27 April 2026

Today’s Deep Dive delves into three-legged movement. But first, catch up on the latest science news, including the Amazon’s cloudy future and ancient humans’ dislike of mosquitoes.

Cancer | Science

Why cancer rarely takes heart

Primary cardiac tumors—cancers that develop in the heart—are exceptionally rare. New research in Science suggests that this low incidence may be because the heart beats: The continuous mechanical stress seems to stymie cancer growth.

In one experiment, researchers introduced potent cancer-driving mutations into mice that often develop tumors. Cancers occurred elsewhere in the body, but not in the heart. The team next created a side-by-side comparison within the same animal by observing a native heart still pumping under normal strain, and a donor heart kept alive with blood flow but without having to do the mechanical work of pumping. Tumors grew preferentially in the lower-strain heart.

Researchers saw the same effect after injecting several types of human cancer cells directly into heart tissue: In beating hearts, many remained as only small clusters, while in less-strained hearts, they grew larger. Further analyses showed that cancer cells in beating hearts had weirdly shaped nuclei, condensed chromatin, more tightly packed DNA, and lower activity in genes tied to growth and cell division.

The team also rhythmically stretched cancer cells in the lab and concluded that strain alone could reproduce some of these antigrowth features. The study’s co-lead author, Giulio Ciucci, told Science Podcast Host Sarah Crespi that the team is already testing prototype devices designed to rhythmically compress superficial tumors, in the hopes of recreating the heart’s protective mechanism. And as Wyatt Paltzer and James Martin point out in a related Perspective, it may be possible to recreate the effect of mechanical strain pharmacologically, providing new avenues for cancer treatments.

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Climate | Science

A cloudy future for the Amazon

Deforestation practices such as logging can increase cloud cover, which reduces warming by reflecting sunlight. RICH CAREY/GETTY IMAGES.

Deforestation in the Amazon isn’t just disruptive for local plants and animals; it’s also disruptive for the planet at large. Burning plant matter adds carbon to the atmosphere directly, but there are also indirect changes—to the amount of sunlight reflected back to space, the composition of the atmosphere, and even the formation of clouds—any of which can mediate or stoke global warming.

To begin to understand the broader impacts of deforestation, researchers analyzed 2 decades of satellite observations to compare cloud cover over areas that had and had not been deforested. They found a clear trend: Cloud cover increases with more deforestation, with the most cleared areas seeing 5% more cloud cover. Clouds were also lower in deforested areas compared to intact ones—a positive note for the climate, since low clouds reflect more of the sun’s radiation than they trap.

However, the study shouldn’t be seen as a hall pass for continued forest loss, not least because the atmospheric effects of aerosols from burning are unclear. “Notably, there is no indication that the net biophysical effect of Amazon deforestation will completely offset the warming, even with the cloud changes,” explained atmospheric scientist Gunnar Myhre in a related Perspective. “It is important to maintain and restore Amazon forest cover for mitigating climate change and sustaining critical ecosystems.”

read the Science Paper

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Anthropology | Science Advances

Ancient humans hated mosquitoes even more than we do now

When choosing where to live, early humans needed to be around natural resources—places with plenty of opportunities for foraging and agriculture—and were therefore heavily influenced by temperature, rainfall, and shifting landscapes. Those same conditions also affect how infectious diseases spread, which could also impact settlement. A new study published in Science Advances suggests that malaria—one of humanity’s oldest and most persistent pathogens—likely shaped where human populations lived across Africa tens of thousands of years ago.

To estimate malaria risk for people living from 74,000 to 5000 years ago, the team modeled the probable past distribution of malaria-carrying mosquitoes using environmental and climate data, then combined this with epidemiological factors to calculate a “malaria stability index”: a measure of how likely transmission would have been in a given place at a given time. They then compared those maps to reconstructions of where humans lived, which were based on archaeological sites across sub-Saharan Africa.

In the distant past, the two patterns rarely overlapped. But that relationship began to change around 15,000 to 10,000 years ago: Over time, human populations coincided more with high-risk regions, particularly in West Africa. The shift aligns chronologically with genetic evidence for the spread of malaria-resistant traits such as the sickle cell mutation, suggesting that humans had started to adapt to a disease they had previously avoided.

