## Despite a mistaken mathematical proof, you do only need four colors to make a good map

Alfred Kempe's 1879 proof of the Four Color Theorem contained a mistake. Nearly a century, later his work was vindicated

Mathematics

Freelance

Mathematicians are human, just like the rest of us, which means that they sometimes make mistakes. As their work is read by other mathematicians, both during peer review and after publication, we might expect errors to be quickly spotted and addressed. But a fatal mistake in Alfred Kempe's 1879 "proof" of the Four Color Theorem remained unnoticed for over a decade.  The error was finally uncovered by Percy Heawood in 1890.

The Four Color Theorem states that for any map of contiguous countries drawn on a plane only four colors are needed to ensure that adjacent countries are given different colors. In the heart of his “proof,” Kempe had to consider a number of different cases of possible map configurations.  To tackle these cases, he invented a new mathematical tool called Kempe chains. However Heawood discovered that Kempe's treatment of one of these cases didn’t work and presented an example to show how his reasoning failed.

Heawood's discovery did not mean that all was lost, though. First, Heawood showed that Kempe's work was enough to establish a weaker result called the Five Color Theorem which says that only five colors are needed to color a map in the required way.  Second, although Kempe's proof was flawed, the Four Color Theorem was true. It was first proved successfully, though somewhat controversially, using a computer by Kenneth Appel and Wolfgang Haken nearly a century later in 1976. And Kempe’s ideas played a significant role in their work. So while Kempe made a mistake in his “proof,” it still contained valuable mathematics.

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## This backpack-mounted exoskeleton turns excess walking force into electricity

This assistive technology could make rehabilitation after accidents and even day-to-day activities easier

Microbiology

University of Michigan

Walking takes little brain power, but it does require energy. In fact, it is the most energy-intensive activity that we do as part of our daily lives. What if we could put on an exoskeleton that worked with our muscles to ease some of the metabolic burdens of walking? Such a suit could assist in accident rehabilitation, help outdoor adventurers or on-foot search parties hike longer with ease, and even make day-to-day activities like running errands less taxing.

In a study recently published in the journal Science, a team of engineers from Queen's University in Canada developed a backpack-mounted exoskeleton that reduces the metabolic cost of walking by 2.5 percent. At the same time, the device harnesses energy produced by walking and converts it to 0.25 watts of electricity (for reference, cell phone chargers generally use about 2-6 watts of electrical power).

Weighing approximately two pounds, the exoskeleton consists of cables that run parallel to a user’s hamstrings and attach to their ankles. The cables feed into pulleys on the user’s back, which connect to a generator. The system works by helping slow the leg down during the late "swing phase" of the walking cycle, after the leg has extended forward and the foot is about to touch the ground. Essentially, the device helps the hamstrings "put on the brakes". The generator powered through this resistance converts the energy into electricity. This electrical power could then be used to supply people with electricity or powered, assisted movement.

This study, among others, illustrates that exoskeletons are not a futuristic fantasy, but a real possibility. It points to practical implications for exoskeletons beyond assisting mobility,. As exoskeletons become more wearable, intuitive, and optimized, they have a greater chance of entering the mainstream market. Some day, we may all have an exoskeleton in our closets.

## Bacteria mix their genomes with partners so much they turn themselves into hybrids

Bacteria share genes — including those for antibiotic resistance — like trading cards

Geomicrobiology

Massachusetts Institute of Technology

This is part of Stoned Science — science that makes you go "whoa." Or is it woah?

If lighting up makes you want to snuggle up, then it's good thing you're not bacteria — otherwise those innocent post-brownie cuddle puddles might end up leaving you with some extra DNA you didn't ask for. When they get close enough, certain bacteria share packets of DNA with each other in what essentially looks like a super intimate handshake or hug.

This process is called bacterial conjugation, and it's about as close as bacteria get to sex. But unlike sex, conjugation isn't a reproductive process. Instead of leading to new bacteria, it transfers genes from one existing bacterium to another.

One partner, called the donor, builds a little appendage called a pilus out of protein and uses it to connect with the recipient cell, reeling it in for a close embrace. The two temporarily fuse a small section of their cell membranes, allowing the donor to transfer a bit of DNA to the recipient. Usually, the two bacteria simply exchange DNA and then go on their merry ways. But certain bacteria can end up scrambling their genomes so thoroughly that they emerge from their liaison as hybrid mixtures of each other.

But conjugation isn't all innocent hugs and good vibes. It has a dark side. Gene transfer via conjugation is so important for spreading antibiotic resistance that some scientists have even proposed developing drugs that target conjugation systems as a way to gain the upper hand in the antibiotics arms race.

## Domestic cats fall for the same visual illusions as we do

Our feline friends are just as likely to sit inside of a fake square as a real one

Ecology & Evolutionary Biology

University of Florida

Anyone with a cat (or internet access) has likely observed their tendency to seek out and sit in boxes, bags, baskets, and even a simple square drawn on the ground, as demonstrated by Twitter’s #CatSquare trend.

