evolution

Tiny, long-armed dinosaur leads to rethink of dinosaur miniaturization

Biology, dinosaurs, evolution, paleontology, Science / Tim Belzer / March 8, 2026

Small size seems to have come before a change in diet for a tiny dinosaur lineage.

Alvarezsaurids were mostly small-bodied theropods that paleontologists originally misinterpreted as early flightless birds, only to later recognize them as an ant-eating lineage of non-avian dinosaurs. For years, we suspected that Alvarezsaurids underwent a rare process of evolutionary miniaturization directly coupled to a diet of social insects like ants and termites. It was a tidy hypothesis: They got smaller to become more efficient at catching ants.

Now, a recently discovered fossil of one of the smallest alvarezsaurids ever found suggests that the evolution of miniature dinosaurs likely wasn’t as neat and linear as we thought. This new species, called Alnashetri cerropoliciensis, probably did not feed on ants at all. “It was a pursuit predator actively hunting insects and small mammals,” said Peter Makovicky, a paleontologist at the University of Minnesota.

The oddball

Alverezsaurids, found mostly in the Late Cretaceous rocks of Asia and South America, had short forelimbs tipped with a single oversized thumb claw built for digging. They also had minute teeth and sensory adaptations akin to those in modern nocturnal birds—everything necessary to work on termite mounds. “The explanation of their small body size has been tied to this specialization,” Makovicky explained.

The dinosaur he and his colleagues found, however, did not look like a specialized ant-eater.

The fossil of Alnashetri cerropoliciensis was unearthed from the Candeleros Formation at the Cerro Policía locality in Argentina’s Río Negro Province and is estimated to have lived roughly 90 million years ago. It currently stands as the most complete and smallest Alvarezsaurid skeleton found in South America.

While missing its skull roof, parts of its right arm, its lower right leg, and much of its tail, the skeleton preserves plenty of its crucial anatomy. Its bone tissue reveals that the alvarezsaurid was a subadult, likely approaching sexual maturity, as indicated by the presence of what appears to be medullary bone, a temporary tissue associated with egg-laying in modern birds. Despite being nearly fully grown, this dinosaur is estimated to have weighed a mere 700 grams.

The real surprise, though, came when researchers realized that Alnashetri wasn’t a highly specialized, late-stage Alvarezsauroid. Instead, despite living in the Late Cretaceous, it occupied an early-branching position among earlier, basal members of the clade.

This combination of tiny size and early-branching status fundamentally breaks our previous model of how these animals evolved. If the miniaturization of Alvarezsauroids was strictly tied to their lifestyle as stubby-armed insect-eaters, an early-diverging species like Alnashetri should have some transitional features on a steady, clade-wide march toward that extreme endpoint. But it didn’t look that way.

“It’s a very long-limbed animal, so it was probably fairly fast. My best analogy would be something like a roadrunner from the American West,” Makovicky said.

Arms and teeth

Late Alvarezsaurids had tiny, robust forelimbs that were less than half the length of their femurs. Alnashetri, though, sported comparatively long forelimbs that were 61 percent of the length of its entire hindlimb. While it had three-fingered hands with a robust first digit, a hallmark of its group, it still retained slender second and third digits, unlike its later cousins.

Other features that challenge the established evolutionary model of miniature dinosaurs are Alnashetri’s jaws and teeth. Its dentition features non-serrated teeth set into sockets, but importantly, these teeth are not extremely small, as they were in the late Alvarezsaurids like Shuvuuia or Jaculinykus. “This decoupled the evolution of small body size from anatomical specializations,” Makovicky explained.

The team concluded that extreme miniaturization in Alvarezsaurids did not necessarily co-evolve with either the evolution of smaller arms more suitable for digging or small teeth built for crushing ants and/or termites. Instead of a clade-wide trend where the entire lineage steadily shrank over time, a new evolutionary model that includes Alnashetri suggests that Alvarezsaurid body mass fluctuated repeatedly. Alnashetri, it turns out, achieved its 700-gram frame independently from the other, highly specialized alvarezsaurid species.

But Alnashetri didn’t just upend the understanding of how Alvarezsaurids evolved their tiny bodies. It also redrew the map of where they lived.

Museum tour

Before Makovicky’s study, it was a mystery why Alvarezsaurids were found almost exclusively in the late Cretaceous rocks of Asia and South America. The previous leading hypothesis suggested that the group must have dispersed back and forth between these two landmasses relatively late in the game. But placing Alnashetri, a remarkably basal member, into their evolutionary tree created a massive ghost lineage. The phylogenetic analysis linked geographically close South American species to much older, geologically distant Asian taxa like Bannykus and Xiyunykus, implying that the group must have diverged way back in the Jurassic period.

To explain this chronological and geographic gap, Makovicky and his colleagues started digging through historical museum collections to see if early Alvarezsaurids had been hiding there under different names. It turned out they had.

