Science

by Issam AHMED

First came the slow hand movements, then the tremor, and now the looming fear of what lies ahead.

Scientists analyzing 2,000-year-old DNA have revealed that a Celtic society in the southern UK during the Iron Age was centered around women, backing up accounts from Roman historians, a study said Wednesday.

When historians such as Tacitus and Cassius wrote about Rome conquering Britain from around AD 44 to 84, they described women holding positions of power.

Outgoing U.S. President Joe Biden's administration on Wednesday announced a ban on Red Dye No 3, a controversial food and drug coloring long known to cause cancer in animals.

Decades after scientific evidence first raised alarm, Red 3, as it is also called, is currently used in nearly 3,000 food products in the United States, according to the nonprofit Environmental Working Group.

Sergio Flores with Issam Ahmed in Washington

Elon Musk's SpaceX is gearing up for the seventh orbital flight test of Starship, the colossal prototype rocket the company hopes will help humans colonize Mars.

by Julien Dury and Daniel Lawler

Do people with obesity have an illness? A panel of global health experts looking at this controversial question announced Wednesday that the definition of obesity should be split into two categories -- and diagnosed using more accurate measurements.

From self-service checkouts to public streets to stadiums – surveillance technology is everywhere.

This pervasive monitoring is often justified in the name of safety and security.

News stories about the likely existence of extraterrestrial life, and our chances of detecting it, tend to be positive. We are often told that we might discover it any time now. Finding life beyond Earth is “only a matter of time”, we were told in September 2023. “We are close” was a headline from September 2024.

It’s easy to see why. Headlines such as “We’re probably not close” or “Nobody knows” aren’t very clickable. But what does the relevant community of experts actually think when considered as a whole? Are optimistic predictions common or rare? Is there even a consensus? In our new paper, published in Nature Astronomy, we’ve found out.

The Bible’s lex talionis – “Eye for eye, tooth for tooth, hand for hand, foot for foot” (Exodus 21:24-27) – has captured the human imagination for millennia. This idea of fairness has been a model for ensuring justice when bodily harm is inflicted.

Thanks to the work of linguists, historians, archaeologists and anthropologists, researchers know a lot about how different body parts are appraised in societies both small and large, from ancient times to the present day.

With a president-elect who has called the climate crisis a "hoax" and vowed to gut fossil fuel drilling regulations poised to take office in one week, more than 50,000 scientists and advocates on Monday implored U.S. lawmakers to consider the incoming administration's "respect for science" as they vote on Cabinet nominees and provide oversight of the Trump White House over the next four years.

Organized by the Union of Concerned Scientists (UCS), a petition signed by 50,588 scientists and experts was sent to every member of Congress, asking them to "defend the science and scientists that keep Americans safe" after President-elect Donald Trump takes office on January 20.

Climate campaigners and scientists on Monday welcomed the U.S. Supreme Court's decision to reject attempts by fossil fuel giants to quash the Hawaii capital's lawsuit aiming to hold the major polluters accountable for the devastating impacts of their products.

"This is a significant day for the people of Honolulu and the rule of law," Ben Sullivan, executive director and chief resilience officer at the City and County of Honolulu's Office of Climate Change, Sustainability, and Resiliency, said in a statement.

Saber teeth – the long, sharp, blade-like canines found in extinct predators such as Smilodon – represent one of the most extreme dental adaptations in nature. They evolved at least five times throughout mammalian history and are a classic example of convergence, which is when similar structures evolve independently in unrelated animal groups.

With no living representatives, scientists have long debated how these predators used their fearsome teeth, and why this extreme tooth shape evolved so often.

Our new study, published today in Current Biology, provides an answer. We found extreme sabre teeth are functionally optimal, meaning their shape provided a real advantage as specialized weapons. Their slender and sharp forms were perfect for puncturing prey. However, this came at a cost: sabre teeth were also weaker and more prone to breaking.

These findings are important because they help us better understand how extreme adaptations evolve across nature. They also offer insights into optimal design principles that extend beyond biology into engineering and technology.

Saber-toothed predators through time

Saber-toothed predators once roamed ecosystems around the globe. Their fossils have been found in North America, Europe, Africa and Asia.