A team of psychologists decided to use this feline behavior to investigate whether cats are susceptible to a well-known visual illusion: the Kanizsa square. A Kanizsa square is made of four small solid-colored circles, each with a right angle cut out so that only ¾ of the circle remains. These circles are arranged in a large square shape and rotated so that the missing parts face inwards, creating the illusion of an actual square sitting above them.

A 1988 study provided some evidence that cats perceive the Kanizsa square the same way that humans do, but that study only included two cats trained in a lab. Scientists behind a recent study, published in Applied Animal Behaviour Science, wanted to test a wider range of cats and capture their natural behavior at home. To do this, they turned to social media to recruit participants.

They asked cat owners to cut out three different stimuli: a real square, a Kanizsa square, and a rotated Kanizsa in which the circles were turned outwards, causing the illusion to fail. Each day, the cat owners placed two of these stimuli on the floor and then watched their cat for five minutes.

Thirty cats were tested over six days, and among them, they sat within the real square eight times, the Kanizsa square seven times, and in the rotated Kanizsa only once. In the trials where the cats had a choice between the real square and the Kanizsa square, they showed no preference between them. This indicates that cats may perceive illusory squares to be as valid, and as comforting, as real squares.

So, in addition to showing that cats really do like sitting in two-dimensional squares, the researchers also demonstrated that cats perceive some of the same visual illusions that humans do. Despite the many differences in the eyes and brains of humans and cats, we may see and interpret our environment in strikingly similar ways.

## Ancient poop analysis reveals extinct species of bacteria

Scientists analyzed bacterial genomes from 1000-2000 year feces

Neuroscience

Half the cells in our body aren't human. Don't worry, these non-human cells aren't harmful. In fact, they're crucial to your health and make you, you. Trillions of bacteria, viruses and fungi flourish within us. We co-evolved with the microbial community living in our guts. Microbial signaling plays a crucial role in maintaining our health

As our society became industrialized, we lost many microbes that once lived within us. Could any of these missing microbes help us develop new treatments?

Often, scientists look at modern hunter gatherer societies to study microbiome industrialization. Instead of relying on these humans as a proxy, scientists extracted DNA from ancient poop. It dated back between 1000 and 2000 years old, found in rock shelters in Utah and Mexico. They published their glimpse into the ancient gut microbiome in Nature in May.

In analyzing eight ancient poop samples, the researchers travelled back in time. They found overlap between modern hunter gatherer societies and the ancient poop.  Roughly two of every five bacterial genomes extracted from the ancient poop were new. These never-before seen microbial species likely went extinct as we became more industrialized.

Diet is only one of many factors that changed our microbiomes. As we sequence more ancient poop, we will zero-in on the factors shaping the modern microbiome.

Scientists found so many new species in only eight samples. Of course, these samples are precious and limited. It is rare that we find these well-preserved specimens. But as out sequencing technology improves, we might be able to extract more information from ancient poop.

## This ancient child burial is the world's oldest, dating back 80,000 years

The burial site adds to the history of humankind's symbolic commemoration of the dead

Evolutionary Anthropology

Duke University

Homo sapiens emerged around 300,000 years ago in Africa, and traces of modern use of symbols in our species date back around 160,000 years . Today, humans are considered unique in the natural world for the universality with which we symbolically commemorate the deceased. Despite this, the oldest known burial in Africa was only 74,000 years old until now.

In a new study, a team of researchers described the oldest burial in Africa to date, containing the nearly 80,000 year old skeleton of a 2.5 to 3 year old child in a cave off the coast of South Africa. Several features of the burial, including the change in soil color and texture, indicate that the pit was created intentionally, rather than an existing natural feature.

According to their analysis, the child was placed in the pit shortly after death, before the tissues could deteriorate, which would displace the bones. However, some bones in the upper body were rotated, suggesting that the child had been partially wrapped in and supported by a perishable material. Interestingly, though the researchers identified the child as belonging to Homo sapiens, they note that some dental features differ from those seen in humans today — those differences resemble dental patterns found in Neanderthals.

Older human and Neanderthal burials dating to the same archaeological period have been previously found in the Levant. This new find highlights the biological and cultural diversity of different hominin populations during this period, and showcases the care with which individuals were buried tens of thousands of years ago.

## Bioengineered bacteria can make dyes more sustainable

Researchers gave bacteria the genetic tool they needed to make indigo naturally

Chemical Biology, Chemical Engineering, Neuroscience, Psychology, and Chemistry

University of Waterloo

Textile dyes are one of the leading causes of water pollution. The dyeing process uses lots of water, and much of this water ends up in nearby rivers and streams. And dye wastewater, such as the effluent from denim production, contains dangerous chemicals. Toxic chemicals are also sometimes left behind in your clothes after the dyeing process.

Bioengineering bacteria and fungi is one way to reduce the environmental impact of dye production, since it can reduce the amounts of dangerous chemicals needed in the process. In a recent study published in ACS Sustainable Chemistry & Engineering, biomolecular chemists injected DNA into a type of bacterium, Corynebacterium glutamicum, that already produces the building blocks of the blue dye, indigoidine. The specific segment of DNA, a "blue-pigment indigoidine synthetase" gene, allowed the bacteria to put those building blocks together. The bacteria produced large amounts of the dye, which the scientists then used to color white cotton.

