Fall has arrived in the Northern Hemisphere. The autumn equinox on September 22—one of the two times a year (the other is the spring or vernal equinox) where day and night are the same length—ushers in a explosion of fall colors across the United States, making it one of the best time of year to visit the national parks. Summer’s crowds fall by nearly half, wildlife springs into a final frenzy of activity before winter, and verdant foliage transforms into a stunning riot of color for a few brief but brilliant weeks. The Smoky Mountains’ annual Fall Foliage Prediction Map notes that much of the U.S. will start seeing the most dramatic changes in colors by late September to mid-October. However, the U.S. is coming off its third-hottest summer on record, according to the National Oceanic and Atmospheric Administration. Factors such as extreme weather, precipitation or the lack of it, and insect infestations could cause fall foliage to fall behind schedule—continuing a long-term trend that, according to one recent study of maples by researchers at George Mason University, has pushed the appearance of fall colors back more than a month since the 19th century, Nat Geo’s Sarah Gibbens reports. Still, while the timing can shift from year to year, there is one thing travelers can be sure will not change: Trees will shed their leaves, but not before a grand finale of radiant color. From Virginia’s Skyline Drive to Alaska’s roadless wilderness, explore the national parks that offer one of nature’s most stunning displays.

After the Spanish conquest of Yucatán in the 16th century, the Maya were left at the bottom of a racial caste system imposed by the European colonizers. The Maya language came second to Spanish, while Maya temples were knocked down and the stones used to build Christian churches.

Developed with Maya locals, the trail tells the story of Mexico’s Indigenous peoples and aims to lift the 14 communities that live along its 68-mile route from a history of colonial exploitation and cultural erosion.A three-day bike ride or a five-day hike takes visitors into the heart of the Maya world in Yucatán, from Dzoyaxché, a small community built around the faded yellow walls of a 19th-century hacienda some 15 miles south of Mérida, to the excavated temples of Mayapán, one of the last great Maya capital cities.

But how to harness flies to maintain — and boost — food production? One way is to attract more of them to fields and orchards. Schemes that encourage farmers to plant wildflowers, keep remnant native vegetation and leave grasslands uncut can be very effective at increasing the number and diversity of insects and expanding the pool of potential pollinators. Hoverflies and blowflies need a few extras if they are to proliferate, though: carrion for blowflies, access to aphids for some hoverflies and ponds or streams containing dung, decaying vegetation or carcasses for others.

Mango growers realized way back that flies are important pollinators. “Some encourage flies by hanging large barrels from their trees and putting roadkill in them,” Finch says. “Other guys bring in a ton of fish and dump it in a heap in the middle of the orchard.” The farmers are convinced that the pungent bait makes a difference, and the biology of blowflies suggests that it might. Yet there’s no scientific proof that it does.

At the outset, the park was an orphan idea with no clarity of purpose, no staff, no budget. Congress seemed to lose interest as soon as the ink of Grant’s signature dried. Yellowstone became a disaster zone, neglected and abused, for more than a decade. Nathaniel Langford, the failed bank clerk and railroad publicist, served as its first superintendent, at zero salary, and during his five years in the post he barely earned that, revisiting the park only two or three times. Market hunters established themselves brazenly in the park, killing elk, bison, bighorn sheep, and other ungulates in industrial quantities. By one account, a pair called the Bottler brothers shot about 2,000 elk near Mammoth Hot Springs in early 1875, generally taking only the tongue and the hide from each animal, leaving the carcasses to rot or be scavenged. That account doesn’t say how many grizzly bears the Bottlers killed over those carcasses, for convenience or profit, but undoubtedly the elk meat was a dangerous attractant that brought bears near guns. An elk hide was worth six to eight dollars, serious money, and a man might kill 25 to 50 elk in a day. “There was this massive slaughter that occurred here, from 1871 through at least 1881,” according to Lee Whittlesey, currently Yellowstone’s historian. Antlers littered the hillsides. Wagon tourists came and went unsupervised, at low numbers but with relatively high impact, some of them vandalizing geyser cones, carving their names on the scenery, killing a trumpeter swan or other wildlife for the hell of it. Ungulate populations fell, and then the carnage gradually petered out, Whittlesey told me, “until the Army arrived here in 1886.”

