Enlarge/ Human Neuron, Digital Light Microscope. (Photo By BSIP/Universal Images Group via Getty Images)
BSIP/Universal Images Group via Getty Images
“Language is a huge field, and we are novices in this. We know a lot about how different areas of the brain are involved in linguistic tasks, but the details are not very clear,” says Mohsen Jamali, a computational neuroscience researcher at Harvard Medical School who led a recent study into the mechanism of human language comprehension.
“What was unique in our work was that we were looking at single neurons. There is a lot of studies like that on animals—studies in electrophysiology, but they are very limited in humans. We had a unique opportunity to access neurons in humans,” Jamali adds.
Probing the brain
Jamali’s experiment involved playing recorded sets of words to patients who, for clinical reasons, had implants that monitored the activity of neurons located in their left prefrontal cortex—the area that’s largely responsible for processing language. “We had data from two types of electrodes: the old-fashioned tungsten microarrays that can pick the activity of a few neurons; and the Neuropixel probes which are the latest development in electrophysiology,” Jamali says. The Neuropixels were first inserted in human patients in 2022 and could record the activity of over a hundred neurons.
“So we were in the operation room and asked the patient to participate. We had a mixture of sentences and words, including gibberish sounds that weren’t actual words but sounded like words. We also had a short story about Elvis,” Jamali explains. He said the goal was to figure out if there was some structure to the neuronal response to language. Gibberish words were used as a control to see if the neurons responded to them in a different way.
“The electrodes we used in the study registered voltage—it was a continuous signal at 30 kHz sampling rate—and the critical part was to dissociate how many neurons we had in each recording channel. We used statistical analysis to separate individual neurons in the signal,” Jamali says. Then, his team synchronized the neuronal activity signals with the recordings played to the patients down to a millisecond and started analyzing the data they gathered.
Putting words in drawers
“First, we translated words in our sets to vectors,” Jamali says. Specifically, his team used the Word2Vec, a technique used in computer science to find relationships between words contained in a large corpus of text. What Word2Vec can do is tell if certain words have something in common—if they are synonyms, for example. “Each word was represented by a vector in a 300-dimensional space. Then we just looked at the distance between those vectors and if the distance was close, we concluded the words belonged in the same category,” Jamali explains.
Then the team used these vectors to identify words that clustered together, which suggested they had something in common (something they later confirmed by examining which words were in a cluster together). They then determined whether specific neurons responded differently to different clusters of words. It turned out they did.
“We ended up with nine clusters. We looked at which words were in those clusters and labeled them,” Jamali says. It turned out that each cluster corresponded to a neat semantic domain. Specialized neurons responded to words referring to animals, while other groups responded to words referring to feelings, activities, names, weather, and so on. “Most of the neurons we registered had one preferred domain. Some had more, like two or three,” Jamali explained.
The mechanics of comprehension
The team also tested if the neurons were triggered by the mere sound of a word or by its meaning. “Apart from the gibberish words, another control we used in the study was homophones,” Jamali says. The idea was to test if the neurons responded differently to the word “sun” and the word “son,” for example.
It turned out that the response changed based on context. When the sentence made it clear the word referred to a star, the sound triggered neurons triggered by weather phenomena. When it was clear that the same sound referred to a person, it triggered neurons responsible for relatives. “We also presented the same words at random without any context and found that it didn’t elicit as strong a response as when the context was available,” Jamali claims.
But the language processing in our brains will need to involve more than just different semantic categories being processed by different groups of neurons.
“There are many unanswered questions in linguistic processing. One of them is how much a structure matters, the syntax. Is it represented by a distributed network, or can we find a subset of neurons that encode structure rather than meaning?” Jamali asked. Another thing his team wants to study is what the neural processing looks like during speech production, in addition to comprehension. “How are those two processes related in terms of brain areas and the way the information is processed,” Jamali adds.
The last thing—and according to Jamali the most challenging thing—is using the Neuropixel probes to see how information is processed across different layers of the brain. “The Neuropixel probe travels through the depths of the cortex, and we can look at the neurons along the electrode and say like, ‘OK, the information from this layer, which is responsible for semantics, goes to this layer, which is responsible for something else.’ We want to learn how much information is processed by each layer. This should be challenging, but it would be interesting to see how different areas of the brain are involved at the same time when presented with linguistic stimuli,” Jamali concludes.
In the early 2000s, local fossil collector Mohamed ‘Ou Said’ Ben Moula discovered numerous fossils at Fezouata Shale, a site in Morocco known for its well-preserved fossils from the Early Ordovician period, roughly 480 million years ago. Recently, a team of researchers at the University of Lausanne (UNIL) studied 100 of these fossils and identified one of them as the earliest ancestor of modern-day chelicerates, a group that includes spiders, scorpions, and horseshoe crabs.
The fossil preserves the species Setapedites abundantis, a tiny animal that crawled and swam near the bottom of a 100–200-meter-deep ocean near the South Pole 478 million years ago. It was 5 to 10 millimeters long and fed on organic matter in the seafloor sediments. “Fossils of what is now known as S. abundantis have been found early on—one specimen mentioned in the 2010 paper that recognized the importance of this biota. However, this creature wasn’t studied in detail before simply because scientists focused on other taxa first,” Pierre Gueriau, one of the researchers and a junior lecturer at UNIL, told Ars Technica.
The study from Gueriau and his team is the first to describe S. abundantis and its connection to modern-day chelicerates (also called euchelicerates). It holds great significance, because “the origin of chelicerates has been one of the most tangled knots in the arthropod tree of life, as there has been a lack of fossils between 503 to 430 million years ago,” Gueriau added.
An ancestor of spiders
The study authors used X-ray scanners to reconstruct the anatomy of 100 fossils from the Fezouata Shale in 3D. When they compared the anatomical features of these ancient animals with those of chelicerates, they noticed several similarities between S. abundantis and various ancient and modern-day arthropods, including horseshoe crabs, scorpions, and spiders.
For instance, the nature and arrangement of the head appendages or ‘legs’ in S. abundantis were homologous with those of present-day horseshoe crabs and Cambrian arthropods that existed between 540 to 480 million years ago. Moreover, like spiders and scorpions, the organism exhibited body tagmosis, where the body is organized into different functional sections.
“Setapedites abundantis contributes to our understandings of the origin and early evolution of two key euchelicerate characters: the transition from biramous to uniramous prosomal appendages, and body tagmosis,” the study authors note.
