If an axolotl loses a leg, it gets a new one–complete with a functional foot and all four toes. Over just a few weeks or months, bone, muscle, skin, and nerves grow back in exactly the same formation as the lost limb. The endangered, aquatic, Mexican salamander are masters of regeneration, showcasing the best of an ability shared by many other amphibians, reptiles, and fish species. But how do these cold-blooded creatures do it?

That some species can regrow limbs while others can’t is one of the oldest mysteries in biology, says James Monaghan, a developmental biologist at Northeastern University. Aristotle noted that lizards can regenerate their tails more than 2,400 years ago, in one of the earliest known written observations of the phenomenon. And since the 18th century, a subset of biologists studying regeneration have been working to find a solution to the puzzle, in the hopes it will enable medical treatments that help human bodies behave more like axolotls. It may sound sci-fi, but Monaghan and others in his field firmly believe people might one day be able to grow back full arms and legs post-amputation. After all that time, the scientists are getting closer. 

Monaghan and a team of regeneration researchers have identified a critical molecular pathway that aids in limb mapping during regrowth, ensuring that axolotls’ cells know how to piece themselves together in the same arrangement as before. Using gene-edited, glow-in-the-dark salamanders, the scientists parsed out the important role of a chemical called retinoic acid, a form of vitamin A and also the active ingredient in the acne medicine isotretinoin (commonly known as Accutane). The concentration of retinoic acid along the gradient of a developing replacement limb dictates where an axolotl’s foot, joint, and leg segments go, according to the study published June 10 in the journal Nature Communications. Those concentrations are tightly controlled by just one protein also identified in the new work and, in turn, have a domino effect on a suite of other genes. 

“This is really a question that has been fascinating developmental and regenerative biologists forever: How does the regenerating tissue know and make the blueprint of exactly what’s missing?,” Catherine McCusker, a developmental biologist at the University of Massachusetts Boston who was uninvolved in the new research, tells Popular Science. 

The findings are “exciting,” she says, because they show how even the low levels of retinoic acid naturally present in salamander tissues can have a major impact on limb formation. Previous work has examined the role of the vitamin A-adjacent molecule, but generally at artificially high dosages. The new study proves retinoic acid’s relevance at normal concentrations. And, by identifying how retinoic acid is regulated as well as the subsequent effects of the compound in the molecular cascade, Monaghan and his colleagues have “figured out something that’s pretty far upstream” in the process of limb regeneration, says McCusker. 

Understanding these initial steps is a big part of decoding the rest of the process, she says. Once we know the complete chemical and genetic sequence that triggers regeneration, biomedical applications become more feasible. 

“I really think that we’ll be able to figure out how to regenerate human limbs,” McCusker says. “I think it’s a matter of time.” On the way there, she notes that findings could boost our ability to treat cancer, which can behave in similar ways to regenerating tissues, or enhance wound and burn healing. 

Monaghan and his colleagues started on their path to discovery by first assessing patterns of protein expression and retinoic acid concentration in salamander limbs. They used genetically modified axolotls that express proteins which fluoresce in the presence of the target compounds, so they could easily visualize where those molecules were present in the tissue under microscopes. Then, they used a drug to tamp down naturally occurring retinoic acid levels, and observed the effects on regenerating limbs. Finally, they produced a line of mutant salamanders lacking one of the genes in the chain, to pinpoint what alterations lead to which limb deformities. 

They found that higher concentrations of retinoic acid tell an Axolotl’s body to keep growing leg length, while lower concentrations signal it’s time to sprout a foot, according to the new research. Too much retinoic acid, and a limb can grow back deformed and extra-long, with segments and joints not present in a well-formed leg, hampering an axolotl’s ability to easily move. One protein, in particular, is most important for setting the proper retinoic acid concentration. 

“We discovered it’s essentially a single enzyme called CYP26b1, that regulates the amount of tissue that regenerates,” Monaghan says. CYP26b1 breaks down retinoic acid, so when the gene that makes the protein is activated, retinoic acid concentrations drop, allowing the conditions for foot and digit formations. 