If scientists can engineer bacteria that produce dye at a level comparable to industry, we could see a shift towards the use of these greener methods in the textile industry. This will lead to greater sustainability in an unsustainable industry.

## Scientists celebrate Inverte-Butt-Fest, a photographic homage to spineless backsides

"Invert butts should be celebrated because they have a wide diversity in form and function, and because they bring us all joy"

Science and Health Journalism and Chemical Engineering

Yesterday scientists and photographers took to Twitter to celebrate International Invertebrate Butt Day, or #invertebuttfest. Some of them are fuzzy. Some are wet and slimy. Many are literal hard-asses, strengthened by one of nature's toughest materials called chitin. The niche trend is also taking place in honor of biologist Maureen Berg's birthday. (Berg has previously given talks about invertebrate butts, and has previously called for June 9th to be Invert Butt day.)

"The whole idea is that, we love butts, especially invert butts, and decided that there should be a dedicated day to celebrating them," Berg says. "Invert butts should be celebrated because they have a wide diversity in form and function, and because they bring us all joy."

We at Massive have a soft spot for butts. We, in fact, dedicated a whole month to them. That's because butts are fascinating. Humans have evolved anatomically interesting ones, and we use their deposits to track disease. Other animals evolved to literally be a butt's output, to escape predators. And butts can be important tools for animal scent-based communication

Invertebrate butts are of course, nothing like ours. Spiders aren't fleshy and bees don't have anuses. But there's no reason to identify part of their anatomy as a butt in any case. The precise definition of a butt is a bit arbitrary. In an interview last year, ecologist and butt science author Dani Rabaiotti told Massive: "I usually just refer to any end of an animal that’s opposite its head as a butt." So there you have it, scientific validation for the ubiquity of butts. Here are some of our favorites invertebutts:

## Seeing in different lights paints a more detailed picture of Jupiter

Newly released images show the planet in infrared, visible, and ultraviolet light

Astronomy

Vera C. Rubin Observatory

Astronomers have just released three newly processed images of Jupiter at three different wavelengths, a combination of photos from the Hubble Space Telescope and the Gemini North telescope in Hawai’i that were taken in January 2017. By observing the planet at infrared, visible, and ultraviolet wavelengths of light and comparing the images to radio signal detections by the Juno spacecraft, scientists can better understand Jupiter's atmospheric phenomena such as wind patterns and cyclones. The radio signals detected by Juno correspond to blasts of lightning in Jupiter’s atmosphere. The location of these signals can be mapped to the images to see which types of clouds are present and how they move over time. More information about the science behind these images was published last year in The Astrophysical Journal.

Image diversity is important because each wavelength “sees” through different layers of the atmosphere. For example, the Great Red Spot is clearly visible in both the ultraviolet and visible images, but appears as a bright crescent in the infrared image. This glowing semicircle represents a gap in the clouds, a feature distinguishable with longer wavelength infrared light that can penetrate the upper atmospheric layers of thin haze. However, the gap is hard to detect with visible light since that haze is almost the same color as the thicker storm clouds surrounding it. In the ultraviolet image, the Great Red Spot appears larger and more uniform since the shorter wavelength ultraviolet light mostly captures the haze, obscuring features of the spot in lower layers that can be seen with visible light. In this way, each image is a separate piece of the puzzle, together giving more insight into what’s actually happening on the planet.

Ultimately, the trifecta of the Hubble, Gemini, and Juno will enable scientists to track changes in Jupiter’s atmosphere and perhaps even provide insight into one of the planet’s biggest mysteries: Why is the Great Red Spot shrinking?

## Ocean mammals keep cancer at bay with tumor suppressing genes

Studying how whales and dolphins can evade cancer could help us suppress it in humans

Immunology and Cell Biology

University of Cambridge

Cancer is a disease in which abnormal cells divide uncontrollably. Most cancers start due to gene mutations which accumulate over the course of an animal’s life. Each time a cell divides, there is chance that the genes within the cell will mutate. If genes which control the normal growth, division, and death of cells become mutated, the cell can become cancerous. Theoretically, the longer an animal lives and the more cells within its body, the higher the chances are that enough mutations will accumulate for cancer to develop — but not always.

Whales, dolphins, and porpoises belong to a group collectively known as cetaceans, containing some of the largest and longest-lived species of mammals on Earth. Yet, cetaceans have some of the lowest cancer rates. This lack of cancer suggests cetaceans must have evolved effective cancer suppression mechanisms which humans and other mammals lack.

Researchers trying to better understand how cetaceans suppress cancer studied the evolution of over 1000 tumor suppressor genes, or TSGs in 15 mammalian species, including cetaceans. TSGs are known to affect cell division, repair mistakes in DNA, and control when cells die — important processes for keeping cancer at bay. Published in Proceedings of the Royal Society B, their results show that over time cetacean species including orcas and bowhead whales had positively selected TSGs that are linked to a variety of cancers. The team also found that cetacean species gained and lost genes at a rate more than double that of other mammalian species, which may have accelerated evolution of TSGs in cetaceans.