Currently, two Cambrian-era arthropods, Mollisonia plenovenatrix and Habelia optata are generally considered the earliest ancestors of chelicerates (not all scientists accept this idea). Both lived around 500 million years ago. When we asked how these two differ from S. abundantis, Gueriau replied, “Habelia and Mollisonia represent at best early-branching lineages in the phylogenetic tree. While S. abundantis is found to represent, together with a couple of other fossils, the earliest branching lineage within chelicerates.”
This means Habelia and Mollisonia are relatives of the ancestors of modern-day chelicerates. On the other side, S. abundantis represents the first group that split after the chelicerate clade was established, making it the earliest member of the lineage. “These findings bring us closer to untangling the origin story of arthropods, as they allow us to fill the anatomical gap between Cambrian arthropods and early-branching chelicerates,” Gueriau told Ars Technica.
S. abundantis connects other fossils
The researchers faced many challenges during their study. For instance, the small size of the fossils made observations and interpretation complicated. They overcame this limitation by examining a large number of specimens—fortunately, S. abundantis fossils were abundant in the samples they studied. However, these fossils have yet to reveal all their secrets.
“Some of S. abundantis’ anatomical features allow for a deeper understanding of the early evolution of the chelicerate group and may even link other fossil forms, whose relationships are still highly debated, to this group,” Gueriau said. For instance, the study authors noticed a ventral protrusion at the rear of the organism. Such a feature is observed for the first time in chelicerates but is known in other primitive arthropods.
“This trait could thus bring together many other fossils with chelicerates and further resolve the early branches of the arthropod tree. So the next step for this research is to investigate deeper this feature on a wide range of fossils and its phylogenetic implications,” Gueriau added.
Rupendra Brahambhatt is an experienced journalist and filmmaker. He covers science and culture news, and for the last five years, he has been actively working with some of the most innovative news agencies, magazines, and media brands operating in different parts of the globe.
The basic outline of the interactions between modern humans and Neanderthals is now well established. The two came in contact as modern humans began their major expansion out of Africa, which occurred roughly 60,000 years ago. Humans picked up some Neanderthal DNA through interbreeding, while the Neanderthal population, always fairly small, was swept away by the waves of new arrivals.
But there are some aspects of this big-picture view that don’t entirely line up with the data. While it nicely explains the fact that Neanderthal sequences are far more common in non-African populations, it doesn’t account for the fact that every African population we’ve looked at has some DNA that matches up with Neanderthal DNA.
A study published on Thursday argues that much of this match came about because an early modern human population also left Africa and interbred with Neanderthals. But in this case, the result was to introduce modern human DNA to the Neanderthal population. The study shows that this DNA accounts for a lot of Neanderthals’ genetic diversity, suggesting that their population was even smaller than earlier estimates had suggested.
Out of Africa early
This study isn’t the first to suggest that modern humans and their genes met Neanderthals well in advance of our major out-of-Africa expansion. The key to understanding this is the genome of a Neanderthal from the Altai region of Siberia, which dates from roughly 120,000 years ago. That’s well before modern humans expanded out of Africa, yet its genome has some regions that have excellent matches to the human genome but are absent from the Denisovan lineage.
One explanation for this is that these are segments of Neanderthal DNA that were later picked up by the population that expanded out of Africa. The problem with that view is that most of these sequences also show up in African populations. So, researchers advanced the idea that an ancestral population of modern humans left Africa about 200,000 years ago, and some of its DNA was retained by Siberian Neanderthals. That’s consistent with some fossil finds that place anatomically modern humans in the Mideast at roughly the same time.
There is, however, an alternative explanation: Some of the population that expanded out of Africa 60,000 years ago and picked up Neanderthal DNA migrated back to Africa, taking the Neanderthal DNA with them. That has led to a small bit of the Neanderthal DNA persisting within African populations.
To sort this all out, a research team based at Princeton University focused on the Neanderthal DNA found in Africans, taking advantage of the fact that we now have a much larger array of completed human genomes (approximately 2,000 of them).
The work was based on a simple hypothesis. All of our work on Neanderthal DNA indicates that their population was relatively small, and thus had less genetic diversity than modern humans did. If that’s the case, then the addition of modern human DNA to the Neanderthal population should have boosted its genetic diversity. If so, then the stretches of “Neanderthal” DNA found in African populations should include some of the more diverse regions of the Neanderthal genome.
Gaiasia jennyae, a newly discovered freshwater apex predator with a body length reaching 4.5 meters, lurked in the swamps and lakes around 280 million years ago. Its wide, flattened head had powerful jaws full of huge fangs, ready to capture any prey unlucky enough to swim past.
The problem is, to the best of our knowledge, it shouldn’t have been that large, should have been extinct tens of millions of years before the time it apparently lived, and shouldn’t have been found in northern Namibia. “Gaiasia is the first really good look we have at an entirely different ecosystem we didn’t expect to find,” says Jason Pardo, a postdoctoral fellow at Field Museum of Natural History in Chicago. Pardo is co-author of a study on the Gaiasia jennyae discovery recently published in Nature.
Common ancestry
“Tetrapods were the animals that crawled out of the water around 380 million years ago, maybe a little earlier,” Pardo explains. These ancient creatures, also known as stem tetrapods, were the common ancestors of modern reptiles, amphibians, mammals, and birds. “Those animals lived up to what we call the end of Carboniferous, about 370–300 million years ago. Few made it through, and they lasted longer, but they mostly went extinct around 370 million ago,” he adds.
This is why the discovery of Gaiasia jennyae in the 280 million-year-old rocks of Namibia was so surprising. Not only wasn’t it extinct when the rocks it was found in were laid down, but it was dominating its ecosystem as an apex predator. By today’s standards, it was like stumbling upon a secluded island hosting animals that should have been dead for 70 million years, like a living, breathing T-rex.
“The skull of gaiasia we have found is about 67 centimeters long. We also have a front end of her upper body. We know she was at minimum 2.5 meters long, probably 3.5, 4.5 meters—big head and a long, salamander-like body,” says Pardo. He told Ars that gaiasia was a suction feeder: she opened her jaws under water, which created a vacuum that sucked her prey right in. But the large, interlocked fangs reveal that a powerful bite was also one of her weapons, probably used to hunt bigger animals. “We suspect gaiasia fed on bony fish, freshwater sharks, and maybe even other, smaller gaiasia,” says Pardo, suggesting it was a rather slow, ambush-based predator.