At least three additional genes vital to limb mapping and bone formation seem to be directly controlled by concentrations of retinoic acid. So, when retinoic acid concentrations are off, expression of these genes is also abnormal. Resulting limbs have shortened segments, repeat sections, limited bone development, and other deformations.

Based on their observations, Monaghan posits that retinoic acid could be a tool for “inducing regeneration.” There’s “probably not a silver bullet for regeneration,” he says, but adds that many pieces of the puzzle do seem to be wrapped up in the presence or absence of retinoic acid. “It’s shown promise before in the central nervous system and the spinal cord to induce regeneration. It’s not out of the question to also [use it] to induce regeneration of a limb tissue.” 

Retinoic acid isn’t just produced inside axolotls. It’s a common biological compound made across animal species that plays many roles in the body. In human embryo development, retinoic acid pathways are what help map our bodily orientation, prompting a head to grow atop our shoulders instead of a tail. That’s a big part of why isotretinoin can cause major birth defects if taken during pregnancy–because all that extra retinoic acid disrupts the normal developmental blueprint. 

Yet retinoic acid isn’t the only notable factor shared by humans and amphibians alike. In fact, most of the genes identified as part of the axolotl limb regrowth process are also present in our own DNA. What’s different seems to be how easily accessed those genetic mechanisms are after maturity. Axolotls, says Monaghan, have an uncanny ability to activate these developmental genes as needed. 

Much more research is needed to understand exactly how and why that is, and to get to the very root of regeneration ability, but the implication is that inducing human limbs to regrow could be easier than it sounds. 

“We might not need to turn on thousands of genes or turn off thousands of genes or knock out genes. It might just be triggering the reprogramming of a cell into the proper state where it thinks it’s an embryo,” he says.

And lots of research is already underway. Other scientists, McCusker included, have also made big recent strides in attempting to unlock limb regeneration. Her lab published a study in April finding key mechanisms in the lateral mapping of limbs–how the top and bottom of a leg differentiate and grow. Another major study from scientists in Austria came out last month pinpointed genetic feedback loops involved in positional memory, which help axolotl tissues keep tabs on where lost limbs once were and how they should be structured. 

Still, it’s likely to be decades more before human amputees can regain their limbs. Right now, the major findings fall in the realm of foundational science, says McCusker. Getting to the eventual goal of boosting human regenerative abilities will continue to take “a huge investment and bit of trust.” But every medical treatment we have today was similarly built off of those fundamental building blocks, she says. 

“We need to remember to continue to invest in these basic biology studies.” Otherwise, the vision of a more resilient future, where peoples’ extremities can come back from severe injury, will remain out of reach.

The post A chemical in acne medicine can help regenerate limbs appeared first on Popular Science.

If you own an iPhone, you’re never far away from a major or minor software update. So while iOS 18.4 doesn’t introduce as many features as the main iOS 18 release, it does come with a few interesting new tricks.

Specifically, there’s now the option to open your favorite chat in Messages, right from the lock screen. It might be the group chat with your friends, for example, or the one-to-one conversation you’ve got going with your partner. If there’s a special conversation that stands out, you can now get at it more quickly.

It’s not difficult to set up via the Shortcuts app—and it adds to the other shortcuts and customizations you can make. In fact, any shortcut you can imagine can be put on the iOS lock screen for easy access, though currently there’s only room for two at a time.

This new iOS 18.4 feature works through the Shortcuts app, so head there first. Tap + (plus) in the top right corner, then search for the “open conversation” shortcut in the text box. When the link appears, tap to select it.

You then need to choose the conversation to open: Tap on the blue Conversation field to do this, then pick a chat from the Messages app. A list of all the contacts you’ve been chatting with recently shows up, so make your pick—you can choose SMS and RCS conversations, as well as those handled by iMessage.