These findings point to the evolutionary mechanisms that allowed large, long-lived species to overcome the threat of cancer. By studying the genes implicated in cancer suppression and understanding how they might do so, researchers may gain useful insights into how to suppress cancer in humans.

## China lands its first rover on Mars, becoming the second country to do so

The Zhurong rover is the first Mars rover to carry a magnetometer

Astronomy and Astrophysics

University of California, Los Angeles

On May 14, China successfully landed a rover on Mars with its Tianwen-1 mission, becoming the second country to land a rover on our neighboring planet. The Zhurong rover now joins the handful of American rovers — Sojourner, Spirit, Opportunity, Curiosity, and the current Perseverance mission — already on the Red Planet. This historic event follows right on the tails of another nation’s first success: the United Arab Emirates’s first interplanetary spacecraft, a Mars orbiter known as Hope, which reached the planet's orbit in February.

The Zhurong rover is about 500 pounds (the weight of a male black bear), much smaller than the newer, heftier NASA rovers. Zhurong is powered by solar panels and expected to operate for only about three months, although other rovers have lasted far longer than their planned missions. It’s accompanied by the Tianwen-1 orbiter, which released its lander down onto the Martian surface and now serves as a communications relay. The orbiter will survey the surface and report to the lander where it should investigate further, while the rover will explore the surface geology and map the distribution of water-ice

The Tianwen-1 lander, carrying the Zhurong rover, touched down in Utopia Planitia, a region also visited by the Viking 2 lander. This is a particularly interesting region for the search for life, since previous evidence suggests that water-ice might be lurking under the surface here. The rover is equipped with cameras, ground penetrating radar, a spectrometer, and even a magnetometer — the first on a Martian rover. Measuring the Martian magnetic field might clue scientists in as to why Mars lost its atmosphere billions of years ago, making it the uninhabitable place it is today.

This successful first for China opens the door for future exploration such as a planned sample return by the 2030s, adding yet another crucial tool to humanity’s search for water and life on the Red Planet.

## Extinction risks in a rapidly warming planet depend on previous slow temperature swings

Considering "climate memory" changes the risk calculation as much as an organism's geographic range or abundance

Developmental Biology

University of California, Berkeley

Rising global temperatures are one of the biggest threats to biodiversity. The slow creep up of the thermometer — 1.2 degrees Celsius over the past 150 years — is blisteringly fast on a geological timescale, and species can only adapt so fast. But they’ve evolved to deal with changing temperatures in the past — sometimes, very far in the past. Scientists writing in Nature earlier this year found that considering this “memory” of climate history helps better predict extinction risks as the planet continues to heat up.

The researchers tracked thousands of animal extinctions through the fossil record and compared their frequencies under different prehistoric combinations of long- and short-term temperature changes. If a rapid change in temperature was preceded by a slower temperature change in the opposite direction, the rapid change was usually less deadly. They presume this occurs because the second change returns to distant-past temperatures for which species remained fit, after timescales as long as 60 million years. On the other hand, rapid temperature changes in the same direction as a previous slower change were especially risky.

The effect of prior long-term temperature is strong enough to seriously impact predictions of extinction risk for any given group of species. According to their results, it changes the risk calculation as much as its geographic range or abundance. And, while even the “short-term” prehistoric extinctions happened over timescales far slower than today’s maelstrom of extinction, long-term temperature effects provide a bit of hope: The rapid warming of the Anthropocene was preceded by a long global cooling period, which could make climate change a little less deadly.

## Detecting cancers with neural networks requires a balance of rewards and penalties

Researchers improved AI tumor detection by penalizing it for learning where the scans originated

Computer Science

University of Manchester

Neural networks, a type of machine learning algorithm that work similarly to the way our brains so, are bad at dealing with inputs that are different to what they’ve seen before. Facial recognition algorithms, for example, often fail to recognize the faces of Black people, typically because the algorithms were trained on mostly white faces.

The same can happen with tumor detection. When training a neural network to detect tumors in MRI scans, differences between the scanner setups at each hospital mean that a neural network trained and proficient with data from one hospital performs worse on scans made somewhere else.

One approach to making a more generally useful network is to penalize it for learning information that you’re not interested in. In a study published in the journal NeuroImage, researchers trained their network by rewarding it for identifying tumors correctly and penalizing it for being able to guess which hospital the scan was from. This arrangement pushed the network to learn ways to identify tumors without relying on scanner signatures specific to any one hospital. When they compared their network to a similar one without this technique, their network did much better on scans from new locations than the old network did.

This technique can be used to make neural networks that work better on new data that is different from the data they saw during training. This has the potential to improve the usefulness of neural networks for real life medical diagnosis assistance.

## Why don't hibernating bears get osteoporosis?

Scientists look to bears' genes for answers

Animal Physiology

University of Winnipeg

In humans and some animals, long periods of physical inactivity can lead to osteoporosis, a disease where bones break down and become weak. Osteoporosis is usually caused by either bone not being formed or an increase in bone resorption (where components of bone are reabsorbed into the body). But bears are inactive for 4-6 months of the year during their winter hibernation periods, yet they do not develop osteoperosis. New research, published in Scientific Reports, explores how black bears manage to escape this fate.