The team successfully reidentified a small, fragmentary theropod from the Upper Jurassic Morrison Formation in North America, as well as a Lower Cretaceous taxon from the Isle of Wight in Europe. These were early, diverging Alvarezsaurids, and they possessed distinct features such as specialized ball-and-socket joints in the neck vertebrae that are unique in the Alvarezsaurid clade. These museum reidentifications entirely changed the biogeographical story.

If Alvarezsaurids were roaming North America and Europe in the Jurassic and Early Cretaceous, they weren’t just performing a late-stage migration between Asia and South America. Instead, the new model proposed by Makovicky and his team reconstructs a widespread Pangaean distribution. Early Alvarezsaurids were likely present across the globe before the supercontinent Pangaea fully fractured.

The Late Cretaceous distributions we see in the fossil record today would therefore be the result of populations slowly becoming isolated as the continents drifted apart, combined with regional extinctions that wiped them out in places like North America and Europe. The populations in Asia and South America represent surviving pockets.

Still, Makovicky’s work produced far more questions than answers. If at least some Alvarezsaurids did not evolve their miniature bodies as an adaptation to eating ants, what made them so small?

Messy evolution

“We sort of falsified this nice narrative where Alvarezsaurid body size change was driven by ecology, but unfortunately, we don’t have anything good to replace it,” Makovicky acknowledged.

The classic story of Alvarezsaurids—a lineage steadily shrinking in lockstep as it committed to a life of termite-hunting, finally migrating across the Late Cretaceous globe—was neat and logical, but it’s apparently gone now. “That’s science. Sometimes you can falsify a hypothesis without necessarily finding a better one to support,” Makovicky added. But his team is already busy looking for evidence documenting the new, more complex and messier version of Alvarezsaurid evolutionary history. “We have a couple of angles we’re pursuing,” he said.

The first involves taking a closer look at Alnashetri’s anatomy using CT scans. The goal here is to treat Alnashetri as a starting point to understand the stepwise evolution of its ant-eating, specialized cousins. Most of this meticulous scanning is currently happening in Argentina. The second angle, though, seems way more thrilling. “By pure luck, we found another Alvarezsaur in the same general area,” Makovicky said.

The other Alvarezsaur is bigger than Alnashetri and has slightly shorter forelimbs. “It’s still being prepared, but I think it will sort of give us the next chapter in the story of how Alvarezsaurids evolved,” Makovicky explained. “It’s probably a few years out in the making.”

Makovicky’s work on Alnashetri is published in Nature: https://doi.org/10.1038/s41586-026-10194-3

Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.

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A unicorn-like Spinosaurus found in the Sahara

Biology, dinosaurs, evolution, paleontology, Science, spinosaurus / Tim Belzer / March 7, 2026

A unique head spike and fish-eating jaws help make sense of these dinosaurs.

The Spinosaurus is a sail-backed, crocodile-snouted dinosaur that Hollywood depicted as a giant terrestrial predator capable of taking down a T. rex in Jurassic Park 3. Then they changed their mind and made it a fully aquatic diver in Jurassic World Rebirth—a rendering that was more in line with the latest paleontological knowledge.

But now, deep in the Sahara Desert, a team of researchers led by Paul C. Sereno, a paleontologist at the University of Chicago, discovered new Spinosaurus fossils suggesting both scientists and filmmakers might have got it all wrong again. The Spinosaurus most likely wasn’t an aquatic diver because, apparently, it couldn’t dive.

Bones in the sand

While the T. rex-beating version of the Spinosaurus was considered unlikely due to its relatively fragile skull, the newer depiction as an aquatic diver made more sense in light of paleontological evidence. Until now, all remains of these predators were pulled from coastal deposits near ancient seas and oceans. That geographic distribution was consistent with the aquatic lifestyle interpretation. If a creature lived on the coast, maybe it swam out to sea like a prehistoric seal, only crawling out to the beaches to rest just as it was depicted in Jurassic World Rebirth.

But the Spinosaurus found by Sereno and his colleagues lived in a completely different neighborhood. The fossils were discovered in the central Sahara of Niger, in what was a terrestrial area called Jenguebi. “When you want to find something really, truly new, you have to go where few have been or maybe nobody has been,” Sereno says. “In the case of Jenguebi, I don’t think it’s seen a paleontologist before.” His team managed to find the site, led by local Tuareg guides after driving for over a day and half through the desert. “We had a team of nearly 100, including paleontologists, filmmakers, guides, and 64 armed guards. You feel like you’re in an Indiana Jones movie,” Sereno recalls. But the effort paid off.

Back in the Cenomanian stage of the Late Cretaceous, the Jenguebi was an inland basin laced with rivers—a riparian habitat situated between 500 and 1,000 kilometers away from the nearest marine shoreline. In these riverbank sediments, Sereno and his team unearthed multiple specimens of the new Spinosaurus species they called S. mirabilis. The skeletons were buried right alongside massive, long-necked dinosaurs, including various species of titanosaurian and rebbachisaurid sauropods. To Sereno, the proximity of these bones left no doubt that the animals they belonged to lived and died together in the same inland freshwater environment. And this inland existence drives a pretty big nail in the coffin of the aquatic diver idea.