You can then tap Done to save the shortcut on your iPhone. If you like, you can configure several shortcuts to several chats, and switch between them as needed—not just from the lock screen, but from wherever shortcuts appear (like the Control Center, for example).

With our shortcut(s) created, we can head to the lock screen and make use of the latest customization options there. With your phone locked, tap and hold on the display, then choose Customize and Lock Screen.

You’ll see two shortcuts down in the lower left and right corner—usually the flashlight and the camera, if you’ve left the defaults in place. Tap the – (minus) button to clear either the right or the left shortcut, then tap the + (plus) button that’s revealed.

Pick Shortcuts, then tap Choose to select one, and then tap the Open Conversation shortcut you just created. No more configuration is required, and you simply need to tap Done to confirm. In the future, long press on this shortcut, and your chosen chat appears (after you’ve gone through lock screen security).

It’s easy to see how the same approach can be used to set up other shortcuts. iOS 18.4 has only just added the ability to link to a specific conversation inside Messages, but there’s lots more that you can do with these links from the lock screen.

For example, you can set up a link to send a message to a particular recipient—both in Messages and third-party tools such as WhatsApp. If there’s someone you find yourself messaging a lot, it can save you some time.

You can also pick a Set Messages Focus Filter shortcut, which will instantly apply one of the focus modes on your iPhone to message notifications. The benefit of having them on the lock screen is you don’t need to dig through a variety of menus to find them.

Messaging apps know full well that some of your conversations are more important than others—it would be a little strange if they weren’t—and most of the popular mobile messaging apps give you tools for prioritizing certain chats, on top of the links you can place on the lock screen.

In Apple Messages, for example, long press on a message and choose Pin to keep it at the top of the chat list. There’s a similar feature in WhatsApp, only in this case you need to swipe right on a message in the chat list to find the Pin option.

And don’t forget Siri either: With a “hey Siri” voice command or a long press on the power button, you can invoke the digital assistant and get it to send a message to a contact, in a choice of apps—even from the lock screen.

The post New iPhone trick puts your favorite chat on the lock screen appeared first on Popular Science.

The FDA has greenlit the first lab-grown fish for public consumption, and it’s already available in a restaurant. The dish’s developers at the startup Wildtype confirmed the regulatory milestone last week, but for now, hungry and curious taste-testers will need to head to Portland, Oregon, to sample the company’s “cultivated salmon.”

“We’re proud to share that we completed a thorough pre-market safety consultation with [the] FDA,” Wildtype said in its announcement along with a link to the agency’s response letter.

FDA’s Director Office of Food Chemical Safety, Dietary Supplements, and Innovation Human Foods Program confirmed the agency has “no questions at this time” about Wildtype’s “cultured salmon cell material,” and described it “as safe as comparable foods produced by other methods.”

As The Verge notes, such consultations are entirely voluntary for companies, but can still serve as a means to boost consumer confidence and help legitimize a product.

Wildtype’s salmon is not the first lab-grown food to receive the FDA’s stamp of approval—that honor went to two companies’ cultured chicken in 2022—but this does mark the first time a lab-grown fish has earned the distinction. What makes Wildtype’s project particularly distinctive is its choice of salmon cut. Unlike lab-grown chicken or beef, the company is creating sushi-grade “saku” cuts that are intended to be eaten raw. These uniformly cut blocks of fish are most often served as sashimi, and do not require any cook time.

To achieve this, Wildtype’s researchers first harvest living cells from Pacific salmon before transporting them for cultivation. In specially designed equipment, these cells are then grown in cultures with conditions similar to those in the wild fish itself. These include fine-tuned pH levels, temperatures, nutrients, and other factors that induce the cells to develop to a point when engineers can harvest them. From there, the team integrates “a few plant-based ingredients” to help hone the flavor, texture, and appearance of wild salmon filets.

