evolution

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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World’s oldest RNA extracted from Ice Age woolly mammoth

ancient DNA, ancient RNA, Biology, evolution, Genomics, mammoths, paleontology, Science / Rejus Almole / November 14, 2025

A young woolly mammoth now known as Yuka was frozen in the Siberian permafrost for about 40,000 years before it was discovered by local tusk hunters in 2010. The hunters soon handed it over to scientists, who were excited to see its exquisite level of preservation, with skin, muscle tissue, and even reddish hair intact. Later research showed that, while full cloning was impossible, Yuka’s DNA was in such good condition that some cell nuclei could even begin limited activity when placed inside mouse eggs.

Now, a team has successfully sequenced Yuka’s RNA—a feat many researchers once thought impossible. Researchers at Stockholm University carefully ground up bits of muscle and other tissue from Yuka and nine other woolly mammoths, then used special chemical treatments to pull out any remaining RNA fragments, which are normally thought to be much too fragile to survive even a few hours after an organism has died. Scientists go to great lengths to extract RNA even from fresh samples, and most previous attempts with very old specimens have either failed or been contaminated.

A different view

The team used RNA-handling methods adapted for ancient, fragmented molecules. Their scientific séance allowed them to explore information that had never been accessible before, including which genes were active when Yuka died. In the creature’s final panicked moments, its muscles were tensing and its cells were signaling distress—perhaps unsurprising since Yuka is thought to have died as a result of a cave lion attack.

It’s an exquisite level of detail, and one that scientists can’t get from just analyzing DNA. “With RNA, you can access the actual biology of the cell or tissue happening in real time within the last moments of life of the organism,” said Emilio Mármol, a researcher who led the study. “In simple terms, studying DNA alone can give you lots of information about the whole evolutionary history and ancestry of the organism under study. “Obtaining this fragile and mostly forgotten layer of the cell biology in old tissues/specimens, you can get for the first time a full picture of the whole pipeline of life (from DNA to proteins, with RNA as an intermediate messenger).”

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Dinosaurs may have flourished right up to when the asteroid hit

asteroid, Biology, dinosaurs, evolution, Impact, paleontology, Science / Kris Guyer / October 23, 2025

That seemingly changes as of now, with new argon dating of strata from the Naashoibito Member in the San Juan Basin of present-day New Mexico. Many dinosaur fossils have been obtained from this region, and we know the site differs from the sort of ecosystem found at Hell Creek. But it was previously thought to date back closer to a million years before the mass extinction. The new dates, plus the alignment of magnetic field reversals, tell us that the ecosystem was a contemporary of the one in Hell Creek, and dates to the last few hundred thousand years prior to the mass extinction.

Diverse ecosystems

The fossils at Naashoibito have revealed an ecosystem we now label the “Alamo Wash local fauna.” And they’re fairly distinct from the ones found in Wyoming, despite being just 1,500 kilometers further south. Analyzing the species present using ecological measures, the researchers found that dinosaurs formed two “bioprovinces” in the late Cretaceous—essentially, there were distinct ecosystems present in the northern and southern areas.

This doesn’t seem to be an artifact of the sites, as mammalian fossils seem to reflect a single community across both areas near the mass extinction, but had distinct ecologies both earlier and after. The researchers propose that temperature differences were the key drivers of the distinction, something that may have had less of an impact on mammals, which are generally better at controlling their own temperatures.

Overall, the researchers conclude that, rather than being dominated by a small number of major species, “dinosaurs were thriving in New Mexico until the end of the Cretaceous.”

While this speaks directly to the idea that limited diversity may have primed the dinosaurs for extinction, it also may have implications for the impact of the contemporaneous eruptions in the Deccan Traps. If these were having a major global impact, then it’s a bit unlikely that dinosaurs would be thriving anywhere.

Even with the new data, however, our picture is still limited to the ecosystems present on the North American continent. We do have fossils from elsewhere, but they’re not exactly dated. There are some indications of dinosaurs in the late Cretaceous in Europe and South America, but we don’t have a clear picture of the ecosystems in which they were found. So, while these findings help clarify the diversity of dinosaurs in the time leading up to their extinction, there’s still a lot left to learn.

Science, 2025. DOI: 10.1126/science.adw3282 (About DOIs).

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Fiji’s ants might be the canary in the coal mine for the insect apocalypse

ants, Biology, evolution, Fiji, insects, Science, speciation / Tim Belzer / September 26, 2025

A new genetic technique lets museum samples track population dynamics.