“Disease has rarely been considered a major factor shaping the earliest prehistory of our species, and without ancient DNA from these periods it has been difficult to test” explained geoanthropologist and senior author Eleanor Scerri. “Our research changes that narrative and provides a new framework for exploring the role of disease in deep human history.”

Read the paper

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Deep Dive

One less leg makes walking trickier for pups—but running is largely unaffected. Davies et al./Proceedings of the Royal Society B (2026)

Three-legged dogs strut their stuff

Phie Jacobs, General Assignment Reporter, News from Science

What walks on four legs in the morning, two legs in the afternoon, and three legs in the evening? If you’re familiar with Greek mythology, you probably already know the answer to this riddle. According to some scientific perspectives, however, the solution is a bit more complicated.

When describing how animals move around, scientists often speak in terms of “gait,” which can refer to different styles or speeds of locomotion. A person might walk with a stiff or crouching gait, for example, while a horse may walk, trot, canter, or gallop. Interestingly, while horses employ a transverse gallop, in which landing and takeoff occur on opposite sides of the body, cheetahs use a faster rotary gallop.

Researchers have extensively characterized the gaits of animals that go about on two or four legs, but they understand comparatively little about locomotion on three legs, which rarely happens in nature. A gorilla, for example, might occasionally use one arm to carry something while supporting its weight with the other, while a spider monkey can use its tail as a third “limb” while swinging between trees. True tripedalism, however, really only occurs in four-legged animals—such as dogs—that have lost a limb.

Do these animals have discrete, identifiable gaits? According to Zoe Davies, a biomechanist and veterinary physiotherapist at the Royal Veterinary College in the United Kingdom, the term has no “proper, dictionary-level definition.” Some scientists have described a gait as a regularly repeating cycle of movement, but this definition automatically excludes irregular gaits that may occur due to an injury or disability. “If you’re walking with a limp,” Davies reasons, “you’re still walking.”

In a study published last week in Proceedings of the Royal Society B, Davies and her colleagues recorded and analyzed the movement patterns of 12 different three-legged dogs, including six forelimb and six hindlimb amputees . Each dog was covered with retroreflective markers, allowing the researchers to track their motion in three dimensions, while force plates measured the pressure exerted by each paw. Some of the participating pups needed a little bit of extra encouragement to move normally. “Not all dogs love having stickers all over them, especially their feet,” Davies explains. Treats, toys, and attention went a long way in helping them feel more comfortable. “I did all of the cuddling and all of the playing.”

The work revealed that, at high speeds, three-legged dogs employ a fluid, gallop-like gait. “If you see them running super fast, you take a while to even recognize that they’re missing a limb,” says Davies. “They move really smoothly.” At low speeds, however, the gaits become more awkward, switching between a slowed-down version of the gallop and an irregular, lurching walk. “They’re almost undecided on what to do,” Davies explains. “There’s a lot of pitching of the body, a lot of bouncing.”

The researchers also noted some differences between forelimb and hindlimb amputees. Dogs missing one of their front legs, for example, tended to put more weight on the remaining front limb, while those missing a hind leg distributed force more evenly across all three remaining limbs. When galloping, forelimb amputees used a rotary-like sequence, while hindleg amputees used a combination of rotary and transverse patterns.

As a veterinary physiotherapist, Davies is particularly interested in how these findings can inform recovery plans for animals that have lost a limb. Veterinarians typically err on the side of caution by having dogs move around slowly and carefully after surgery, which might not actually be the most comfortable. “How do we rehabilitate these animals to move normally if we don’t know what normal is?”

The work may also have applications beyond veterinary medicine. As Davies notes, scientists have made great strides in the field of four-legged robots, and these researchers may be interested in designs that can still function when one of those limbs is damaged or lost. “Having a bit of a knowledge of how stuff works on three legs is useful,” she says. Scientists across fields can probably agree, she adds, that three-legged dogs are “particularly cute.”

Read the paper

Et Cetera

Under review

A controversial decision by the Trump administration to pull a vaccine study from the Morbidity and Mortality Weekly Report—which, for 65 years, has been a mainstay for conveying urgent public health data—stirred up controversy last week and could portend an overhaul of the venerable publication. One global health lawyer called the move “political interference in science.”