Wildtype’s cultivated salmon debuted in late May at Kann, a James Beard Award-winning Haitian restaurant located in Portland, Oregon. Overseen by chef Gregoary Goudet, the saku cuts are currently paired with spiced tomato, pickled strawberry, strawberry juice, and a rice cracker topped with epis, a pesto-like traditional Haitian blend of garlic, peppers, and herbs. Kann will begin including the salmon on its daily menu in July, while Wildtype says another four restaurants plan to integrate the fish into their own dishes in the coming months.

The next restaurants have yet to be named, but they likely won’t be located in one of the eight states that have already instituted bans on serving lab-grown meat. These prohibitions aren’t based on any particularly well-founded concerns, however. Critics frequently cite a threat to the farming industry, but given the comparative costs, lab-grown meat isn’t likely to supplant traditional options anytime soon.

The post FDA approves lab-grown salmon appeared first on Popular Science.

My thoughts often feel like endless streams of information. That’s until someone asks me the name of a stranger I met six or seven seconds before, and my mind goes blank. Mind blanking is much more common than you might think. Researchers think that our minds are blank somewhere between 5 and 20 percent of the time. Neuroscientists face significant hurdles in adding color and detail to the mystery of an empty mind, but new research is trying to establish the edges of these formless thoughts. 

Athena Demertzi, a cognitive neuroscientist at the University of Liège, recently published a review paper on mind-blanking research. The field has struggled to agree on what the term means–Demertzi’s paper lists no fewer than seven different definitions. Her preferred view is that mind blanking is about “the impression of having no thoughts or not being able to report any thoughts.” 

This interpretation is intentionally vague, as people can use all kinds of language to self-report a mind blank. Examples include “I don’t remember what I was thinking” or “I wasn’t paying attention.” Demertzi says that this can trip up researchers who attempt to incorporate other brain processes, such as memory, into their work.

Within this broad definition, Demertzi then works to separate different strands of mind blanking. This work is fraught with complications. One of the most reliable tools for examining the brain’s inner workings is functional magnetic resonance imaging (fMRI). Demertzi explains that fMRI researchers often ask their volunteers to “think of nothing” while in the scanner. Doing so causes activation along the midline of the brain in regions like the cingulate cortex, says Demertzi. However, rather than being a marker of a blank mind, this signal is a cognitive marker of the effort required to suppress thoughts. 

To block out this signal, Demertzi tried a different strategy. In a 2023 study, her team monitored the brains of people at rest in a scanner. At random intervals, participants were asked to report what they had been thinking of. The team then analyzed the brain activity patterns in the seconds preceding their response. The brains of individuals who reported blank minds showed a distinct signal, a pattern involving a momentary synchronization of brain networks. “They are all deactivated,” says Demertzi. This signal is also seen during sleep or anesthesia, she adds. 

This finding is supported by other research that has established a strong link between mind blanking and the level of stimulation our brains are experiencing, called arousal. When arousal levels are low, mind-blanking episodes are more likely to occur. This is suggested to be because high arousal is necessary to keep up a continuous stream of thought. 

There may be a cost to keeping up a very high state of arousal, however. At high levels, this focus tips over into anxiety, which inhibits performance. Demertzi’s paper points out that these anxious states can lead to racing thoughts that may blur individual ideas and make them hard to recall–another form of mind blanking. 

In certain cases, mind blanking can even be a feature of clinical conditions. “We know that it manifests in clinical states like ADHD,” says Demertzi. Unmedicated kids with ADHD report mind blanking at a higher rate than kids without the condition. Other conditions that feature racing thoughts, like generalized anxiety disorder, also include mind blanking as a related feature.

The ultimate question for Demertzi is why mind blanking happens in the first place. Researchers are still trying to figure this out, although she suggests that the link to sleep and arousal may be a hint. “When we sleep,” says Demertzi, “Our neurons are getting rest by throwing away what has been accumulated throughout the day through the glymphatic system.” 
Demertzi says that this toxin-clearing function–which is disputed by some sleep neuroscientists–may also occur in brief periods while we are awake. We notice these “pit stops” in cognition as mind blanks. Ultimately, these blanks may be a way our brain maintains high function for the rest of our waking experience. “How can you sustain a continuous wakeful life if our brains are not helping a bit?” says Demertzi.