The feature that defines them are their sabres, a distinct type of canine tooth. These teeth are long, sharp, laterally compressed (flattened from the sides) and curved.

This is different to the short, robust, conical canines of modern big cats such as lions and tigers.

Many extinct predators around the world evolved saber teeth which are very different to the teeth of modern big cats. Tahlia Pollock

This iconic tooth is older than the dinosaurs. It first appeared around 265 million years ago in a group of mammal-like reptiles called the gorgonopsids.

Over millions of years, saber teeth evolved repeatedly in different groups of carnivorous mammals, marsupial relatives like Thylacosmilus and “false” saber-tooth cats such as Barborofelis.

The most well known saber-toothed predator is Smilodon. It persisted until just 10,000 years ago.

You can look at a 3D model of one of these predators – Smilodon fatalis – below. This model has been digitised from a cast specimen from the Natural History Museum of Los Angeles County.

Based on extensive research into saber-tooth ecology there is a general consensus that these predators primarily targeted large prey, delivering slashing bites to the soft tissue of the throat powered by strong neck muscles. It is thought that their teeth offered an advantage doing this, helping them to deliver the killing bite.

This idea is what we set out to investigate.

Testing the puncture-strength trade-off

Specifically, we tested whether their shape was an optimal balance between two competing needs related to tooth function. First, being sharp and slender enough to puncture prey effectively. Second, being strong and robust enough to resist breaking.

To investigate this, we conducted a large-scale analysis of more than 200 different carnivore teeth, including both extinct sabre-toothed species and modern animals.

First, we measured their 3D shape to show how saber teeth compared to other carnivores. Then we tested how a subset of these teeth performed during biting via two experiments.

We 3D printed tooth models in stainless steel and drove them into a gelatin block (simulating prey flesh) to measure how much force was needed to puncture. We used metal replicas to prevent tooth bending during the experiment, ensuring accurate puncture force measurements.

We also ran engineering simulations to test how much stress different tooth shapes experienced under biting forces. This revealed their likelihood of breaking.

Finally, we conducted an “optimality” test to determine which tooth shapes struck the best balance between puncture efficiency and strength .

A 3D-printed saber tooth being driven into a gelatine block to measure the force needed to puncture.

Extreme saber-tooth forms are optimal

It terms of saber-tooth shape, our results challenge the traditional idea that these predators fell into just two categories: dirk-toothed, which are long and slender, and scimitar-toothed, which are short and laterally compressed.

Instead, we uncovered a continuum of saber-tooth shapes. This ranged from extreme forms, such as the long, curved canines of Barbourofelis, Smilodon and Hopolophoneus, to less extreme forms, such as the straighter, more robust teeth of Dinofelis and Nimravus.

Our results reveal that the extreme saber-toothed forms, like Smilodon, were optimised for puncturing prey with minimal force. However, they were more prone to breakage under high stress.

Less extreme saber-toothed forms, such as Dinofelis, were also optimal but in a different way. They struck a more balanced trade-off between puncture efficiency and strength.

The fact that different saber-toothed species evolved varying balances between puncture efficiency and strength suggests a broader range of hunting strategies than previously thought. This supports a growing body of research on their ecological diversity.

Morphospace’ (visualization of shape diversity) of sabre and non-saber-tooth canines showing areas of optimal performance. Miranta Kouvari & Melisa Morales/Science Graphic Design

A striking solution

These results help explain why extreme sabre teeth evolved so many times, likely driven by natural selection for an optimal design. They also provide a possible explanation for their eventual demise.

Their increasing specialization may have acted as an “evolutionary ratchet”, making them highly effective hunters, but also more vulnerable to extinction when ecosystems changed, and their prey became scarce.

Our study also provides broader insights into how extreme adaptations evolve in other species. By integrating biomechanics with evolutionary theory, we can better understand how natural selection shapes organisms to perform specialized tasks.

The sabre tooth form represents a striking solution to a fundamental mechanical challenge, balancing efficiency with strength — one that is also reflected in human-made tools.

This trade-off between sharpness and durability is a key consideration in engineering, influencing the design of everything from surgical scalpels to industrial cutting blades.

Engineers developing precision tools, such as hypodermic needles or high-performance cutting instruments, can look to nature’s evolutionary solutions for inspiration, applying the same principles that shaped these prehistoric predators.