During hibernation, black and grizzly bears (Ursus americanus and Ursus arctos horribilis) are known to decrease their metabolic rates by about 20-75 percent to save energy, relying solely on fat stores as their energy source. This new study shows that when bears reduce their metabolism, genes involved in bone resorption become less active. Additionally, there is no increase in the gene expression associated with bone formation or osteoblasts (cells that make bones). The researchers also found evidence of that genes involved with energy production from bone and bone marrow become more active during hibernation, which may provide the bears with an additional energy source during fasting.

## Feeding gut bacteria may reduce anxiety in women

In a trial, women who took fiber supplements reported lowered anxiety compared to a placebo

Neuroscience

In the last decade, we've learned so much about the microbial organisms living in our gut. The bacteria in our guts play important roles across our body, including digestion, stress signaling, and immune function. Despite exciting findings in rats and mice, few of these findings have translated to humans thus far.

Nonetheless, research on the dietary fibers that these microbes feed on is yielding exciting results. These fibers cannot be broken down by our enzymes. Only our gut bacteria can digest them. In the process, the bacteria generate byproducts that interact with our nervous systems. Past research has shown that these byproducts reduced perceived stress in men. Now, a new study finds that galacto-oligosaccharide (GOS) fibers also reduce perceived anxiety in healthy women.

Nicola Johnstone of the University of Surrey and her colleagues designed a double-blind, placebo-controlled trial. Johnstone recruited 48 women (ages 18-25) to provide poop samples and undergo psychological testing. The participants were assessed in the beginning of the experiment. Then, for four weeks, they ingested either a small packet containing GOS or a placebo. After, they participated again in the same psychological tests.

At both time points, the researchers collected samples for microbiome analysis. They also conducted questionnaires to assess the participants' moods before and after the intervention, and measured their and attention through the psychological tests. During these four weeks, all the participants kept a food diary.

The participants who took GOS showed a small increase in the growth of the gut bacterium Bifidobacterium, which feeds on these fibers. When Johnstone and her team analyzed the impact of GOS on anxiety, they found that GOS reduced self-reported anxiety in women with high-baseline anxiety. Women that had a low anxiety score at baseline did not experience a further reduction even in the GOS group. GOS did not associate with any other psychological measures or changes.

## Even short-term exposure to pollution can reduce mental performance

New results from the Normative Aging Study highlight the connection between air pollution and cognitive function

Neuroscience

Medical College of Wisconsin

If you have ever traveled from the center of a big city to a rural area, or the other way around, one of the starkest contrasts is the change in air quality. Although there have been significant decreases in emissions recently, there are still regions where peaks of air pollution are reported. Leaving the climate catastrophe caused by burning fossil fuels aside for a minute, scientists have recently found that these pollutants also have a direct toll on our brains.

Take for instance black carbon, a material emitted from gas and diesel engines and coal-fired power plants, and also one of the components of fine particulate matter (PM2.5). In both children and adults, exposure to this pollutant has been associated with poor cognitive abilities over the years. What Xu Gao and their colleagues discovered and demonstrated in a new paper, however, is that even short exposures can also cause significant declines in cognition.

The researchers were part of the Normative Aging Study, a cohort of older men from the greater Boston area. Alongside daily measurements of the levels of both PM2.5 and black carbon, over the period of 28 days, the team conducted two tests on 954 participants: the global cognitive function and Mini-Mental State Examination. They found that higher short-term exposure to PM2.5 reduced scores on both tests, and that even small concentrations of PM2.5 had a large effect. The effects of pollution were less for participants who used nonsteroidal anti-inflammatory drugs such as ibuprofen than for those who did not.

While we already knew that air pollution has many different adverse effects on our health, this is the first time scientists have shown how these effects can manifest in short-term exposures, to relatively small concentrations of pollutants.

## New battery made from amino acids is light, functional, and recyclable

Chemistry

University of Michigan

Sandwiched inside your laptop, at the back of your smartphone, and under the hood of your dream electric car are powerful and lightweight lithium-ion batteries. Even though these batteries are found inside the technology we use every day, they are rarely recycled — which means that the valuable metals inside them are not recovered for reuse.

Researchers at Texas A&M wanted to build a battery that would be lightweight and powerful, like lithium-ion batteries, but that would be more easily recyclable. To do this, they did something that had never been done before: they built electrodes, which transfer electrical charges in and out of a battery, with degradable polymers instead of metals. Their results appear in the journal Nature.

The researchers chose polymers called polypeptides because these polymers break apart into their building blocks, amino acids, when heated with just the right amount of acid. Polypeptides are not inherently conductive, though, so the researchers chemically modified them by attaching structural units that can transfer electrons back and forth. They then built electrodes by mixing the polypeptides with carbon black, another conductive material, and a binding material to hold everything together.

After successfully charging and draining the new batteries up to 250 times, the researchers disassembled the batteries and broke the polypeptide electrodes down into amino acids and other small molecule building blocks that could be reused to re-build battery electrodes later. Although the polypeptide batteries didn’t perform quite as well as traditional lithium-ion batteries, they are an exciting alternative because the energy storing materials inside them were easily recovered. By degrading on-demand, these batteries could pave the way as a new class of recyclable batteries for the technology that we use every day.