Prehistoric heron

The researchers point out that all large-bodied secondarily aquatic tetrapods like whales, mosasaurs, or plesiosaurs, are marine. Finding a giant Spinosaurus thriving in an inland river system strongly supports the idea that it was a semiaquatic, shoreline ambush predator that would wade into shallow waters like a giant crane or heron. But there were other hints that the Spinosaurus was not a diver.

“When you calculate this animal’s lung volume and the air that was permanently in its bones, you’ll find out it was buoyant,” Sereno explains. The permanent air sacks in the bones, an anatomical feature shared by many modern birds, most likely kept the Spinosaurus afloat even when it exhaled all the air out of its lungs. “Birds that dive get rid of those air sacks—penguins got rid of them,” Sereno says. “It’s a balloon you can’t fight against.” He added that even its limbs were far too long to be effectively used as paddles.

This wading lifestyle, the team argues in the paper, was not something unique to the S. mirabilis but extended to other Spinosaurus species as well—the skeletal features of the newly discovered S. mirabilis were found fundamentally similar to its shoreline cousins like S. aegyptiacus on which the Jurassic World Rebirth vision was largely based. Sereno argues it’s highly unlikely that one was a wading river monster while the other was a deep-diving pursuit predator with limited land mobility.

But there was one thing that made S. mirabilis different from S. aegyptiacus. The word “mirabilis” in the newly discovered Spinosaurus’ name translates to “astonishing” in Latin. What Sereno’s team found so astonishing was the prominent crest atop the animal’s head, one of the largest we’ve ever discovered.

The scimitar crown

Instead of the bumpy, fluted ridge seen on S. aegyptiacus, S. mirabilis sported a blade-shaped, scimitar-like bony crest that arched upward and backward from its snout, reaching an apex high over its eyes. This structure was composed of solid bone, unlike the highly porous, pneumatic casques found on some modern birds. However, the bone itself was etched with fine longitudinal striations and deep grooves, indicating that the bony core was just the foundation.

The newly discovered skull, along with a model of what its spike might have looked like on a living animal. Credit: UChicago Fossil Lab

In a living S. mirabilis, this crest would have been enveloped and substantially extended by a keratinous sheath, much like the vibrant growth developed by modern helmeted guinea fowls. If scaled up to a fully mature adult, the bony core alone would measure around 40 centimeters in length; with its keratinous sheath, it could have easily exceeded half a meter. For Sereno, the purpose of this “astonishing” scimitar crown was similar to crests worn today by cranes and herons. “It was asymmetrical. It varied between individuals. So, I think it was solely for display,” Sereno explains.

His team hypothesizes that visual signaling was the primary function of both the cranial crests and the massive trunk and tail sails that define spinosaurids. In the crowded shoreline and riverbank habitats, a towering, brightly colored crest or sail would be an excellent way to broadcast your size, maturity, and genetic fitness to rivals and potential mates without having to engage in a costly physical brawl.

Still, when it came down to it, S. mirabilis, weighing in at well over 7 tons, totally could brawl. “The Spinosaurus was enormous. I think it could have eaten anything it wanted even though its mainstay was fish,” Sereno says.

Crocodile jaw

The showpiece on its forehead aside, the S. mirabilis was a highly specialized killing machine. Its snout featured a low profile with parallel dorsal and ventral margins, terminating in a mushroom-shaped expansion at the tip. The upper and lower jaws allowed the teeth to interdigitate perfectly—there was a notable diastema, a gap in the upper row of teeth, that neatly accommodated the large teeth of the lower jaw. The S. mirabilis jaw structure appears similar to that of modern long-snouted crocodiles, optimized for snatching and snaring aquatic prey with a rapid, trap-like closure. Surprisingly, S. mirabilis showed greater spacing between the teeth in the posterior half of its snout compared to S. aegyptiacus despite being otherwise nearly identical.

Analysis of the animals’ overall body proportions led Sereno and his colleagues to suspect these dinosaurs resided in the functional middle ground between semiaquatic waders like herons and aquatic divers like darters, placing them in an ecological niche entirely separate from all other predatory theropods. Based on Sereno’s paper, the evolutionary history of the spinosaurids started in the Jurassic, when their ancestors first evolved that distinctive, elongate, fish-snaring skull before splitting into two main lineages: baryonychines and spinosaurines.

Then, during the Early Cretaceous, the spinosaurines enjoyed a golden age, diversifying across the margins of the Tethys Sea, a late Paleozoic ocean situated between the continents of Gondwana and Laurasia, to become the dominant predators in their respective ecosystems. What most likely brought an end to their reign was climate change.

The end of the line

The final chapter in the Spinosaurus history played out just before the Late Cretaceous, as the Atlantic Ocean was opening up. This is when spinosaurines, limited geographically to what today is Northern Africa and South America, pushed their biological limits, attaining their maximum body sizes as highly specialized shallow-water ambush hunters. This specialization, though, probably led to their extinction.