But considering where it was found, the fact that it had enough prey to ambush is perhaps even more of a shocker than the animal itself.
Location, location, location
“Continents were organized differently 270–280 million years ago,” says Pardo. Back then, one megacontinent called Pangea had already broken into two supercontinents. The northern supercontinent called Laurasia included parts of modern North America, Russia, and China. The southern supercontinent, the home of gaiasia, was called Gondwana, which consisted of today’s India, Africa, South America, Australia, and Antarctica. And Gondwana back then was pretty cold.
“Some researchers hypothesize that the entire continent was covered in glacial ice, much like we saw in North America and Europe during the ice ages 10,000 years ago,” says Pardo. “Others claim that it was more patchy—there were those patches where ice was not present,” he adds. Still, 280 million years ago, northern Namibia was around 60 degrees southern latitude—roughly where the northernmost reaches of Antarctica are today.
“Historically, we thought tetrapods [of that time] were living much like modern crocodiles. They were cold-blooded, and if you are cold-blooded the only way to get large and maintain activity would be to be in a very hot environment. We believed such animals couldn’t live in colder environments. Gaiasia shows that it is absolutely not the case,” Pardo claims. And this turned upside-down lots of what we knew about life on Earth back in gaiasia’s time.
One of the challenges of working with ancient DNA samples is that damage accumulates over time, breaking up the structure of the double helix into ever smaller fragments. In the samples we’ve worked with, these fragments scatter and mix with contaminants, making reconstructing a genome a large technical challenge.
But a dramatic paper released on Thursday shows that this isn’t always true. Damage does create progressively smaller fragments of DNA over time. But, if they’re trapped in the right sort of material, they’ll stay right where they are, essentially preserving some key features of ancient chromosomes even as the underlying DNA decays. Researchers have now used that to detail the chromosome structure of mammoths, with some implications for how these mammals regulated some key genes.
DNA meets Hi-C
The backbone of DNA’s double helix consists of alternating sugars and phosphates, chemically linked together (the bases of DNA are chemically linked to these sugars). Damage from things like radiation can break these chemical linkages, with fragmentation increasing over time. When samples reach the age of something like a Neanderthal, very few fragments are longer than 100 base pairs. Since chromosomes are millions of base pairs long, it was thought that this would inevitably destroy their structure, as many of the fragments would simply diffuse away.
But that will only be true if the medium they’re in allows diffusion. And some scientists suspected that permafrost, which preserves the tissue of some now-extinct Arctic animals, might block that diffusion. So, they set out to test this using mammoth tissues, obtained from a sample termed YakInf that’s roughly 50,000 years old.
The challenge is that the molecular techniques we use to probe chromosomes take place in liquid solutions, where fragments would just drift away from each other in any case. So, the team focused on an approach termed Hi-C, which specifically preserves information about which bits of DNA were close to each other. It does this by exposing chromosomes to a chemical that will link any pieces of DNA that are close physical proximity. So, even if those pieces are fragments, they’ll be stuck to each other by the time they end up in a liquid solution.
A few enzymes are then used to convert these linked molecules to a single piece of DNA, which is then sequenced. This data, which will contain sequence information from two different parts of the genome, then tells us that those parts were once close to each other inside a cell.
Interpreting Hi-C
On its own, a single bit of data like this isn’t especially interesting; two bits of genome might end up next to each other at random. But when you have millions of bits of data like this, you can start to construct a map of how the genome is structured.
There are two basic rules governing the pattern of interactions we’d expect to see. The first is that interactions within a chromosome are going to be more common than interactions between two chromosomes. And, within a chromosome, parts that are physically closer to each other on the molecule are more likely to interact than those that are farther apart.
So, if you are looking at a specific segment of, say, chromosome 12, most of the locations Hi-C will find it interacting with will also be on chromosome 12. And the frequency of interactions will go up as you move to sequences that are ever closer to the one you’re interested in.
On its own, you can use Hi-C to help reconstruct a chromosome even if you start with nothing but fragments. But the exceptions to the expected pattern also tell us things about biology. For example, genes that are active tend to be on loops of DNA, with the two ends of the loop held together by proteins; the same is true for inactive genes. Interactions within these loops tend to be more frequent than interactions between them, subtly altering the frequency with which two fragments end up linked together during Hi-C.
Enlarge/ Ariel and Caliban learned as kittens that scratching posts were fair game for their natural claw-sharpening instincts.
Sean Carroll
Ah, cats. We love our furry feline overlords despite the occasional hairball and their propensity to scratch the furniture to sharpen their claws. The latter is perfectly natural kitty behavior, but overly aggressive scratching is usually perceived as a behavioral problem. Veterinarians frown on taking extreme measures like declawing or even euthanizing such “problematic” cats. But there are alternative science-backed strategies for reducing or redirecting the scratching behavior, according to the authors of a new paper published in the journal Frontiers in Veterinary Science.
This latest study builds on the group’s prior research investigating the effects of synthetic feline facial pheromones on undesirable scratching in cats, according to co-author Yasemin Salgirli Demirbas, a veterinary researcher at Ankara University in Turkey. “From the beginning, our research team agreed that it was essential to explore broader factors that might exacerbate this issue, such as those influencing stress and, consequently, scratching behavior in cats,” she told Ars. “What’s new in this study is our focus on the individual, environmental, and social dynamics affecting the level of scratching behavior. This perspective aims to enhance our understanding of how human and animal welfare are interconnected in different scenarios.”
The study investigated the behavior of 1,211 cats, with data collected via an online questionnaire completed by the cats’ caregivers. The first section collected information about the caregivers, while the second asked about the cats’ daily routines, social interactions, environments, behaviors, and temperaments. The third and final section gathered information about the frequency and intensity of undesirable scratching behavior in the cats based on a helpful “scratching index.”
The team concluded that there are several factors that influence the scratching behavior of cats, including environmental factors, high levels of certain kinds of play, and increased nocturnal activity. But stress seems to be the leading driver. “Cats might scratch more as a way to relieve stress or mark their territory, especially if they feel threatened or insecure,” said Demirbas. And the top source of such stress, the study found, is the presence of small children in the home.