## Scientists turn to a chemical trick to fool flies into eating bitter chow

This will help uncover how flies react to bitter-tasting compounds

Chemical Biology

When was the last time you had something bitter? The more bitter the food is, the less you probably want to eat it. And we are fortunate because of that — throughout the course of evolution, bitter sensations have kept humans away from potentially dangerous food or toxic molecules.

A similar sensory ability has also been detected in other animals such as rodents and Drosophila flies. While rodents have somewhat similar bitter taste receptors to humans, flies possess what are known as bitter-sensitive neurons located in their taste organ. But, similar to most animals, once the receptor is activated by contact with a bitter chemical, an aversive reaction is induced, and the flies stop eating the bitter food. Scientists have even observed that insects will willingly starve just to avoid the noxious compounds, skewing results of studies that involve feeding bitter food to flies.

Recently, researchers at Shoolini University of Biotechnology and Management Sciences in India published a method to trick flies into eating bitter compounds. They encapsulate these appalling molecules inside donut-shaped molecular cages known as cucurbiturils (CB). In the study, researchers prepared tweaked mixtures of caffeine and strychnine, a highly toxic pesticide commonly used for rodents, by confining them inside the molecule “CB7” – cucurbiturils formed by seven repeating units. As predicted, the flies found these masked compounds more palatable and were more willing to feed on CB7-caged caffeine and strychnine molecules.

Being able to feed insects using this method opens up a new area of exploration in elucidating flies’ taste experience on bitter food, as well as the relationship between bitter molecules and toxicity.

## Al evitar a los pumas, los ciervos están cambiando la vegetación a su alrededor de forma drástica

El miedo a los humanos influencia el comportamiento de los animales, y esto, a su vez, afecta las plantas que comen

Ecology and Conservation Biology

University of the Witwatersrand, Johannesburg

This Lab Note is also available in English

Los humanos modificamos nuestros alrededores como mejor nos parece. Somos capaces de eliminar cualquier animal, desde un caracol inconveniente en el jardín hasta un lobo con la costumbre de matar ganado. No es de extrañar que los animales nos tengan miedo.

Pero los efectos de ese miedo se hacen notar más allá de los animales. Los animales son criaturas adaptables. Se adaptan a nuestros horarios y comportamientos modificando los suyos propios. Y estos cambios en sus comportamientos tienen consecuencias. Los efectos ecológicos de estos cambios se extienden hasta los grandes carnívoros, como los pumas.

Los pumas viven a lo largo de las Américas, desde la Patagonia en el sur hasta las regiones sub-árticas de Canadá. Pero la mayoría de la gente que vive en esos lugares pasará todas sus vidas sin ver a un solo puma. Ellos saben cómo evitarnos, y los animales que suelen ser presas de los pumas lo han notado.

Un nuevo artículo publicado en la revista científica Ecosphere ha encontrado que los ciervos de cola negra en las montañas de Santa Cruz de California están pasando más tiempo en las áreas del bosque más cercanas a la habitación humana. Y no es porque las plantas allí sean de mejor calidad o sepan mejor, o porque los humanos les estén dando de comer. Es porque los pumas están asustados de acercarse a estas áreas donde hay gente en las cercanías, y por ello evitan ir a esas áreas.

Los pumas están pasando tanto tiempo en esas áreas de los bosques que los están modificando. Las plantas en estas áreas se están volviendo más arbustivas, ya que los ciervos están básicamente podando las plantas. Esto, a su vez, crea más comida para los ciervos, creando un escenario ideal para los ciervos. Necesitamos más investigación para saber cómo estos cambios afectan a otros animales en estas áreas, como los pájaros o los insectos, pero el efecto indirecto que la presencia de los humanos ha causado en el paisaje está claro.

## Blue light glasses help some people sleep, but they don't reduce digital eye strain

If your eyes hurt from staring at screens during the pandemic, you are not alone

Neuroscience

University of Pennsylvania

In every “Things you need to buy from Amazon!” list, you will almost always find one item: blue light-blocking glasses. At the height of the COVID-19 pandemic, we irradiated our eyes with blue light — by staring at smartphones, televisions, and computers far more often and for longer periods than we did during pre-pandemic times. Suddenly, people started eyeing light-blocking glasses to reduce eye strain. But do these glasses actually help, or are they just a scam?

At first glance, whittling down our exposure to blue light makes scientific sense. Blue light is critical in maintaining our circadian rhythms, which are the natural cycles our body goes through in a 24-hour period that dictate waking and sleeping. But timing is key in the way blue light controls our bodies. During the day, blue light activates the parts of our brain required for attention; at night, however, it blocks the production of melatonin, a molecule that induces sleep, and increases alertness.

This is why some researchers have used blue light-blocking glasses to see whether they can improve sleep quality. Studies have found that blue light-blocking glasses improved sleep in people with Parkinson’s disease, delayed sleep disorder, and insomnia. In fact, the use of blue light glasses promotes advanced sleep onset and melatonin production, suggesting that they could indeed be helpful in regulating sleep.