The Yosemite Valley in California, which earlier had been granted to that state for protection as a state park, served as a rough precedent; Niagara Falls back in New York, on the other hand, stood as a negative paradigm. Niagara was infamous to anyone who cared about America’s natural majesties, because private operators there had bought up the overlooks and blocked the views, turning that spectacle into a commercial peep show. Yellowstone, as a great public attraction promising to bring visitors and money westward, would be different.

This is the paradox of Yellowstone, and of most other national parks we have added since: wilderness contained, nature under management, wild animals obliged to abide by human rules. It’s the paradox of the cultivated wild. At a national park in Africa—Serengeti in Tanzania, for instance, or Masai Mara game reserve in Kenya, Kruger in South Africa—you wouldn’t face such ambiguity. You would view the dangerous beasts, the lions and elephants and leopards and buffalo, from the safety of your Land Rover or your safari van, seldom if ever strolling through their habitat on foot. But in America we’ve chosen to do things differently, and Yellowstone, because it’s the first national park, an iconic place known throughout the world, which millions of people visit each year, is where the paradox is most powerfully played out.

The real lesson inherent in the death of Lance Crosby, and in the equally regrettable death of the bear that killed him, is a reminder of something too easily forgotten: Yellowstone is a wild place, constrained imperfectly within human-imposed limits. It’s a wild place that we have embraced, surrounded, riddled with roads and hotels and souvenir shops, but not tamed, not conquered—a place we treasure because it still represents wildness. It’s filled with wonders of nature—fierce animals, deep canyons, scalding waters—that are magnificent to behold but fretful to engage. Most of us, when we visit Yellowstone, see it as if through a Plexiglas window. We gaze from our cars at a roadside bear, we stand at an overlook above a great river, we stroll boardwalks amid the geyser basins, experiencing the park as a diorama. We remain safe and dry. Our shoes don’t get muddy with sulfurous gunk. But the Plexiglas window doesn’t exist, and the diorama is real. It’s painted in blood—the blood of many wild creatures, dying violently in the natural course of relations with one another, predator and prey, and occasionally also the blood of humans. Walk just 200 yards off the road into a forested gully or a sagebrush flat, and you had better be carrying, as Lance Crosby wasn’t, a canister of bear spray. Your park entrance receipt won’t protect you. You can be killed and eaten. But if you are, despite the fact that you have freely made your own choices, there may be retribution.

Grizzly bears, clearly, can be dangerous animals. But the danger they represent should be seen in perspective: In the 144 years since Yellowstone was established, more people have died there of drowning and of scalding in thermal pools, and of suicide, than have been killed by bears. Almost as many people have died from lightning strikes. Two people have been killed by bison.

On August 7, 2015, in Yellowstone National Park, a ranger found the chewed-upon body of a man near a hiking trail not far from one of the park’s largest hotels. The deceased was soon identified as Lance Crosby, 63 years old, from Billings, Montana. He had worked seasonally as a nurse at a medical clinic in the park and been reported missing by co-workers that morning.Investigation revealed that Crosby was hiking alone on the previous day, without bear spray, and ran afoul of a female grizzly with two cubs. The sow, after killing and partially eating him (not necessarily in that order), and allowing the cubs to eat too, cached his remains beneath dirt and pine duff, as grizzlies do when they intend to reclaim a piece of meat. Once trapped and persuasively linked to Crosby by DNA evidence, she was given a sedative and an anesthetic and then executed, on grounds that an adult grizzly bear that has eaten human flesh and cached a body is too dangerous to be spared, even if the fatal encounter wasn’t her fault. “We are deeply saddened by this tragedy and our hearts go out to the family and friends of the victim,” said Park Superintendent Dan Wenk, a reasonable man charged with a difficult task: keeping Yellowstone safe for both people and wildlife. 

In damselfish, scientists have discovered an exceedingly rare kind of agriculture involving the first known case of a nonhuman vertebrate domesticating another animal. Longfin damselfish raise, and live on, algae that they farm on coral reefs. “The algae that grow in those gardens really can’t grow anywhere else, they are vulnerable to being outcompeted by other kinds of algae,” says Strassmann. But the fish also herd swarms of tiny mysid shrimp, floating clusters that fertilize the algae with their waste to provide a better crop. In turn, the damsel fish protect these farmer’s helpers from being eaten by other fish species. “It’s hard to evolve a new trait, it’s a lot easier to capture someone else that already has that trait. That’s really what’s going on here,” says Strassmann.