Enlarge/ A corrugated fiberboard scratching pad can redirect your cat’s unwanted scratching away from the furniture.
Enlarge/ Scientists have observed wound care and selective amputation in Florida carpenter ants.
Florida carpenter ants (Camponotus floridanus) selectively treat the wounded limbs of their fellow ants, according to a new paper published in the journal Current Biology. Depending on the location of the injury, the ants either lick the wounds to clean them or chew off the affected limb to keep infection from spreading. The treatment is surprisingly effective, with survival rates of around 90–95 percent for amputee ants.
“When we’re talking about amputation behavior, this is literally the only case in which a sophisticated and systematic amputation of an individual by another member of its species occurs in the animal kingdom,” said co-author Erik Frank, a behavioral ecologist at the University of Würzburg in Germany. “The fact that the ants are able to diagnose a wound, see if it’s infected or sterile, and treat it accordingly over long periods of time by other individuals—the only medical system that can rival that would be the human one.”
Frank has been studying various species of ants for many years. Late last year, he co-authored a paper detailing how Matabele ants (Megaponera analis) south of the Sahara can tell if an injured comrade’s wound is infected or not, thanks to chemical changes in the hydrocarbon profile of the ant cuticle when a wound gets infected. These ants only eat termites, but termites have powerful jaws and use them to defend against predators, so there is a high risk of injury to hunting ants.
If an infected wound is identified, the ants then treat said wound with antibiotics produced by a special gland on the side of the thorax (the metapleural gland). Those secretions are made of some 112 components, half of which have antimicrobial properties. Frank et al.’s experiments showed that applying these secretions reduced the mortality rate of injured ants by 90 percent, and future research could lead to the discovery of new antibiotics suitable for treating humans. (This work was featured in an episode of a recent Netflix nature documentary, Life on Our Planet.)
Amputation in Camponotus maculatus. Credit: Danny Buffat.
Those findings caused Frank to ponder if the Matabele ant is unique in its ability to detect and treat infected wounds, so he turned his attention to the Florida carpenter ant. These reddish-brown ants nest in rotting wood and can be fiercely territorial, defending their homes from rival ant colonies. That combat comes with a high risk of injury. Florida carpenter ants lack a metapleural gland, however, so Frank et al. wondered how this species treats injured comrades. They conducted a series of experiments to find out.
Frank et al. drew their subjects from colonies of lab-raised ants (produced by queens collected during 2017 fieldwork in Florida), and ants targeted for injury were color-tagged with acrylic paint two days before each experiment. Selective injuries to tiny (ankle-like) tibias and femurs (thighs) were made with sterile Dowel-scissors, and cultivated strains of P. aeruginosa were used to infect some of those wounds, while others were left uninfected as a control. The team captured the subsequent treatment behavior of the other ants on video and subsequently analyzed that footage. They also took CT scans of the ants’ legs to learn more about the anatomical structure.
Enlarge/ Extreme sportsman Ross Edgley comes face to face with a great hammerhead shark in the waters of Bimini in the Bahamas.
National Geographic/Nathalie Miles
Ultra-athlete Ross Edgley is no stranger to pushing his body to extremes. He once ran a marathon while pulling a one-ton car; ran a triathlon while carrying a 100-pound tree; and climbed a 65-foot rope over and over again until he’d climbed the equivalent of Mt. Everest—all for charity. In 2016, he set the world record for the world’s longest staged sea swim around the coastline of Great Britain: 1780 miles over 157 days.
At one point during that swim, a basking shark appeared and swam alongside Edgley for a day and a half. That experience ignited his curiosity about sharks and eventually led to his new National Geographic documentary, Shark vs. Ross Edgley—part of four full weeks of 2024 SHARKFEST programming. Edgley matches his athletic prowess against four different species of shark. He tries to jump out of the water (polaris) like a great white shark; withstand the G forces produced by a hammerhead shark‘s fast, rapid turns; mimic the extreme fasting and feasting regimen of a migrating tiger shark; and match the swimming speed of a mako shark.
“I love this idea of having a goal and then reverse engineering and deconstructing it,” Edgley told Ars. “[Sharks are] the ultimate ocean athletes. We just had this idea: what if you’re crazy enough to try and follow in the footsteps of four amazing sharks? It’s an impossible task. You’re going to fail, you’re going to be humbled. But in the process, we could use it as a sports/shark science experiment, almost like a Trojan horse to bring science and ocean conservation to a new audience.”
And who better than Edgley to take on that impossible challenge? “The enthusiasm he brings to everything is really infectious,” marine biologist and shark expert Mike Heithaus of Florida International University told Ars. “He’s game to try anything. He’d never been in the water with sharks and we’re throwing him straight in with big tiger sharks and hammerheads. He’s loving the whole thing and just devoured all the information.”
That Edgley physique doesn’t maintain itself, so the athlete was up at 4 AM swimming laps and working out every morning before the rest of the crew had their coffee. “I’m doing bicep curls with my coffee cup and he’s doing bicep curls with the 60-pound underwater camera,” Heithaus recalled. “For the record, I got one rep in and I’m very proud of that.” Score one for the shark expert.
(Spoilers below for the various shark challenges.)
Ross vs. the great white shark
Ross Edgley gets some tips on how to power (polaris) his body out of the water like a white shark from synchronized swimmer Samantha Wilson
National Geographic/Nathalie Miles
The Aquabatix synchronized swim team demonstrates the human equivalent to a white shark’s polaris.
National Geographic/Nathalie Miles
Edgley tries out a mono fin to improve his polaris performance.
National Geographic/Nathalie Miles
Edgley propelling 3/4 of his body out of the pool to mimic a white shark’s polaris movement
National Geographic/Bobby Cross
For the first challenge, Edgley took on the great white shark, a creature he describes as a “submarine with teeth.” These sharks are ambush hunters, capable of propelling their massive bodies fully out of the water in an arching leap. That maneuver is called a polaris, and it’s essential to the great white shark’s survival. It helps that the shark has 65 percent muscle mass, particularly concentrated in the tail, as well as a light skeleton and a large liver that serves as buoyancy device.
Edgley, by comparison, is roughly 45 percent muscle mass—much higher than the average human but falling short of the great white shark. To help him try to match the great white’s powerful polaris maneuver, Edgley sought tips on biomechanics from the Aquabatix synchronized swim team, since synchronized swimmers must frequently launch their bodies fully out of the water during routines. They typically get a boost from their teammates to do so.