The post What happens when our brain goes blank appeared first on Popular Science.

Affordable housing is hard to build not because of lack of need, but because of how it's financed. This guide explains the basics, including:

• Capital Stack: Projects are funded through a mix of debt and equity, used to cover land, construction, and soft costs.
• The Funding Gap: Affordable rents generate less income, meaning smaller loans—creating a gap that must be filled to make a project viable.
• Closing the Gap: Developers use a mix of:
  • Subsidies (grants, tax credits, vouchers)
  • Cost-saving strategies (donated land, fee waivers)
  • Lower-cost capital (below-market loans and equity)
• Why It Matters: Understanding these tools helps advocates, policymakers, and funders support more sustainable, equitable housing development.

• Affordable Housing
• Housing Development
• Housing Costs
• Housing Supply

This year’s swag at the Early Check in at Infinite Loop #WWDC25 #WWDC2 pic.twitter.com/yBo1CxuYwB

As a dad who’s spent more time than I’d like to admit wrestling an iPad away from my toddler, I’ve seen the dark side of kids’ screen time. Those hyperactive, ad-riddled apps turn my kid into a tiny, overstimulated zombie. So when I stumbled upon this Pok Pok: Lifetime Subscription—a Montessori-inspired app designed for kids aged 2 to 8—I was intrigued.

Pok Pok isn’t your typical kids’ app. There are no levels, no timers, and no “You Win!” screens. Instead, it offers open-ended play that encourages curiosity and exploration. Think of it as a digital sandbox where kids can tinker with shapes, explore space, or go on number journeys—all without the pressure to achieve a high score.

For parents looking to introduce their kids to screen time in a healthy, guilt-free way, Pok Pok is a game-changer. It was designed by early childhood experts to be enriching and supportive of children’s development. What sets Pok Pok apart is its commitment to low-stimulation interactivity. The hand-drawn animations and gentle sound design create a calming experience that doesn’t overwhelm young minds. Plus, it works offline on iPhone, iPad, and Android, making it a lifesaver during long car rides or flights. And with no in-app purchases or hidden fees, I don’t have to worry about surprise charges.

From a developmental standpoint, Pok Pok aligns with Montessori principles, focusing on hands-on learning and independence through play. It supports cognitive, social, and emotional development, helping kids build foundational skills in STEM, problem-solving, and language. And with regular updates, there’s always something new to explore.

Right now, a lifetime subscription to Pok Pok is $49.99, with the code SAVE10 at checkout. That’s a one-time purchase for endless educational play.

Sale ends July 20 at 11:59 p.m. PT

StackSocial prices subject to change.

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Pok Pok: Lifetime Subscription

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The post Give your little explorer screen time that fuels creativity appeared first on Popular Science.

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The San Francisco Unified School District opened its first affordable housing development, Shirley Chisholm Village, “a 135-unit housing complex in San Francisco’s oceanside Sunset District. Built on district-owned land, with affordable rents and preference given to SFUSD educators.”

As Nate Berg explains in Fast Company, “The $105 million project was developed by the nonprofit MidPen Housing with a design by San Francisco-based BAR Architects & Interiors in association with G7A | Gonzales Architects, and in coordination with the San Francisco Mayor’s Office of Housing and Community Development.”

The units are reserved for residents who make between 30 and 100 percent of the area median income and represent a growing movement by school districts to use their resources to provide workforce housing for educators and district employees. The district has three additional housing projects in the works.

The building includes a fifth floor work-from-home area and gathering space separate from the private living spaces. “Though the project was not required to include parking under the city’s zoning code, the developers chose to include some underground spaces, partly to assuage neighborhood concerns about street parking and partly at the request of the educators who helped guide the design process.”

Prior to the housing development, the lot was vacant, with the community using it as a park. To address the loss of this communal space, the development includes a public plaza, playground, and seating area accessible from the street.