In late 2017, a study by Krefeld Entomological Society looked at protected areas across Germany and discovered that two-thirds of the insect populations living in there had vanished over the last 25 years. The results spurred the media to declare we’re living through an “insect apocalypse,” but the reasons behind their absence were unclear. Now, a joint team of Japanese and Australian scientists have completed a new, multi-year study designed to get us some answers.

Insect microcosm

“In our work, we focused on ants because we have systematic ways for collecting them,” says Alexander Mikheyev, an evolutionary biologist at the Australian National University. “They are also a group with the right level of diversity, where you have enough species to do comparative studies.” Choosing the right location, he explained, was just as important. “We did it in Fiji, because Fiji had the right balance between isolation—which gave us a discrete group of animals to study—but at the same time was diverse enough to make comparisons,” Mikheyev adds.

Thus, the Fijian archipelago, with its 330 islands, became the model the team used to get some insights into insect population dynamics. A key difference from the earlier study was that Mikheyev and his colleagues could look at those populations across thousands of years, not just the last 25.

“Most of the previous studies looked at actual observational data—things we could come in and measure,” Mikheyev explains. The issue with those studies was that they could only account for the last hundred years or so, because that’s how long we have been systematically collecting insect samples. “We really wanted to understand what happened in the longer time frame,” Mikheyev says.

To do this, his team focused on community genomics—studying the collective genetic material of entire groups of organisms. The challenge is that this would normally require collecting thousands of ants belonging to hundreds of species across the entire Fijian archipelago. Given that only a little over 100 out of 330 islands in Fiji are permanently inhabited, this seemed like an insurmountable challenge.

To go around it, the team figured they could run its tests on ants already collected in Fijian museums. But that came with its own set of difficulties.

DNA pieces

Unfortunately, the quality of DNA that could be obtained from museum collections was really bad. From the perspective of DNA preservation, the ants were obtained and stored in horrific conditions, since the idea was to showcase them for visitors, not run genetic studies. “People were catching them in malaise traps,” Mikheyev says. “A malaise trap is basically a bottle of alcohol that sits somewhere in Fiji for a month. Those samples had horribly fragmented, degraded DNA.”

To work with this degraded genetic material, the team employed a technique they called high-throughput museumomics, a relatively new technique that looks at genetic differences across a genome without sequencing the whole thing. DNA sampled from multiple individuals was cut and marked with unique tags at the same repeated locations, a bit like using bookmarks to pinpoint the same page or passage in different issues of the same book. Then, the team sequenced short DNA fragments following the tag to look for differences between them, allowing them to evaluate the genetic diversity within a population. “We developed a series of methods that actually allowed us to harness these museum-grade specimens for population genetics,” Mikheyev explains.

But the trouble didn’t end there. Differences among Fijian ant taxa are based on their appearance, not genetic analysis. For years, researchers were collecting various ants and determining their species by looking at them. This led to 144 species belonging to 40 genera. For Mikheyev’s team, the first step was to look at the genomes in the samples and see if these species divisions were right. It turned out that they were mostly correct, but some species had to be split, while others were lumped together. At the end, the team confirmed that 127 species were represented among their samples.

Overall, the team analyzed more than 4,000 specimens of ants collected over the past decade or so. And gradually, a turbulent history of Fijian ants started to emerge from the data.

The first colonists

The art of reconstructing the history of entire populations from individual genetic sequences relies on comparing them to each other thoroughly and running a whole lot of computer simulations. “We had multiple individuals per population,” Mikheyev explains. “Let’s say we look at this population and find it has essentially no diversity. It suggests that it very recently descended from a small number of individuals.” When the contrary was true and the diversity was high, the team assumed it indicated the population had been stable for a long time.

With the DNA data in hand, the team simulated how populations of ants would evolve over thousands of years under various conditions, and picked scenarios that best matched the genetic diversity results it obtained from real ants. “We identified multiple instances of colonization—broadscale evolutionary events that gave rise to the Fijian fauna that happened in different timeframes,” Mikheyev says. There was a total of at least 65 colonization events.

The first ants, according to Mikheyev, arrived at Fiji millions of years ago and gave rise to 88 endemic Fijian ant species we have today. These ants most likely evolved from a single ancestor and then diverged from their mainland relatives. Then, a further 23 colonization events introduced ants that were native to a broader Pacific region. These ants, the team found, were a mixture of species that colonized Fiji naturally and ones that were brought by the first human settlers, the Lapita people, who arrived around 3,000 years ago.

The arrival of humans also matched the first declines in endemic Fijian ant species.