The team did manage to boost Edgley out of the water, but sharks don’t need a boost. Edgley opted to work with a monofin, frequently used in underwater sports like free diving or finswimming, to see what he could achieve on his own power. After a bit of practice, he succeeded in launching 75 percent of his body (compared to the shark’s 100 percent) out of the water. Verdict: Edgley is 75 percent great white shark.
Ross vs. the hammerhead shark
Edgley vs. a hammerhead shark. He will try to match the animal’s remarkable agility underwater.
National Geographic/Nathalie Miles
A camera team films a hammerhead shark making sharp extreme turns
National Geographic/Nathalie Miles
Edgley prepares to go airborne in a stunt plane to try and mimic the agility of a hammerhead shark in the water.
National Geographic/Nathalie Miles
A standard roll produces 2 g’s, while pulling up is 3 g’s
YouTube/National Geographic
Edgley is feeling a bit queasy.
YouTube/National Geographic
Next up: Edgley pitted himself against the remarkable underwater agility of a hammerhead shark. Hammerheads are known for being able to swim fast and turn on a dime, thanks to a flexible skeleton that enables them to bend and contort their bodies nearly in half. They’re able to withstand some impressive G forces (up to 3 G’s) in the process. According to Heithaus, these sharks feed on other rays and other sharks, so they need to be built for speed and agility—hence their ability to accelerate and turn rapidly.
The NatGeo crew captured impressive underwater footage of the hammerheads in action, including Edgley meeting a 14.7 hammerhead named “Queenie”—one of the largest great hammerheads that visits Bimini in the Bahamas during the winter. That footage also includes shots of divers feeding fish to some of the hammerheads by hand. “They know every shark by name and the sharks know the feeders,” said Heithaus. “So you can safely get close to these big amazing creatures.”
For years, scientists had wondered about the purpose of the distinctive hammer-shaped head. It may help them scan a larger area of the ocean floor while hunting. Like all sharks, hammerheads have sensory pores called ampullae of Lorenzini that allow them to detect electrical signals and hence possible prey. The hammer-shaped head distributes those pores over a wider span.
But according to Heithaus, the hammer shape also operates a bit like the big broad flap of an airplane wing, resulting in excellent hydrodynamics. Moving at high speeds, “You can just tilt the head a tiny bit and bank a huge degree,” he said. “So if a ray turns 180 degrees to escape, the hammerhead can track with it. Other species would take a wider turn and fall behind.”
The airplane wing analogy gave Edgley an idea for how he could mimic the tight turns and high G forces of a hammerhead shark: take a flight in a small stunt plane. The catch: Edgley is not a fan of flying. And as he’d feared, he became horribly airsick during the challenge, even puking into a little airbag at one point. “It looks so cool in the clip,” he said. “But at the time, I was in a world of trouble.” Pilot Mark Greenfield finally cut the experiment short when he determined that Edgley was too sick to continue. Verdict: Edgley is 0 percent hammerhead shark.
Ross vs. the tiger shark
Shark expert Mike Heithaus holds a gelatin shark “lolliop” while Edgley flexes.
National Geographic/Nathalie Miles
Edgley and Heithaus underwater with a tiger shark, tempting it with a gelatin lollipop.
National Geographic/Nathalie Miles
Success! A tiger shark takes a nice big bite.
National Geographic/Nathalie Miles
Edgley flexes with the giant gelatin lollipop with a large bite taken out of it by a tiger shark
National Geographic/Nathalie Miles
Edgley gets his weight and body volume measured in the “Bodpod” before his tiger shark challenge.
National Geographic/Bobby Cross
Edgley fasted and exercised for 24 hours to mimic a tiger shark on a migration route. He dropped 14 pounds.
National Geographic/Nathalie Miles
After all that fasting and exercise, Edgley then gorged himself for 24 hours to put the weight back on. He gained 22 pounds.
National Geographic/Nathalie Miles
The third challenge was trying to match the fortitude of a migrating tiger shark as it makes its way over thousands of miles without food, only feasting at journey’s end. “I was trying to understand the psychology of a tiger shark because there’s just nothing for them to eat [on the journey],” said Ross. And once they arrive at their destination, “they can chow down on entire whale carcasses and eat just about anything. That idea of feast and famine is something we humans used to do all the time. We live quite comfortably now so we’ve lost touch with that.”
The first step was to figure out just how many calories a migrating tiger shark can consume in a single bite. Heithaus has been part of SHARKFEST for several years now and recalled one throwback show, Sharks vs. Dolphins, in which he tried to determine which species of of shark were attacking dolphins, and just how big those sharks might be. He hit upon the idea of making a dolphin shape out of gelatin—essentially the same stuff FIU’s forensic department uses for ballistic tests—and asked his forensic colleagues to make one for him, since the material has the same weight and density of dolphin blubber.
For the Edgley documentary, they made a large gelatin lollipop the same density as whale blubber, and he and Edgley dove down and managed to get an 11-foot tiger shark to take a big 6.2-pound bite out of it. We know how many calories are in whale blubber so Heithaus was able to deduce from that how many calories per bite a tiger shark consumed (6.2 pounds of whale meet is equivalent to about 25,000 calories).
Such field work also lets him gather ever mire specimens of shark bites from a range of species for his research. “The great thing about SHARKFEST is that you’re seeing new, cutting-edge science that may or may not work,” said Heithaus. “But that’s what science is about: trying things and advancing our knowledge even if it doesn’t work al the time, and then sharing that information and excitement with the public.”
Then it was time for Edgley to make like a migrating shark and embark on a carefully designed famine-and-feast regime. First, his weight and body volume were measured in a “Bodpod”: 190.8 pounds and 140.8 pints. Then Edgley fasted and exercised almost continuously for 24 hours with a mix of weight training, running, swimming, sitting in the sauna, and climate chamber cycling. (He did sleep for a few hours.) He dropped 14 pounds and lost twelve pints, ending up at a weight of 177 pounds and a volume of 128.7 pints. Instead of food, what he craved most at the end was water. “When you are in a completely deprived state, you find out what your body actually needs, not what it wants,” said Edgley.