However, this may not hold for individuals without sleep disturbances. An analysis of many studies found that blue light-blocking glasses did not improve sleep quality for the general population. It’s possible that these glasses only benefit individuals who already have some type of sleep disorder.

Furthermore, blue light glasses can't reduce digital eye strain — characterized by dry eyes, headaches, and blurred vision —  because it has nothing to do with blue light exposure. Mark Rosenfield, one of the researchers who debunked such advertising of glasses sellers, suggests instead taking breaks often and increasing the viewing distance to reduce digital eye strain.

Whether blue light-blocking glasses help the rest of the population and how still remain to be studied. So, while these glasses may improve sleep quality for some, it will be just as necessary to reduce our exposure to digital devices as much as we can. So, if you need an excuse to decline yet another Zoom meeting, consider your eyes!

## Researchers find the molecules in burning trees that cause — and suppress — health problems

Not all trees are created equal

Chemistry

University of Illinois at Urbana-Champaign

Exposure to smoke in the areas around wildfire-prone forests is known to exacerbate respiratory and cardiovascular disease. However, surprisingly little is known about the exact mechanism by which this occurs. This is in part due to the complex nature of chemical reactions that occur as forests burn: Plants and trees are sophisticated living systems, and when they are subjected to the massive amount of heat in a fire, chemical reactions run wild, creating a myriad of combustion products.

Shedding light on this issue requires tracking not just individual chemicals but the interplay between mixtures of chemicals. For example, chemical X might affect our lungs in one way by itself but in another way when accompanied by chemical Y. In a new study published in Science of the Total Environment, environmental scientists from the University of North Carolina analyzed the smoke of five commonly burned biomass components (eucalyptus, peat, pine, pine needles, and red oak). They identified at least 86 different chemicals that could be released when those materials burn.

By tracking the relationships between these chemicals, the researchers discovered that the degree of toxicity of wildfire smoke depends on the type of biomass being burned, with pine being one of the least harmful. This is primarily due to the presence of a class of molecules called methoxyphenols, including vanillin (which gives vanilla its flavor). Even when harmful inorganic or ionic components like lead, chlorine, or phosphates were present in high amounts, methoxyphenols acted as protective agents, suppressing the negative effects. This can be helpful not only to identify which people living nearby are most at risk based on the composition of nearby biomass, but also to give clues to how adverse effects could be mitigated by a mindful selection of trees for reforestation.

## A psychedelic experience may not be required to benefit from psilocybin

Recent research smooths the path toward at-home psilocybin treatment for neurological conditions

Neuroscience

University of Washington

It’s widely believed that the now-undeniable therapeutic properties of psilocybin, the chemical found in magic mushrooms, are due to its hallucinogenic, consciousness-warping properties. Psilocybin and other psychedelics are extremely effective in treating a host of neurological conditions, from clinical depression to migraine  —  just one dose can make people feel less depressed for up to six months

But the features that make magic mushrooms a popular recreational drug (the six-plus hours of visual hallucinations, the altered state of consciousness), lower its clinical usability. Essentially, though psilocybin is largely benign, patients need to be observed and counseled for their trips. But contrary to conventional wisdom, or what your very chill, Burning man-going friend will tell you, the altered consciousness state may not be necessary for the beneficial effects of psilocybin.

A recent study published in the journal PNAS showed that psilocybin still decreases depressive symptoms in mice even when it’s delivered alongside a drug that prevents psilocybin’s hallucinatory effects.  This means that in the future, people may be able to reap the beneficial effects of psilocybin from the comforts of their own homes — without things getting weird.

## Fruit flies have more sex when predatory wasps come around

This weird predator-prey interaction appears to be reliant on one gene in particular

Genetics

Louisiana State University

Predator-prey interactions are like an arms race, with both parties trying to one up each other to survive. Animals have developed many ingenious ways to escape predation, such as by startling, confusing, or actively repelling their predators.

Typically, when an animal notices its predator lurking around, it either pauses its routine to run away from the predator or tries a defensive tactic to ward it off. That is why scientists were puzzled to see what fruit flies (Drosophila melanogaster) do when predatory wasps are nearby: they increase their mating. This finding is detailed in a new paper published in Nature Communications

Since wasps specifically target fruit fly larvae, the accelerated mating made no sense to the researchers. They started by checking whether the increased mating was a result of changes in male or female flies or a combination of both. To resolve this, they paired off females and males exposed to wasps with both exposed and unexposed partners. It turned out that, wasp exposure was making only the female flies more interested in mating — males exposed to wasps weren’t observed to be more interested than unexposed males. Turning their focus solely on the females, researchers then used mutant fly strains with impaired hearing and vision to confirm that seeing the wasp was essential for heightened mating response.

These initial observations led the researchers to question the nature of the response to wasps — was it immediate or lasting? They introduced a gap of two hours between wasp-exposure and mating, to test out the possible timespan of this response. They saw that the response was indeed temporary. Exposed flies mated as usual if enough time elapsed after being around the wasps.