Slash and burn

“In retrospect, these declines are not really surprising,” Mikheyev says. The first Fijian human colonists didn’t have the same population density as we have now, but they did practice things like slash-and-burn agriculture, where forests were cut down, left to dry, and burned to make space for farms and fertilize the soil. “And you know, not every ant likes to live in a field, especially the ones that evolved to live in a forest,” Mikheyev adds. But the declines in Fijian endemic ant species really accelerated after the first contact with the Europeans.

The first explorers in the 17th and 18th centuries, like Abel Tasman and James Cook, charted some of the Fijian islands but did not land there. The real apocalypse for Fijian ants began in the 19th century, when European sandalwood traders started visiting the archipelago on a regular basis and ultimately connected it to the global trade networks.

Besides the firearms they often traded for sandalwood with local chiefs, the traders also brought fire ants. “Fire ants are native to Latin America, and it’s a common invasive species extremely well adapted to habitats we create: lawns or clear-cut fields,” Mikheyev says. Over the past couple of centuries, his team saw a massive increase in fire ant populations, combined with accelerating declines in 79 percent of endemic Fijian ant species.

Signs of apocalypse

To Mikheyev, Fiji was just a proving ground to test the methods of working with museum-grade samples. “Now we know this approach works and we can start leveraging collections found in museums around the world—all of them can tell us stories about places where they were collected,” Mikheyev says. His ultimate goal is to look for the signs of the insect apocalypse, or any other apocalypse of a similar kind, worldwide.

But the question is whether what’s happening is really that bad? After all, not all ants seem to be in decline. Perhaps what we see is just a case of a better-adapted species taking over—natural selection happening before our eyes?

“Sure, we can just live with fire ants all along without worrying about the kind of beautiful biodiversity that evolution has created on Fiji,” Mikheyev says. “But I feel like if we just go with that philosophy, we’re really going to be irreparably losing important and interesting parts of our ecology.” If the current trends persist, he argues, we might lose endemic Fijian ants forever. “And this would make our world worse, in many ways,” Mikheyev says.

Science, 2025. DOI: 10.1126/science.ads3004

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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Genetically, Central American mammoths were weird

ancient DNA, Biology, evolution, mammoths, mexico, Science, woolly mammoth / Tim Belzer / August 29, 2025

This led a Mexican-European research collaboration to get interested in finding DNA from elsewhere in the Columbian mammoth’s range, which extended down into Central America. The researchers focused on the Basin of Mexico, which is well south of where any woolly mammoths were likely to be found. While the warmer terrain generally tends to degrade DNA more quickly, the team had a couple of things working in its favor. To begin with, there were a lot of bones. The Basin of Mexico has been heavily built up over the centuries, and a lot of mammoth remains have been discovered, including over 100 individuals during the construction of Mexico City’s international airport.

In addition, the team focused entirely on the mitochondrial genome. In contrast to the two sets of chromosomes in each cell, a typical cell might have hundreds of mitochondria, each of which could have dozens of copies of its genome. So, while the much smaller mitochondria don’t provide as much detail about ancestry, they’re at least likely to survive at high enough levels to provide something to work with.

And indeed they did. Altogether, the researchers obtained 61 new mitochondrial genomes from the mammoths of Mexico from the 83 samples they tested. Of these, 28 were considered high enough quality to perform an analysis.

Off on their own

By building a family tree using this genetic data, along with that from other Columbian and woolly mammoth samples, the researchers could potentially determine how different populations were related. And one thing became very clear almost immediately: They were in a very weird location on that tree.

To begin with, all of them clustered together in a single block, although there were three distinct groupings within that block. But the placement of that block within the larger family tree was notably strange. To begin with, there were woolly mammoths on either side of it, suggesting the lineage was an offshoot of woolly mammoths. That would make sense if all Columbian mammoths clustered together with the Mexican ones. But they don’t. Some Columbian mammoths from much farther north are actually more closely related to woolly mammoths than they are to the Mexican mammoths.

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New dinosaur species is the punk rock version of an ankylosaur

ankylosaurs, Biology, dinosaurs, evolution, paleontology, Science / Rejus Almole / August 28, 2025

And we have known for sure that the armor was around back then, given that we’ve found the skin-derived osteoderms that comprise the armor in Jurassic deposits. But with little more than a rib and a handful of mouth parts to go on, it wasn’t really possible to say much more than that.

Until now, that is. Because the new Spicomellus remains show extremely clearly that the armor of ankylosaurs got less elaborate over time.

The small, solid-looking spikes found along the edges of later ankylosaurs? Forget those. Spicomellus had a back that was probably bristling with sharper spines, along with far larger ones along its outer edges. Each rib appears to have generated as many as six individual spikes. At a handful of locations, these spikes extended out to nearly a meter, looking more like lances than anything needed to ward off a close-in attack.

