees is increasing and several island states and low-lying countries are becoming vulnerable. Corporate-induced climate change has set us on an ecocidal path of species extinction. Governments and their international platforms such as the Paris Climate Agreement deliver too little, too late. Most states, including South Africa, continue on their carbon-intensive energy paths, with devastating results. Political leaders across the world are failing to provide systemic solutions to the climate crisis. This is the context in which we must ask ourselves: how can people and class agency change this destructive course of history? Volume three in the Democratic Marxism series, The Climate Crisis investigates eco-socialist alternatives that are emerging. It presents the thinking of leading climate justice activists, campaigners and social movements advancing systemic alternatives and developing bottom-up, just transitions to sustain life. Through a combination of theoretical and empirical work, the authors collectively examine the challenges and opportunities inherent in the current moment. This volume builds on the class-struggle focus of Volume 2 by placing ecological issues at the centre of democratic Marxism. Most importantly, it explores ways to renew historical socialism with democratic, eco-socialist alternatives to meet current challenges in South Africa and the world.

Neoliberalism and Climate Policy in the United States:
From market fetishism to the developmental state



This book explores how Washington’s efforts to act on climate change have been translated under conditions of American neoliberalism, where the state struggles to find a stable and legitimate role in the economy, and where environmental and industrial policy are enormously contentious topics.

This original work conceptualizes US climate policy first and foremost as a question of innovation policy, with capital accumulation and market domination as its main drivers. It argues that US climate policy must be understood in the context of Washington’s broader efforts over the past four decades to dominate and monopolize novel high-tech markets, and its use of immense amounts of state power to achieve this end. From this perspective, many elements of US climate politics that seem confusing or contradictory actually appear to have an obvious and consistent logic.

This book will be of particular interest to students and scholars of IPE, as well as individuals generally interested in gaining a stronger understanding of US climate politics and policy, and the role and influence of neoliberalism on contemporary economic governance.

Underwater ritual offerings in the Island of the Sun and the formation of the Tiwanaku state

Christophe Delaere, José M. Capriles, and Charles Stanish

PNAS April 23, 2019 116 (17) 8233-8238; 
first published April 1, 2019 https://doi.org/10.1073/pnas.1820749116

1. Contributed by Charles Stanish, February 27, 2019 (sent for review December 6, 2018; reviewed by John Janusek and Joyce Marcus)

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Significance

Ritual and religion are significant factors in primary or archaic state formation. These beliefs and practices not only legitimize these new political organizations in their ability to control supernatural forces, but also incentivize intragroup cooperation by punishing freeloading and rewarding cooperative behavior. Recent archaeological excavations from an underwater ceremonial location near the Island of the Sun in Lake Titicaca have revealed the remarkable constituent elements of repetitive rituals practiced by the Tiwanaku state between the 8th and 10th centuries CE. Evidence of animal sacrifice and high-value offerings of vessels, gold, shells, and lapidary stones on a strategically located reef illustrates how power was consolidated in one of the earliest Andean states.

Abstract

Considerable debate surrounds the economic, political, and ideological systems that constitute primary state formation. Theoretical and empirical research emphasize the role of religion as a significant institution for promoting the consolidation and reproduction of archaic states. The Tiwanaku state developed in the Lake Titicaca Basin between the 5th and 12th centuries CE and extended its influence over much of the south-central Andes of South America. We report on recent discoveries from the first systematic underwater archaeological excavations in the Khoa Reef near the Island of the Sun, Bolivia. The depositional context and compositional properties of offerings consisting of ceramic feline incense burners, killed juvenile llamas, and sumptuary metal, shell, and lapidary ornaments allow us to reconstruct the structure and significance of cyclically repeated state rituals. Using new theoretical tools, we explain the role of these rituals in promoting the consolidation of the Tiwanaku polity.

CHAPTER 18

ABIEZER COPPE AND THE RANTERS 

ARIEL HESSAYON 

In 1652 Mary Adams of Tillingham, Essex apparently died by her own hand. According to a pamphlet entitled The Ranters Monster printed at London for George Horton (Figure 18.1), Adams claimed that she had been made pregnant by the Holy Ghost. Furthermore, she reportedly denied the Gospels’ teachings, wickedly declaring that Christ had not yet appeared in the flesh but that she was to give birth to the true Messiah. For these supposed blasphemies Adams was imprisoned. After a protracted labour of eight days, she gave birth on the ninth day to a stillborn, ugly, misshapen monster. This loathsome creature was said to have neither hands nor feet, but claws like a toad. Adams herself became consumed by disease, rotting away; her body disfigured by blotches, boils, and putrid scabs. To compound her sins she refused to repent and then committed the terrible crime of suicide by ripping open her bowels with a knife. The account in The Ranters Monster was reproduced in some contemporary newsbooks and subsequently in a broadside enumerating the great blasphemers of the times. It was, however, fictitious. While the pamphlet formed part of the genre of monstrous births, which tended to be interpreted as providential signs warning against private and public sin, it also served another function: as an admonition against the licentiousness of the Ranters and an affirmation of the dreadful divine punishments that awaited all such reprobates.

Gender,Production, and ‘the Transition to Capitalism’: Assessing the Historical Basis for a Unitary Materialist Theory

Gary Blank

York University

ABSTRACT: 

When socialist feminists discussed the potential and pitfalls of Marxism in the “domestic labour debate,” the specific relationship between patriarchy and capital emerged as a defining concern. While offering a trenchant critique of orthodox Marxism, the tenor of the debate was highly abstract and theoretical, and largely ignored the question of capitalism’s origins. Political Marxists, in contrast, have devoted fastidious attention to this question in their own attempt to renew historical materialism; but their dialogue has dedicated little attention to questions of gender, families, and social reproduction in the feminist sense. This paper makes an initial attempt at closing the analytical gap between these two historical materialist traditions. It departs from an unresolved theoretical impasse within the socialist feminist tradition: how to conceive of the imperatives of capital accumulation and class in a way that avoids both reductionism and dual-

ism. I argue that this tension stems principally from an inadequate historicization of capitalism. A critical assessment of Wally Seccombe historical work illustrates how political Marxism can be deployed to correct this deficiency, while also revealing the extent to which these concepts must be rethought in light of materialist feminist concerns. A synthesis of

the two traditions offers a more complete and effective account of the transition, while providing a basis for a unitary materialist theory.

KEYWORDS: Brenner debate, materialist feminism, political Marxism, primitive accumulation, social reproduction, socialist feminism, transition from feudalism to capitalism