After slaking his thirst, it was time to gorge. Over the next 24 hours, Edgley consumed an eye-popping 35,103 calories in carefully controlled servings. It’s quite the menu: Haribo mix, six liters of Lucozade, a Hulk smoothie, pizza, five slices of lemon blueberry cheesecake, five slices of chocolate mint cheesecake, fish and chips, burgers and fries, two cinnamon loaves, four tubs of Ben & Jerry’s ice cream, two full English breakfasts, five liters of custard, four mars bars, and four mass gainer shakes.
When his weight and volume were measured one last time in the Bodpod, Edgley had regained a whopping 22 pounds for a final weight of 199 pounds. “I wish I had Ross’s ability to eat that much and remain at 0 percent body fat,” said Heithaus. Verdict: Edgley is 28 percent tiger shark.
Ross vs. the mako shark
In 2018, Edgely set the world record for longest assisted sea swim.
National Geographic/Nathalie Miles
Edgley tries to match the speed of a mako shark in the waters of the Menai Strait in Wales.
National Geographic/Nathalie Miles
Finally, Edgley pitted himself against the mighty mako shark. Mako sharks are the speediest sharks in the ocean, capable of swimming at speeds up to 43 MPH. Edgley is a long-distance swimmer, not a sprinter, so he threw himself into training at Loughborough University with British Olympians coaching him. He fell far short of a mako shark’s top speed. The shape of the human body is simply much less hydrodynamic than that of a shark. He realized that despite his best efforts, “I was making up hundredths of a second, which is huge in sprinting,” he said. “That could be the difference between a gold medal at the Paris Olympics and not. But I needed to make up many kilometers per hour.”
So Edgley decided to “think like a shark” and employ a shark-like strategy of riding the ocean currents to increase his speed. He ditched the pool and headed to the Menai Strait in Wales for some open water swimming. Ultimately he was able to hit 10.24 MPH—double what an Olympic swimmer could manage in a pool, but just 25 percent of a mako shark’s top speed. And he managed with the help or a team of 20-30 people dropping him into the fastest tide possible. “A mako shark would’ve just gone, ‘This is a Monday morning, this isn’t an event for me, I’m off,'” said Edgley. Verdict: Edgley is 24 percent mako shark
When the results of all four challenges were combined, Edgley came out at 32 percent overall, or nearly one-third shark. While Edgley confessed to being humbled by his limitations, “I don’t think there’s anyone else out there who could do so as well across the board in comparison,” said Heithaus.
The ultimate goal of Shark vs. Ross Edgley—and indeed all of the SHARKFEST programming—is to help shift public perceptions of sharks. “The great Sir David Attenborough said that the problems facing us in terms of conservation is as much a communication issue as a scientific one,” Edgley said. “The only way we can combat that is by educating people.”
Shark populations have declined sharply by 70 percent or more over the last 50 years. “It’s really critical that we protect and restore these populations,” Heithaus said. Tiger sharks, for instance, eat big grazers like turtles and sea cows, and thus protect the sea grass. (Among other benefits, the sea grass sequesters carbon dioxide.) Sharks are also quite sophisticated in their behavior. “Some have social connections with other sharks, although not to the same extent as dolphins,” said Heithaus. “They’re more than just loners, and they may have personalities. We see some sharks that are more bold, and others that are more shy. There’s a lot more to sharks than we would have thought.”
People who hear about Edgley’s basking shark encounter invariably assume he’d been in danger. However, “We were friends. I’m not on its menu,” Edgley said. “There are so many different species.” He likened it to being chased by a dog. People might assume it was a rottweiler giving chase, when in fact the basking shark is the equivalent of a poodle. “Hopefully what people take away from this is moving from a fear and misunderstanding of sharks to respect and admiration,” Edgley said. “That’ll make the RAF fighter pilot plane worth it.”
And he’s game to take on even more shark challenges in the future. There are a lot more shark species out there, after all, just waiting to go head-to-head with a human ultra-athlete.
Shark vs. Ross Edgley premieres on Sunday, June 30, 2024, on Disney+.
Enlarge/ An artist’s conception of one of the last mammoths of Wrangel Island.
Beth Zaiken
A small group of woolly mammoths became trapped on Wrangel Island around 10,000 years ago when rising sea levels separated the island from mainland Siberia. Small, isolated populations of animals lead to inbreeding and genetic defects, and it has long been thought that the Wrangel Island mammoths ultimately succumbed to this problem about 4,000 years ago.
A paper in Cell on Thursday, however, compared 50,000 years of genomes from mainland and isolated Wrangel Island mammoths and found that this was not the case. What the authors of the paper discovered not only challenges our understanding of this isolated group of mammoths and the evolution of small populations, it also has important implications for conservation efforts today.
A severe bottleneck
It’s the culmination of years of genetic sequencing by members of the international team behind this new paper. They studied 21 mammoth genomes—13 of which were newly sequenced by lead author Marianne Dehasque; others had been sequenced years prior by co-authors Patrícia Pečnerová, Foteini Kanellidou, and Héloïse Muller. The genomes were obtained from Siberian woolly mammoths (Mammuthus primigenius), both from the mainland and the island before and after it became isolated. The oldest genome was from a female Siberian mammoth who died about 52,300 years ago. The youngest were from Wrangel Island male mammoths who perished right around the time the last of these mammoths died out (one of them died just 4,333 years ago).
Enlarge/ Wrangel Island, north of Siberia has an extensive tundra.
Love Dalén
It’s a remarkable and revealing time span: The sample included mammoths from a population that started out large and genetically healthy, went through isolation, and eventually went extinct.
Mammoths, the team noted in their paper, experienced a “climatically turbulent period,” particularly during an episode of rapid warming called the Bølling-Allerød interstadial (approximately 14,700 to 12,900 years ago)—a time that others have suggested might have led to local woolly mammoth extinctions. However, the genomes of mammoths studied through this time period don’t indicate that the warming had any adverse effects.
Adverse effects only appeared—and drastically so—once the population was isolated on that island.
The team’s simulations indicate that, at its smallest, the total population of Wrangel Island mammoths was fewer than 10 individuals. This represents a severe population bottleneck. This was seen genetically through increased runs of homozygosity within the genome, caused when both parents contribute nearly identical chromosomes, both derived from a recent ancestor. The runs of homozygosity within isolated Wrangel Island mammoths were four times as great as those before sea levels rose.
Despite that dangerously tiny number of mammoths, they recovered. The population size, as well as inbreeding level and genetic diversity, remained stable for the next 6,000 years until their extinction. Unlike the initial population bottleneck, genomic signatures over time seem to indicate inbreeding eventually shifted to pairings of more distant relatives, suggesting either a larger mammoth population or a change in behavior.