And the largest of these were along its neck. On the upper surface of its neck, several osteoderms fused to form a massive half-collar of bone and then extended out five or more individual spikes, each among the longest on the animal’s body. And there were three of these structures along the neck. “No known ankylosaur possesses any condition close to the extremely long pairs of spines on the cervical half-ring of Spicomellus,” its discoverers note.

As if its hedgehog-on-acid appearance weren’t enough, handles present on the tail vertebrae suggest that it also had a weaponized tail. All told, the researchers sum things up by saying, “The new specimen reveals extreme dermal armour modifications unlike those of any other vertebrate, extinct or extant, which fall far outside of the range of morphologies shown by other armoured dinosaurs.”

Out go the hypotheses

Because it’s so unusual, the skeleton’s characteristics are difficult to place within a neat family tree of the ankylosaurs. The researchers conclude that some details of its skeleton do suggest Spicomellus groups among the ankylosaurs and conclude that it’s probably an early branch from the main lineage. But without any other significant examples from the lineage at that time, it’s an extremely tentative conclusion. Still, the alternative is that this thing is unrelated to the only other organisms that share at least a few of its bizarre features, which is a difficult idea to swallow.

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Mammals that chose ants and termites as food almost never go back

ants, Biology, diet, evolution, mammals, Science, termintes / Rejus Almole / August 21, 2025

Insects are more influential than we realize

By showing that ant- and termite-based diets evolved repeatedly, the study highlights the overlooked role of social insects in shaping biodiversity. “This work gives us the first real roadmap, and what really stands out is just how powerful a selective force ants and termites have been over the last 50 million years, shaping environments and literally changing the face of entire species,” Barden said.

However, according to the study authors, we still do not have a clear picture of how much of an impact insects have had on the history of life on our planet. Lots of lineages have been reshaped by organisms with outsize biomass—and today, ants and termites have a combined biomass exceeding that of all living wild mammals, giving them a massive evolutionary influence.

However, there’s also a flip side. Eight of the 12 myrmecophagous origins are represented by just a single species, meaning most of these lineages could be vulnerable if their insect food sources decline. As Barden put it, “In some ways, specializing in ants and termites paints a species into a corner. But as long as social insects dominate the world’s biomass, these mammals may have an edge, especially as climate change seems to favor species with massive colonies, like fire ants and other invasive social insects.”

For now, the study authors plan to keep exploring how ants, termites, and other social insects have shaped life over millions of years, not through controlled lab experiments, but by continuing to use nature itself as the ultimate evolutionary archive. “Finding accurate dietary information for obscure mammals can be tedious, but each piece of data adds to our understanding of how these extraordinary diets came to be,” Vida argued.

Evolution, 2025. DOI: 10.1093/evolut/qpaf121 (About DOIs)

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.

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Enigmatic hominin species studied using 2 million-year-old proteins

ancient proteins, Biology, evolution, human evolution, mass spec, paleontology, proteins, Science / Tim Belzer / May 30, 2025

The absence of AMELY suggests that a sample is female, but it isn’t definitive. That’s both because it’s impossible to rule out some problem with identifying the protein in samples this old, and in part because some rare males (including at least one Neanderthal) carry deletions that eliminate the gene entirely.

Another key aspect is that some of the 425 amino acid locations differ between hominin species, and even individual members of Paranthropus. Thus, they can potentially serve as a diagnostic of the relationships between and within species and help address some of the confusion about how many species of Paranthropus there were and their relationship with other hominins. While it’s difficult to say too much with only four samples, the researchers found some suggestive evidence.

For example, they tested whether you might see the sort of amino acid variation found among these samples if they all belonged to the same species. This was done by randomly choosing four human genomes and examining whether they had a similar level of variation. They concluded that it was “plausible” that you’d see this level of variation among any four individuals that were chosen at random, but the population of modern humans is likely to be larger than that of Paranthropus, so the test wasn’t definitive.

Among the 425 different amino acids were 16 that had species-specific variations among hominins. Somewhat surprisingly, Paranthropus robustus is the most closely related species to our own genus, Homo, based on a tree built from these variations. Again, however, they conclude that there simply isn’t enough data available to feel confident in this conclusion.

But that should really be an “isn’t enough data yet.” We heard about this paper from regular Ars reader Enrico Cappellini, who happens to be its senior author and faculty at the University of Copenhagen’s Globe Institute. And a quick look over his faculty profile indicates that developing the techniques used here is his major research focus, so hopefully we’ll be able to expand the data available on extinct hominin species with time. The challenge, as noted in the paper, is that the technique destroys a small part of the sample, and these samples are one-of-a-kind pieces of the collective history of all of humanity.