Around 95 million years ago, at the end of the Cenomanian stage, the world started to shift. An abrupt rise in global sea levels driven by climate changes drowned the low-lying continental basins and created the Trans-Saharan seaway. The complex, shallow river systems and coastal swamps that supported giant wading spinosaurines vanished beneath the waves. “We don’t see spinosaurid fossil records beyond this period,” Sereno explains. The spinosaurid lineage, unable to dive and adapt to more aquatic lifestyles, was brought to an end.

But we still don’t know much about its beginning. “This is going to be the subject of our next paper—where did the Spinosaurus come from?” Sereno says.

Sereno’s paper on the S. mirabilis is published in Science: https://doi.org/10.1126/science.adx5486

Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.

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Why are vertebrate eyes so different from those of other animals?

Biology, evolution, eyes, Science / Kris Guyer / March 7, 2026

“We think that in this early deuterostome, the median eye contained both ciliary and rhabdomeric cells,” Kafetzis explains. As a result, both cellular lineages were incorporated into a single, ancient, cyclopean eye, which later evolved into the vertebrate eyes.

The vertebrate third eye

A trace of this transformation may still survive in the pineal complex at the base of the brain—often referred to as a vertebrate “third eye.” Scientists have long recognized striking similarities between the retina and the pineal organ, leading many to suspect that the two evolved from a single ancestral structure, with the pineal representing a more rudimentary version.

Kafetzis and his colleagues see it differently.

Many researchers suspect that one class of neurons—the bipolar cells—is unique to the retina and represents a key evolutionary innovation of the vertebrate eye. Bipolar cells connect rods and cones to ganglion cells (hence the name “bipolar”). “We think that these bipolar-like cells already exist in the pineal,” says Kafetzis. “It’s just that they don’t look like the typical bipolar—they don’t have a cell before and a cell after.”

For this reason, Kafetzis and his colleagues argue that bipolar neurons are not a de novo evolutionary invention but instead have a chimeric origin, blending features of both rhabdomeric and ciliary cells and bridging the two photoreceptor lineages.

Though grounded in existing ideas and data, the new proposal offers a potentially far-reaching synthesis. Several aspects still require firmer evidence. The idea that the ancestral chordate adopted a burrowing lifestyle remains debated, and the claim that early bilaterians already possessed paired lateral eyes is still speculative.

The authors acknowledge that their model now needs testing. In the paper, they lay out several ways to do so—from molecular comparisons of pineal and retinal cells to developmental studies and broader sampling of eye development across other deuterostome species.

“We want to put forward some literature-based and inspired hypotheses that are testable, and now we can go out and test them,” concludes Kafetzis.

Cell, 2026. DOI: 10.1016/j.cell.2025.12.056

Federica Sgorbissa is a science journalist; she writes about neuroscience and cognitive science for Italian and international outlets.

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Neanderthals seemed to have a thing for modern human women

Biology, evolution, Genomics, human evolution, Neanderthals, Science / Rejus Almole / February 26, 2026

By now, it’s firmly established that modern humans and their Neanderthal relatives met and mated as our ancestors expanded out of Africa, resulting in a substantial amount of Neanderthal DNA scattered throughout our genome. Less widely recognized is that some of the Neanderthal genomes we’ve seen have pieces of modern human DNA as well.

Not every modern human has the same set of Neanderthal DNA, however; different people will, by chance, have inherited different fragments. But there are also some areas, termed “Neanderthal deserts,” where none of the Neanderthal DNA seems to have persisted. Notably, the largest Neanderthal desert is the entire X chromosome, raising questions about whether this reflects the evolutionary fitness of genes there or mating preferences.

Now, three researchers at the University of Pennsylvania, Alexander Platt, Daniel N. Harris, and Sarah Tishkoff, have done the converse analysis: examining the X chromosomes of the handful of completed genomes we have. It turns out there’s also a strong bias toward modern human sequences there, as well, and the authors interpret that as selective mating, with Neanderthal males showing a strong preference for modern human females and their descendants.

What type of selection are we looking at?

Given how long modern humans and Neanderthals had been evolving as separate populations, some degree of genetic incompatibility is definitely possible. Lots of proteins interact in various ways, and the genes behind these interaction networks will evolve together—a change in one gene will often lead to compensatory changes in other genes in the network. Over time, those changes may mean re-introducing the original gene will actually disrupt the network, with a negative impact on fitness.

That means the introduction of some Neanderthal genes into the modern human genome (or vice versa) would be disruptive and make carriers of them less fit. So they’d be selected against and lost over the ensuing generations. Of course, some segments would likely be lost at random—the genome’s pretty big, and the modern human population was likely large and growing, allowing its DNA to dilute out the influence of other human populations. Figuring out which influence is dominant can be challenging.