Within 20 generations, their simulations indicate, the population size would have increased to about 200–300 mammoths. This is consistent with the slower decrease in heterozygosity that they found in the genome.
Long-lasting negative effects
The Wrangel Island mammoths may have survived despite the odds, and harmful genetic defects may not have been the reason for their extinction, but the research suggests their story is complicated.
At about 7,608 square kilometers today, a bit larger than the island of Crete, Wrangel Island would have offered a fair amount of space and resources, although these were large animals. For 6,000 years following their isolation, for example, they suffered from inbreeding depression, which refers to increased mortality as a result of inbreeding and its resulting defects.
That inbreeding also boosted the purging of harmful mutations. That may sound like a good thing—and it can be—but it typically occurs because individuals carrying two copies of harmful mutations die or fail to reproduce. So it’s good only if the population survives it.
The team’s results show that purging genetic mutations can be a lengthy evolutionary process. Lead author Marianne Dehasque is a paleogeneticist who completed her PhD at the Centre for Palaeogenetics. She explained to Ars that, “Purging harmful mutations for over 6,000 years basically indicates long-lasting negative effects caused by these extremely harmful mutations. Since purging in the Wrangel Island population went on for such a long time, it indicates that the population was experiencing negative effects from these mutations up until its extinction.”
Enlarge/ Top row: individual steps in the reaction process. Bottom row: cartoon diagram of the top, showing the position of each DNA and RNA strand.
Hiraizumi, et. al.
While CRISPR is probably the most prominent gene-editing technology, there are a variety of others, some developed before, others since. And people have been developing CRISPR variants to perform more specialized functions, like altering specific bases. In all of these cases, researchers are trying to balance a number of competing factors: convenience; flexibility; specificity and precision for the editing; low error rates; and so on.
So, having additional options for editing can be a good thing, enabling new ways of balancing those different needs. On Wednesday, a pair of papers in Nature describe a DNA-based parasite that moves itself around bacterial genomes through a mechanism that hasn’t been previously described. It’s nowhere near ready for use in humans, but it may have some distinctive features that make it worth further development.
Going mobile
Mobile genetic elements, commonly called transposons, are quite common in many species—they make up nearly half the sequences in the human genome, for example. They are indeed mobile, showing up in new locations throughout the genome, sometimes by cutting themselves out and hopping to new locations, other times by sending a copy out to a new place in the genome. For any of this to work, they need to have an enzyme that cuts DNA and specifically recognizes the right transposon sequence to insert into the cut.
The specificity of that interaction, needed to ensure the system only inserts new copies of itself, and the cutting of DNA, are features we’d like for gene editing, which places a value on better understanding these systems.
Bacterial genomes tend to have very few transposons—the extra DNA isn’t really in keeping with the bacterial reproduction approach of “copy all the DNA as quickly as possible when there’s food around.” Yet bacterial transposons do exist, and a team of scientists based in the US and Japan identified one with a rather unusual feature. As an intermediate step in moving to a new location, the two ends of the transposon (called IS110) are linked together to form a circular piece of DNA.
In its circular form, the DNA sequences at the junction act as a signal that tells the cell to make an RNA copy of nearby DNA (termed a “promoter”). When linear, each of the two bits of DNA on either side of the junction lacks the ability to act as a signal; it only works when the transposon is circular. And the researchers confirmed that there is in fact an RNA produced by the circular form, although the RNA does not encode for any proteins.
So, the research team looked at over 100 different relatives of IS110 and found that they could all produce similar non-protein-coding RNAs, all of which shared some key features. These included stretches where nearby sections of the RNA could base-pair with each other, leaving an unpaired loop of RNA in between. Two of these loops contained sequences that either base-paired with the transposon itself or at the sites in the E. coli genome where it inserted.
That suggests that the RNA produced by the circular form of the transposon helped to act as a guide, ensuring that the transposon’s DNA was specifically used and only inserted into precise locations in the genome.
Editing without precision
To confirm this was right, the researchers developed a system where the transposon would produce a fluorescent protein when it was properly inserted into the genome. They used this to show that mutations in the loop that recognized the transposon would stop it from being inserted into the genome—and that it was possible to direct it to new locations in the genome by changing the recognition sequences in the second loop.
To show this was potentially useful for gene editing, the researchers blocked the production of the transposon’s own RNA and fed it a replacement RNA that worked. So, you could potentially use this system to insert arbitrary DNA sequences into arbitrary locations in a genome. It could also be used with targeting RNAs that caused specific DNA sequences to be deleted. All of this is potentially very useful for gene editing.
Emphasis on “potentially.” The problem is that the targeting sequences in the loops are quite short, with the insertion site targeted by a recognition sequence that’s only four to seven bases long. At the short end of this range, you’d expect that a random string of bases would have an insertion site about once every 250 bases.
That relatively low specificity showed. At the high end, various experiments could see an insertion accuracy ranging from a close-to-being-useful 94 percent down to a positively threatening 50 percent. For deletion experiments, the low end of the range was a catastrophic 32 percent accuracy. So, while this has some features of an interesting gene-editing system, there’s a lot of work to do before it could fulfill that potential. It’s possible that these recognition loops could be made longer to add the sort of specificity that would be needed for editing vertebrate genomes, but we simply don’t know at this point.
Enlarge/ A Sixgill Hagfish (Eptatretus hexatrema) in False Bay, South Africa.
The humble hagfish is an ugly, gray, eel-like creature best known for its ability to unleash a cloud of sticky slime onto unsuspecting predators, clogging the gills and suffocating said predators. That’s why it’s affectionately known as a “snot snake.” Hagfish also love to burrow into the deep-sea sediment, but scientists have been unable to observe precisely how they do so because the murky sediment obscures the view. Researchers at Chapman University built a special tank with transparent gelatin to overcome this challenge and get a complete picture of the burrowing behavior, according to a new paper published in the Journal of Experimental Biology.
“For a long time we’ve known that hagfish can burrow into soft sediments, but we had no idea how they do it,” said co-author Douglas Fudge, a marine biologist who heads a lab at Chapman devoted to the study of hagfish. “By figuring out how to get hagfish to voluntarily burrow into transparent gelatin, we were able to get the first ever look at this process.”