Science, 2025. DOI: 10.1126/science.adt9539 (About DOIs).

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Carnivorous crocodile-like monsters used to terrorize the Caribbean

Biology, crocodiles, evolution, migration, predators, Science / Paul Patrick / May 17, 2025

How did reptilian things that looked something like crocodiles get to the Caribbean islands from South America millions of years ago? They probably walked.

The existence of any prehistoric apex predators in the islands of the Caribbean used to be doubted. While their absence would have probably made it even more of a paradise for prey animals, fossils unearthed in Cuba, Puerto Rico, and the Dominican Republic have revealed that these islands were crawling with monster crocodyliform species called sebecids, ancient relatives of crocodiles.

While sebecids first emerged during the Cretaceous, this is the first evidence of them lurking outside South America during the Cenozoic epoch, which began 66 million years ago. An international team of researchers has found that these creatures would stalk and hunt in the Caribbean islands millions of years after similar predators went extinct on the South American mainland. Lower sea levels back then could have exposed enough land to walk across.

“Adaptations to a terrestrial lifestyle documented for sebecids and the chronology of West Indian fossils strongly suggest that they reached the islands in the Eocene-Oligocene through transient land connections with South America or island hopping,” researchers said in a study recently published in Proceedings of the Royal Society B.

Origin story

During the late Eocene to early Oligocene periods of the mid-Cenozoic, about 34 million years ago, many terrestrial carnivores already roamed South America. Along with crocodyliform sebecids, these included enormous snakes, terror birds, and metatherians, which were monster marsupials. At this time, the sea levels were low, and the islands of the Eastern Caribbean are thought to have been connected to South America via a land bridge called GAARlandia (Greater Antilles and Aves Ridge). This is not the first land bridge to potentially provide a migration opportunity.

Fragments of a single tooth unearthed in Seven Rivers, Jamaica, in 1999 are the oldest fossil evidence of a ziphodont crocodyliform (a group that includes sebecids) in the Caribbean. It was dated to about 47 million years ago, when Jamaica was connected to an extension of the North American continent known as the Nicaragua Rise. While the tooth from Seven Rivers is thought to have belonged to a ziphodont other than a sebacid, that and other vertebrate fossils found in Jamaica suggest parallels with ecosystems excavated from sites in the American South.

The fossils found in areas like the US South that the ocean would otherwise separate suggest more than just related life forms. It’s possible that the Nicaragua Rise provided a pathway for migration similar to the one sebecids probably used when they arrived in the Caribbean islands.

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Some flies go insomniac to ward off parasites

Biology, circadian rhythm, Drosophila, evolution, fruit flies, parasites, Science / Kris Guyer / May 4, 2025

Those genes associated with metabolism were upregulated, meaning they showed an increase in activity. An observed loss of body fat and protein reserves was evidently a trade-off for resistance to mites. This suggests there was increased lipolysis, or the breakdown of fats, and proteolysis, the breakdown of proteins, in resistant lines of flies.

Parasite paranoia

The depletion of nutrients could make fruit flies less likely to survive even without mites feeding off them, but their tenaciousness when it comes to staying up through the night suggests that being parasitized by mites is still the greater risk. Because mite-resistant flies did not sleep, their oxygen consumption and activity also increased during the night to levels no different from those of control group flies during the day.

Keeping mites away involves moving around so the fly can buzz off if mites crawl too close. Knowing this, Benoit wanted to see what would happen if the resistant flies’ movement was restricted. It was doom. When the flies were restrained, the mite-resistant flies were as susceptible to mites as the controls. Activity alone was important for resisting mites.

Since mites are ectoparasites, or external parasites (as opposed to internal parasites like tapeworms), potential hosts like flies can benefit from hypervigilance. Sleep is typically beneficial to a host invaded by an internal parasite because it increases the immune response. Unfortunately for the flies, sleeping would only make them an easy meal for mites. Keeping both stereoscopic eyes out for an external parasite means there is no time left for sleep.

“The pattern of reduced sleep likely allows the flies to be more responsive during encounters with mites during the night,” the researchers said in their study, which was recently published in Biological Timing and Sleep. “There could be differences in sleep occurring during the day, but these differences may be less important as D. melanogaster sleeps much less during the day.”

Fruit flies aren’t the only creatures with sleep patterns that parasites disrupt. Evidence of shifts in sleep and rest in birds and bats has been shown to happen when there is a risk of parasitism after dark. For the flies, exhaustion has the upside of better fertility if they manage to avoid bites, so a mate must be worth all those sleepless nights.

Biological Timing and Sleep, 2025. DOI: 10.1038/s44323-025-00031-7

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