Upon comparing gene expression profiles of wasp-exposed and non-exposed flies, researchers were able to identify ten genes that showed high expression levels only in wasp-exposed flies. Among them, the IBIN gene showed highest increase. When they gave flies a mutated copy of IBIN gene, those flies didn't show that accelerated mating behavior near wasps.

The researchers propose that female flies probably prioritize successful mating over finding a suitable mate, because they anticipated the additional effort required for finding a safe egg-laying sites when surrounded by the wasps.

## People exposed to Chernobyl's radiation don't pass mutations to their children

The largest-ever study brings welcome news to people who survived the 1986 disaster

Johns Hopkins University

The Chernobyl nuclear disaster of 1986 exposed millions of Ukrainian people to high levels of ionizing radiation. This type of radiation is known to increase DNA mutation rates and animal studies have suggested that parents exposed to ionizing radiation produce offspring who have higher-than-normal levels of DNA mutations. However, whether this occurs in humans has remained largely unknown. Studies that have tried to answer this question before have lacked sufficiently large sample sizes and defined radiation exposure levels in the parents to answer the question conclusively.

A new study published in Science is the largest ever, and the first to sequence the entire genomes of parent/children trios to determine the full impact of radiation exposure on the next generation. Researchers interviewed Ukrainian parents about their exposure in the wake of the Chernobyl disaster and calculated cumulative radiation dose estimates for each person. They then sequenced DNA samples from over 100 exposed parent/child trios and calculated the parents' mutation rates, as well as the number of new mutations in the children. According to their analysis, there is no relationship between the number of new mutations in children's DNA and radiation exposure level of their parents.

The finding comes as a relief for victims of the Chernobyl accident, and brings much needed hope to others who have experienced nuclear disasters. Survivors of nuclear incidents have not only suffered debilitating health consequences, but intense stigma from their communities. Women in particular have been shunned by potential partners due to fears that their children would inherit genetic defects, and in the immediate wake of the disaster it is estimated that tens of thousands of women intentionally terminated their pregnancies due to this same fear. The results of this study are therefore incredibly significant for the individuals and communities that have been ravaged by man-made nuclear disasters.

## "Spatially resolved transcriptomics" takes a snapshot of gene expression in our brains

This approach was deemed 2020's Method of the Year

Neuroscience

McGill University

“Spatially resolved transcriptomics” was the “Method of the Year 2020” according to Nature Methods. But what is this technology, and what can we do with it? A recent study from the Lieber Institute for Brain Development provides an example.

First, a thin slice of biological tissue is placed on a specialized microscope slide. The tissue slice is photographed under the microscope. RNA molecules within the tissue are captured and sequenced to measure gene expression. The microscope photo helps determine which genes were expressed in specific parts of the tissue slice, revealing how gene expression varies across the tissue.

The approach is suitable for studying the human brain, especially the cerebral cortex which is organized into well-defined layers. Each layer has its own specific types of cells with a distinctive shape, molecular identity, and connectivity with the rest of the brain. Earlier studies measured the gene expression in layers of the cortex one gene at a time. In contrast, the recent study from the Lieber Institute measured layer-specific expression across all expressed genes, called the “transcriptome”.

Using brain tissue from three donors, the researchers measured gene expression across the layers of the prefrontal cortex – a brain region implicated in psychiatric and neurological diseases. They confirmed the previously described layer-specific expression pattern of several genes and identified additional genes which also show a layered pattern of expression. Further, the researchers found layer-specific expression of genes linked with schizophrenia and autism, a finding that could enhance our understanding of the mechanisms underlying these disorders.

The results of the study were made freely available to the community, representing a valuable resource for the many researchers who will undoubtedly apply this technology to further explore human cortical gene expression in the near future.

## Mathematicians hope digital "proof assistants" will fix the field's own replication crisis

Computer programs can be better than humans, but they're not perfect

Mathematics

Freelance

While it’s tempting to think that math is a discipline free from mistakes, the reality is quite different.  Published proofs have been found to contain errors and, worryingly, modern proofs are sometimes so long and complicated that it’s difficult for mathematicians to check that they are correct. (A proof, in mathematics, is a step-by-step logical argument that asserts some conclusion about a mathematical statement.)

In a recent article published in the journal The Mathematics Intelligencer, Cambridge mathematician Anthony Bordg compared this situation to the replication crisis in science. According to his analogy, attempts to check the correctness of a proof are like attempts to replicate a scientific experiment.  If everything is correct, the proof has been replicated.  But if an error is found or if mathematicians cannot determine whether the proof is correct for some other reason, then the attempt to replicate the proof has failed.

But too many proofs cannot be replicated.  So, what can we do to fix this?

One potential solution is to use computers during the peer review process.  Software called proof assistants can check if a proof is correct, once the proof has been translated into a language the software understands.  While human reviewers do not always rigorously check that every single inference in a proof is correct, a proof assistant does. And if it finds anything amiss, it will complain. A proof assistant's blessing therefore counts as a successful replication of the proof “once and for all.”

But mathematicians have not yet welcomed proof assistants with open arms.  One problem is that they are not exactly user friendly, and Bordg acknowledges that there is plenty of room for improvement.  With further development, proof assistants will hopefully become more widely used in the near future.