As previously reported, scientists have been studying hagfish slime for years because it’s such an unusual material. It’s not like mucus, which dries out and hardens over time. Hagfish slime stays slimy, giving it the consistency of half-solidified gelatin. That’s due to long, thread-like fibers in the slime, in addition to the proteins and sugars that make up mucin, the other major component. Those fibers coil up into “skeins” that resemble balls of yarn. When the hagfish lets loose with a shot of slime, the skeins uncoil and combine with the salt water, blowing up more than 10,000 times its original size.
From a materials standpoint, hagfish slime is fascinating stuff that might one day prove useful for biomedical devices, or weaving light-but-strong fabrics for natural Lycra or bulletproof vests, or lubricating industrial drills that tend to clog in deep soil and sediment. In 2016, a group of Swiss researchers studied the unusual fluid properties of hagfish slime, specifically focusing on how those properties provided two distinct advantages: helping the animal defend itself from predators and tying itself in knots to escape from its own slime.
Hagfish slime is a non-Newtonian fluid and is unusual in that it is both shear-thickening and shear-thinning in nature. Most hagfish predators employ suction feeding, which creates a unidirectional shear-thickening flow, the better to clog the gills and suffocate said predators. But if the hagfish needs to get out of its own slime, its body movements create a shear-thinning flow, collapsing the slimy network of cells that makes up the slime.
Fudge has been studying the hagfish and the properties of its slime for years. For instance, way back in 2012, when he was at the University of Guelph, Fudge’s lab successfully harvested hagfish slime, dissolved it in liquid, and then “spun” it into a strong-yet-stretchy thread, much like spinning silk. It’s possible such threads could replace the petroleum-based fibers currently used in safety helmets or Kevlar vests, among other potential applications. And in 2021, his team found that the slime produced by larger hagfish contains much larger cells than slime produced by smaller hagfish—an unusual example of cell size scaling with body size in nature.
A sedimentary solution
This time around, Fudge’s team has turned their attention to hagfish burrowing. In addition to shedding light on hagfish reproductive behavior, the research could also have broader ecological implications. According to the authors, the burrowing is an important factor in sediment turnover, while the burrow ventilation changes the chemistry of the sediment such that it could contain more oxygen. This in turn would alter which organisms are likely to thrive in that sediment. Understanding the burrowing mechanisms could also aid in the design of soft burrowing robots.
Enlarge/ Burrowing sequences for a hagfish digging through transparent gelatin.
D.S. Fudge et al., 2024
But first Fudge’s team had to figure out how to see through the sediment to observe the burrowing behavior. Other scientists studying different animals have relied on transparent substrates like mineral cryolite or hydrogels made of gelatin, the latter of which has been used successfully to observe the burrowing behavior of polychaete worms. Fudge et al. opted for gelatin as a sediment replacement housed in three custom transparent acrylic chambers. Then they filmed the gelatin-burrowing behavior of 25 randomly selected hagfish.
This enabled Fudge et al. to identify two distinct phases of movement that the hagfish used to create their u-shaped burrows. First there is the “thrash” stage, in which the hagfish swims vigorously while moving its head from side to side. This not only serves to propel the hagfish forward, but also helps chop up the gelatin into pieces. This might be how hagfish overcome the challenge of creating an opening in the sediment (or gelatin substrate) through which to move.
Next comes the “wriggle” phase, which seems to be powered by an “internal concertina” common to snakes. It involves the shortening and forceful elongation of the body, as well as exerting lateral forces on the walls to brace and widen the burrow. “A snake using concertina movements will make steady progress through a narrow channel or burrow by alternating waves of elongation and shortening,” the authors wrote, and the loose skin of the hagfish is well suited to such a strategy. The wriggle phase lasts until the burrowing hagfish pops its head out of the substrate. The hagfish took about seven minutes or more on average to complete their burrows.
Naturally there are a few caveats. The walls of the acrylic containers may have affected the burrowing behavior in the lab, or the final shape of the burrows. The authors recommend repeating the experiments using sediments from the natural habitat, implementing X-ray videography of hagfish implanted with radio markers to capture the movements. Body size and substrate type may also influence burrowing behavior. But on the whole, they believe their observations “are an accurate representation of how hagfish are creating and moving within burrows in the wild.”
A key aspect of humans’ evolutionary success is the fact that we don’t have to learn how to do things from scratch. Our societies have developed various ways—from formal education to YouTube videos—to convey what others have learned. This makes learning how to do things far easier than learning by doing, and it gives us more space to experiment; we can learn to build new things or handle tasks more efficiently, then pass information on how to do so on to others.
Some of our closer relatives, like chimps and bonobos, learn from their fellow species-members. They don’t seem to engage in this iterative process of improvement—they don’t, in technical terms, have a cumulative culture where new technologies are built on past knowledge. So, when did humans develop this ability?
Based on a new analysis of stone toolmaking, two researchers are arguing that the ability is relatively recent, dating to just 600,000 years ago. That’s roughly the same time our ancestors and the Neanderthals went their separate ways.
Accumulating culture
It’s pretty obvious that a lot of our technology builds on past efforts. If you’re reading this on a mobile platform, then you’re benefitting from the fact that smartphones were derived from personal computers and that software required working hardware to happen. But for millions of years, human technology lacked the sort of clear building blocks that would help us identify when an archeological artifact is derived from earlier work. So, how do you go about studying the origin of cumulative culture?
Jonathan Paige and Charles Perreault, the researchers behind the new study, took a pretty straightforward approach. To start with, they focused on stone tools since these are the only things that are well-preserved across our species’ history. In many cases, the styles of tools remained constant for hundreds of thousands of years. This gives us enough examples that we’ve been able to figure out how these tools were manufactured, in many cases learning to make them ourselves.
Their argument in the paper they’ve just published is that the sophistication of these tools provides a measure of when cultural accumulation started. “As new knapping techniques are discovered, the frontiers of the possible design space expand,” they argue. “These more complex technologies are also more difficult to discover, master, and teach.”
The question then becomes one of when humans made the key shift: from simply teaching the next generation to make the same sort of tools to using that knowledge as a foundation to build something new. Paige and Perreault argue that it’s a matter of how complex it is to make the tool: “Generations of improvements, modifications, and lucky errors can generate technologies and know-how well beyond what a single naive individual could invent independently within their lifetime.”