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Dinosaur eggshells can reveal the age of other fossils

Biology, dinosaurs, evolution, paleontology, radioactive dating, Science / Kris Guyer / February 21, 2026

When dinosaur fossils surface at a site, it is often not possible to tell how many millions of years ago their bones were buried. While the different strata of sedimentary rock represent periods of geologic history frozen in time, accurately dating them or the fossils trapped within them has frequently proven to be frustrating.

Fossilized bones and teeth have been dated with some success before, but that success is inconsistent and depends on the specimens. Both fossilization and the process of sediment turning to rock can alter the bone in ways that interfere with accuracy. While uranium-lead dating is among the most widely used methods for dating materials, it is just an emerging technology when applied to directly dating fossils.

Dinosaur eggshells might have finally cracked a way to date surrounding rocks and fossils. Led by paleontologist Ryan Tucker of Stellenbosch University, a team of researchers has devised a method of dating eggshells that reveals how long ago they were covered in what was once sand, mud, or other sediments. That information will give the burial time of any other fossils embedded in the same layer of rock.

“If validated, this approach could greatly expand the range of continental sedimentary successions amenable to radioisotopic dating,” Tucker said in a study recently published in Nature Communications Earth & Environment.

This goes way back

Vertebrates have been laying calcified eggs for hundreds of millions of years (although the first dinosaur eggs had soft shells). What makes fossil eggshells so useful for figuring out the age of other fossils is the unique microstructure of calcium carbonate found in them. The way its crystals are arranged capture a record of diagenetic changes, or physical and chemical changes that occurred during fossilization. These can include water damage, along with breaks and fissures caused by being compacted between layers of sediment. This makes it easier to screen for these signs when trying to determine how old they are.

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From chickens to humans, animals think “bouba” sounds round

Behavioral science, Biology, evolution, language, neurobiology, perception, Science / Rejus Almole / February 19, 2026

Does “bouba” sound round to you? How about “maluma”? Neither are real words, but we’ve known for decades that people who hear them tend to associate them with round objects. There have been plenty of ideas put forward about why that would be the case, and most of them have turned out to be wrong. Now, in perhaps the weirdest bit of evidence to date, researchers have found that even newly hatched chickens seem to associate “bouba” with round shapes.

The initial finding dates all the way back to 1947, when someone discovered that people associated some word-like sounds with rounded shapes, and others with spiky ones. In the years since, that association got formalized as the bouba/kiki effect, received a fair bit of experimental attention, and ended up with an extensive Wikipedia entry.

One of the initial ideas to explain it was similarity to actual words (either phonetically or via the characters used to spell them), but then studies with speakers of different languages and alphabets showed that it is likely a general human tendency. The association also showed up in infants as young as 4 months old, well before they master speaking or spelling. Attempts to find the bouba/kiki effects in other primates, however, came up empty. That led to some speculation that it might be evidence of a strictly human processing ability that underlies our capacity to learn sophisticated languages.

A team of Italian researchers—Maria Loconsole, Silvia Benavides-Varela, and Lucia Regolin—now have evidence that that isn’t true either. They decided to look for the bouba/kiki effect well beyond primates, instead turning to newly hatched chickens, only one or three days old. That may sound a bit odd, but chickens have a key advantage beyond ready availability: unlike a 4-month-old human, newly hatched chicks are fully mobile and able to interact with the world.

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Tiny, 45 base long RNA can make copies of itself

biochemistry, Biology, evolution, origin of life, ribozymes, RNA, Science / Tim Belzer / February 13, 2026

Self-copying RNAs may have been a key stop along the pathway to life.

By base pairing with themselves, RNAs can form complex structures with enzymatic activity. Credit: Laguna Design

There are plenty of unanswered questions about the origin of life on Earth. But the research community has largely reached consensus that one of the key steps was the emergence of an RNA molecule that could replicate itself. RNA, like its more famous relative DNA, can carry genetic information. But it can also fold up into three-dimensional structures that act as catalysts. These two features have led to the suggestion that early life was protein-free, with RNA handling both heredity and catalyzing a simple metabolism.

For this to work, one of the reactions that the early RNAs would need to catalyze is the copying of RNA molecules, without which any sort of heritability would be impossible. While we’ve found a number of catalytic RNAs that can copy other molecules, none have been able to perform a key reaction: making a copy of themselves. Now, however, a team has found an incredibly short piece of RNA—just 45 bases long—that can make a copy of itself.

Finding an RNA polymerase

We have identified a large number of catalytic RNAs (generically called ribozymes, for RNA-based enzymes), and some of them can catalyze reactions involving other RNAs. A handful of these are ligases, which link together two RNA molecules. In some cases, they need these molecules to be held together by a third RNA molecule that base pairs with both of them. We’ve only identified a few that can act as polymerases, which add RNA bases to a growing molecule, one at a time, with each new addition base pairing with a template molecule.