• San Francisco
• Workforce Housing
• Affordable Housing
• housing affordability
• Housing Costs

A sprawling suburb 40 miles east of Los Angeles is about to become a major passenger rail hub once Brightline West, a high-speed rail line connecting Las Vegas and Southern California, is complete.

As Sarah Stodola explains in Bloomberg CityLab, Rancho Cucamonga will be the western terminus of Brightline West, where travelers will be able to connect to other Southern California rail lines.

With the state’s more notorious north-south high-speed rail project languishing, Brightline West will likely become the state’s first operational high-speed rail line. “The city believes it can leverage its new high-speed rail station — and the millions of riders that will potentially pass through it — to build the kind of transit-oriented urban core that towns in postwar Southern California have historically struggled to cultivate.”

City leaders are preparing for a shift to more multimodal, pedestrian-friendly development by revamping its zoning codes to support active building frontages and walkable, mixed-use blocks. It now prohibits parking in the front of buildings and has eliminated parking requirements near transit stations. A new development already in progress near the existing Metrolink station will redevelop a defunct golf course into a mixed-use development with over 3,000 housing units, increasing density near the train hubs.

• Rancho Cucamonga
• Brightline West
• High-Speed Rail
• Walkability
• Transit-Oriented Development
• Passenger Rail

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A proposed bitcoin mine in Alaska would use natural has to produce as much energy as is produced by the state’s largest coal plant, reports Nathaniel Herz in the Alaska Beacon.

The startup planning the project, Stax Capital Partners, “recently applied for a permit with state land managers to set up shipping container-like pods housing natural gas generators and computers at a site some 30 miles south of the massive Prudhoe Bay oil field. The generators would be fueled by the basin’s huge stores of ‘stranded’ natural gas — an industry term for gas that doesn’t have a pipeline connecting it to potential customers.”

Alaska officials have been positioning the state as ideal for Bitcoin operations, which require massive amounts of energy. “But developing new industries in the region is challenging due to its remote location and steep construction costs. And oil companies on the North Slope haven’t ever sold large quantities of gas for Alaska-based data centers or Bitcoin mining, so it’s not yet known whether their asking price would be low enough to offset the higher costs of building and operating infrastructure in the Arctic.”

Phil Wight, an energy historian at the University of Alaska Fairbanks, warns that the project could add to the industrialization of the fragile region and increase carbon emissions.

• Bitcoin
• Cryptocurrency
• Energy Use
• Natural Gas

I knew city light pollution clouded the stars, but when I went camping in the country for the first time, seeing the Milky Way nearly knocked me over. I’d been hearing about the real night sky since I was a kid, but seeing it was something else.

I wanted to stare for hours, take in the sweeping collections of stars, pick out the Dippers, and while the neck strain got to me late in the night, my eyes were comfortable, and the stars were in focus with the Double Barrel 720p Digital Night-Vision Binoculars. The best part is that they’re on sale for $119.99 (regular price $297.99).

These binoculars can do it all: snap photos, record video, and play it back. With the included 32 GB TF card, you can keep everything you capture. I loved how the infrared LEDs let me see in total darkness or dimly lit spots, and the TFT widescreen display made it super easy to dial in focus and tweak the lighting.

When I got home, seeing the videos on my computer screen—and my friends and family don’t know this—made me tear up. They looked like stock pictures that I hadn’t really comprehended were based on the sky I sleep under every night.

Murky city air’s got nothing on those wide-open rural skies; I’m going camping every summer. With the 4x zoom, I’m not missing anything ever again. Living in the city is great, but now that I know what else is out there, I’m kind of obsessed.

If you want to change how you see the sky and the world around you, it’s time for night-vision binoculars.

Get the Double Barrel 720p Digital Night-Vision Binoculars for $119.99 (reg. $297.99).

StackSocial prices subject to change.

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Double Barrel 720p Digital Night-Vision Binoculars

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The post A smog‑free sky had me reaching for these binoculars appeared first on Popular Science.