Black on white image showing 3 different enzymatic activities. One links any two nucleic acid strands, the other only links base paired strands, and the third links one base at a time. — Some ligases can link two nucleic acid strands (left), while others can link the strands only if they’re held together by base pairing with a template (center). A polymerase can be thought of as a template-dependent ligase that adds one base at a time. The newly discovered ribozyme sits somewhere between a template-directed ligase and a polymerase. Credit: John Timmer

Obviously, there is some functional overlap between them, as you can think of a polymerase as ligating on one base at a time. And in fact, at the ribozyme level, there’s some real-world overlap, as some ribozymes that were first identified as ligases were converted into polymerases by selecting for this new function.

While this is fascinating, there are a few problems with these known examples of polymerase ribozymes. One is that they’re long. So long, in fact, that they’re beyond the length of the sort of molecules that we’ve observed forming spontaneously from a mix of individual RNA bases. This length also means they’re largely incapable of making copies of themselves—the reactions are slow and inefficient enough that they simply stop before copying the entire molecule.

Another factor related to their length is that they tend to form very complex structures, with many different areas of the molecule base-paired to one another. That leaves very little of the molecule in a single-stranded form, which is needed to make a copy.

Based on past successes, a French-UK team decided to start a search for a polymerase by looking for a ligase. And they limited that search in an important way: They only tested short molecules. They started with pools of RNA molecules, each with a different random sequence, ranging from 40 to 80 bases. Overall, they estimated that they made a population of 10¹³ molecules out of the total possible population of 10²⁴ sequences of this type.

These random molecules were fed a collection of three-base-long RNAs, each linked to a chemical tag. The idea was that if a molecule is capable of ligating one of these short RNA fragments to itself, it could be pulled out using the tag. The mixtures were then placed in a salty mixture of water and ice, as this can promote reactions involving RNAs.

After 11 rounds of reactions and tag-based purification, the researchers ended up with three different RNA molecules that could each ligate three-base-long RNAs to existing molecules. Each of these molecules was subjected to mutagenesis and further rounds of selection. This ultimately left the researchers with a single, 51-base-long molecule that could add clusters of three bases to a growing RNA strand, depending on their ability to base-pair with an RNA template. They called this “polymerase QT-51,” with QT standing for “quite tiny.” They later found that they could shorten this to QT-45 without losing significant enzyme activity.

Checking its function

The basic characterization of QT-45 showed that it has some very impressive properties for a molecule that, by nucleic acid standards, is indeed quite tiny. While it was selected for linking collections of molecules that were three bases long, it could also link longer RNAs, work on shorter two-base molecules, or even add a single base at a time, though this was less efficient. While it worked slowly, the molecule’s active half-life was well over 100 days, so it had plenty of time to get things done before it degraded.

It also didn’t need to interact with any specific RNA sequences to work, suggesting it had a general affinity for RNA molecules. As a result, it wasn’t especially picky about the sequences it could copy.

As you might expect from such a small molecule, QT-45 didn’t tolerate changes to its own sequence very well—nearly the entire molecule was important in one way or another. Tests that involved changing every single individual base one at a time showed that almost all the changes reduced the ribozyme’s activity. There were, however, a handful of changes that improved things, suggesting that further selection could potentially yield additional improvements. And the impact of mutations near the center of the sequence was far more severe, suggesting that region is critical for QT-45’s enzymatic activity.

The team then started testing its ability to synthesize copies of other RNA molecules when given a mixture of all possible three-base sequences. One of the tests included a large stretch in which one end of the sequence base-paired with the other. To copy that, those base pairs need to somehow be pried apart. But QT-45 was able to make a copy, meaning it synthesized a strand that was able to base pair with the original.

It was also able to make a copy of a template strand that would base pair with a small ribozyme. That copying produced an active ribozyme.

But the key finding was that it could synthesize a sequence that base-pairs with itself, and then synthesize itself by copying that sequence. This was horribly inefficient and took months, but it happened.

Throughout these experiments, the fidelity averaged about 95 percent, meaning that, in copying itself, it would make an average of two to three errors. While this means a fair number of its copies wouldn’t be functional, it also means the raw materials for an evolutionary selection for improved function—random mutations—would be present.

What this means

It’s worth taking a moment to consider the use of three-base RNA fragments by this enzyme. On the surface, this may seem a bit like cheating, since current RNA polymerases add sequence one base at a time. But in reality, any chemical environment that could spontaneously assemble an RNA molecule 45 bases long will produce many fragments shorter than that. So in many ways, this might be a more realistic model of the conditions in which life emerged.

The authors note that these shorter fragments may be essential for QT-45’s activity. The short ribozyme probably doesn’t have the ability to enzymatically pry base-paired strands of RNA apart to copy them. But in a mixture of lots of small fragments, there’s likely to be an equilibrium, with some base-paired sequences spontaneously popping open and temporarily base pairing with a shorter fragment. Working with these base-paired fragments is probably essential to the ribozyme’s overall activity.

Right now, QT-45 isn’t an impressive enzyme. But the researchers point out that it has only been through 18 rounds of selection, which isn’t much. The most efficient ribozyme polymerases we have at present have been worked on by multiple labs for years. I expect QT-45 to receive similar attention and improve significantly over time.

Also notable is that the team came up with three different ligases in a test of just a small subset of the possible total RNA population of this size. If that frequency holds, there are on the order of 10¹¹ ligating ribozymes among the sequences of this size. Which raises the possibility that we could find far more if we do an exhaustive search. That suggests the first self-copying RNA might not be as improbable as it seems at first.

Science, 2026. DOI: 10.1126/science.adt2760 (About DOIs).

John is Ars Technica’s science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.

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Looking for friends, lobsters may stumble into an ecological trap

Biology, evolution, groupers, lobsters, ocean science, Science / Kris Guyer / December 30, 2025

The authors, Mark Butler, Donald Behringer, and Jason Schratwieser, hypothesized that these solution holes represent an ecological trap. The older lobsters that find shelter in a solution hole would emit the chemicals that draw younger ones to congregate with them. But the youngsters would then fall prey to any groupers that inhabit the same solution hole. In other words, what is normally a cue for safety—the signal that there are lots of lobsters present—could lure smaller lobsters into what the authors call a “predatory death trap.”

Testing the hypothesis involved a lot of underwater surveys. First, the authors identified solution holes with a resident red grouper. They then found a series of sites that had equivalent amounts of shelter, but lacked the solution hole and attendant grouper. (The study lacked a control with a solution hole but no grouper, for what it’s worth.) At each site, the researchers started daily surveys of the lobsters present, registering how large they were and tagging any that hadn’t been found in any earlier surveys. This let them track the lobster population over time, as some lobsters may migrate in and out of sites.

To check predation, they linked lobsters (both large and small) via tethers that let them occupy sheltered places on the sea floor, but not leave a given site. And, after the lobster population dynamics were sorted, the researchers caught some of the groupers and checked their stomach contents. In a few cases, this revealed the presence of lobsters that had been previously tagged, allowing them to directly associate predation with the size of the lobster.

Lobster traps

So, what did they find? In sites where groupers were present, the average lobster was 32 percent larger than the control sites. That’s likely to be because over two-thirds of the small lobsters that were tethered to sites with a grouper were dead within 48 hours. At control sites, the mortality rate was about 40 percent. That’s similar to the mortality rates for larger lobsters at the same sites (44 percent) or at sites with groupers (48 percent).

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The evolution of expendability: Why some ants traded armor for numbers

ants, Biology, evolution, Science / Tim Belzer / December 19, 2025

“Ants reduce per-worker investment in one of the most nutritionally expensive tissues for the good of the collective,” Matte explains. “They’re shifting from self-investment toward a distributed workforce.”

Power of the collective

The researchers think the pattern they observed in ants reflects a more universal trend in the evolution of societal complexity. The transition from solitary life to complex societies echoes the transition from single-celled organisms to multicellular ones.

In a single-celled organism, a cell must be a “jack-of-all-trades,” performing every function necessary for survival. In a multicellular animal, however, individual cells often become simpler and more specialized, relying on the collective for protection and resources.

“It’s a pattern that echoes the evolution of multicellularity, where cooperative units can be individually simpler than a solitary cell, yet collectively capable of far greater complexity,” says Matte. Still, the question of whether underinvesting in individuals to boost the collective makes sense for creatures other than ants remains open, and it most likely isn’t as much about nutritional economics as it is about sex.

Expendable servants

The study focused on ants that already have a reproductive division of labor, one where workers do not reproduce. This social structure is likely the key prerequisite for the cheap worker strategy. For the team, this is the reason we haven’t, at least so far, found similar evolutionary patterns in more complex social organisms like wolves, which live in packs—or humans with their amazingly complex societies. Wolves and people are both social, but maintain a high degree of individual self-interest regarding reproduction. Ant workers could be made expendable because they don’t pass their own genes—they are essentially extensions of the queen’s reproductive strategy.

Before looking for signs of ant-like approaches to quality versus quantity dilemmas in other species, the team wants to take an even closer look at ants. Economo, Matte, and their colleagues seek to expand their analysis to other ant tissues, such as the nervous system and muscles, to see if the cheapening of individuals extends beyond the exoskeleton. They are also looking at ant genomes to see what genetic innovations allowed for the shift from quality to quantity. “We still need a lot of work to understand ants’ evolution,” Matte says.

Science Advances. 2025. DOI: 10.1126/sciadv.adx8068

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Humans in southern Africa were an isolated population until recently

africa, Biology, evolution, Genetics, Genomics, human evolution, Science / Tim Belzer / December 3, 2025

Collectively, the genetic variants in this population are outside the range of previously described human diversity. That’s despite the fact that the present-day southern African hunter-gatherer populations are largely derived from southern African ancestors.

What’s distinct?

Estimates of the timing of when this ancient south African population branched off from any modern-day populations place the split at over 200,000 years ago, or roughly around the origin of modern humans themselves. But this wasn’t some odd, isolated group; estimates of population size based on the frequency of genetic variation suggest it was substantial.

Instead, the researchers suggest that climate and geography kept the group separate from other African populations and that southern Africa may have served as a climate refuge, providing a safe area from which modern humans could expand out to the rest of the continent when conditions were favorable. That’s consistent with the finding that some of the ancient populations in eastern and western Africa contain some southern African variants by around 5,000 years ago.

As far as genetic traits are concerned, the population looked like pretty much everyone else present at the time: brown eyes, high skin pigmentation, and no lactose tolerance. None of the older individuals had genetic resistance to malaria or sleeping sickness that are found in modern populations. In terms of changes that affect proteins, the most common are found in genes involved in immune function, a pattern that’s seen in many other human populations. More unusually, genes that affect kidney function also show a lot of variation.

So there’s nothing especially distinctive or modern apparent in this population, especially not in comparison to any other populations we know of in Africa at the same time. But they are unusual in that they suggest there was a large, stable, and isolated group from other populations present in Africa at the time. Over time, we’ll probably get additional evidence that fits this population into a coherent picture of human evolution. But for now, its presence is a bit of an enigma, given how often other populations intermingled in our past.

Nature, 2025. DOI: 10.1038/s41586-025-09811-4 (About DOIs).

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AI trained on bacterial genomes produces never-before-seen proteins

AI, bacteria, Biology, Computer science, evolution, Genomics, large language model, Science / Kris Guyer / November 21, 2025

The researchers argue that this setup lets Evo “link nucleotide-level patterns to kilobase-scale genomic context.” In other words, if you prompt it with a large chunk of genomic DNA, Evo can interpret that as an LLM would interpret a query and produce an output that, in a genomic sense, is appropriate for that interpretation.

The researchers reasoned that, given the training on bacterial genomes, they could use a known gene as a prompt, and Evo should produce an output that includes regions that encode proteins with related functions. The key question is whether it would simply output the sequences for proteins we know about already, or whether it would come up with output that’s less predictable.

Novel proteins

To start testing the system, the researchers prompted it with fragments of the genes for known proteins and determined whether Evo could complete them. In one example, if given 30 percent of the sequence of a gene for a known protein, Evo was able to output 85 percent of the rest. When prompted with 80 percent of the sequence, it could return all of the missing sequence. When a single gene was deleted from a functional cluster, Evo could also correctly identify and restore the missing gene.

The large amount of training data also ensured that Evo correctly identified the most important regions of the protein. If it made changes to the sequence, they typically resided in the areas of the protein where variability is tolerated. In other words, its training had enabled the system to incorporate the rules of evolutionary limits on changes in known genes.

So, the researchers decided to test what happened when Evo was asked to output something new. To do so, they used bacterial toxins, which are typically encoded along with an anti-toxin that keeps the cell from killing itself whenever it activates the genes. There are a lot of examples of these out there, and they tend to evolve rapidly as part of an arms race between bacteria and their competitors. So, the team developed a toxin that was only mildly related to known ones, and had no known antitoxin, and fed its sequence to Evo as a prompt. And this time, they filtered out any responses that looked similar to known antitoxin genes.

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The evolution of rationality: How chimps process conflicting evidence

Behavioral science, beliefs, Biology, chimps, evolution, Science / Tim Belzer / November 16, 2025

In the first step, the chimps got the auditory evidence, the same rattling sound coming from the first container. Then, they received indirect visual evidence: a trail of peanuts leading to the second container. At this point, the chimpanzees picked the first container, presumably because they viewed the auditory evidence as stronger. But then the team would remove a rock from the first container. The piece of rock suggested that it was not food that was making the rattling sound. “At this point, a rational agent should conclude, ‘The evidence I followed is now defeated and I should go for the other option,’” Engelmann told Ars. “And that’s exactly what the chimpanzees did.”

The team had 20 chimpanzees participating in all five experiments, and they followed the evidence significantly above chance level—in about 80 percent of the cases. “At the individual level, about 18 out of 20 chimpanzees followed this expected pattern,” Engelmann claims.

He views this study as one of the first steps to learn how rationality evolved and when the first sparks of rational thought appeared in nature. “We’re doing a lot of research to answer exactly this question,” Engelmann says.

The team thinks rationality is not an on/off switch; instead, different animals have different levels of rationality. “The first two experiments demonstrate a rudimentary form of rationality,” Engelmann says. “But experiments four and five are quite difficult and show a more advanced form of reflective rationality I expect only chimps and maybe bonobos to have.”

In his view, though, humans are still at least one level above the chimps. “Many people say reflective rationality is the final stage, but I think you can go even further. What humans have is something I would call social rationality,” Engelmann claims. “We can discuss and comment on each other’s thinking and in that process make each other even more rational.”

Sometimes, at least in humans, social interactions can also increase our irrationality instead. But chimps don’t seem to have this problem. Engelmann’s team is currently running a study focused on whether the choices chimps make are influenced by the choices of their fellow chimps. “The chimps only followed the other chimp’s decision when the other chimp had better evidence,” Engelmann says. “In this sense, chimps seem to be more rational than humans.”

Science, 2025. DOI: 10.1126/science.aeb7565

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