Instead of going out there and finding food, and eating it, you are cultivating your own food.”

But it turns out that we’re not so unique after all. In fact, compared to some species, humans are late to the game. Ants began farming fungi a staggering 65 million years ago, soon after the days of the dinosaurs. Ambrosia beetle and termite species have also raised such crops for eons—as evidenced by a 25 million-year-old fossilized nest. Damselfish cultivate gardens of algae, and some ants have even developed a form of animal husbandry that includes shepherding stocks of aphids and mealy bugs.

Generations of students have learned that the dawn of settled agriculture, some 12,000 years ago, was a revolutionary change in human social development. When our ancestors domesticated plants and animals they created reliable food supplies, and with them grew cities and the fruits of advanced civilization and culture. Farming, we believed, was one of the things that set us apart.

A growing body of research reveals that looking at their eyes may be a neglected and powerful way to do so. The phrases “the eyes are the window to the soul” and “I can see it in your eyes” certainly sound poetic. Many singers, songwriters and writers have capitalized on it. But it turns out that the eyes really might be the windows to the soul. And here’s the great thing about eyes: even if people don’t want you to know how they feel, they can’t change how their eyes behave. So how does this work? The first thing to look for is changes in pupil size. A famous study published in 1960 suggests that how wide or narrow pupils are reflects how information is processed, and how relevant it is. In their experiment, the two experimental psychologists Hess and Polt of the University of Chicago asked male and female participants to look at semi-nude pictures of both sexes. Female participants’ pupil sizes increased in response to viewing men, and male participants’ pupils increased in response to viewing women.

It is often easier to access someone else’s heart than their mind. We can nearly effortlessly pick up on our partner’s mood or sense that a friend dismisses our plans, without them even speaking a word. But how do we know what is going on in their heads? How do we get this special access to the most private of domains—the human mind?

Cole suggests that assessing language use could help to test whether interventions aimed at reducing stress really work. Perhaps “you could even ditch self-report stress measures”, he says, and instead listen passively to how trial participants speak.

People with more stressed-out gene-expression signatures tended to talk less overall. But they used more adverbs such as 'really' or 'incredibly'. These words may act as “emotional intensifiers”, says Mehl, signifying a higher state of arousal. They were also less likely to use third-person plural pronouns, such as 'they' or 'their'. That makes sense too, he says, because when people are under threat, they may focus less on others and the outside world.

He was particularly interested in what psychologists call 'function' words, such as pronouns and adjectives. “By themselves they don’t have any meaning, but they clarify what’s going on,” says Mehl. Whereas we consciously choose 'meaning' words such as nouns and verbs, researchers believe that function words “are produced more automatically and they betray a bit more about what’s going on with the speaker”. Mehl and others have found, for example, that people’s use of function words changes when they face a personal crisis or following terrorist attacks.

Adverse life circumstances—such as poverty, trauma or social isolation—can have devastating effects on health, increasing the risk of a variety of chronic disorders ranging from heart disease to dementia. Researchers trying to pin down the biological mechanisms involved have found that people who experience these circumstances also undergo broad changes in gene expression in the cells of their immune system. Genes involved in inflammation become more active, for example, and antiviral genes are turned down.

Psychologists found that tracking certain words used by volunteers in randomly collected audio clips reflected stress-related changes in their gene expression. The speech patterns predicted those physiological changes more accurately than speakers’ own ratings of their stress levels.

Efforts to bring back the thylacine do have an advantage though, Pask says, which is that the animal’s extinction was relatively recent. Scientists have a comprehensive biobank of information on the species as well as museum and laboratory samples, including skulls, skeletons, scat, and even preserved embryonic young originally found in their mothers' pouches.

The available thylacine genome is fragmentary, however, and filling in some of the gaps remains a challenge. It could be more complex to genetically engineer a proxy thylacine than a proxy woolly mammoth, for example, because the latter is more closely related to its living mold, the Asian elephant, than the thylacine is related to the numbat.

Any de-extinction project needs to start with the closest living relative to the animal in question, Pask says. The thylacine’s closest living relative is the numbat, a small insectivorous marsupial native to Western Australia whose genomic sequence was decoded earlier this year.

The scientists behind the project believe that bringing the creature back would restore ecological balance to the island of Tasmania by re-introducing a top predator that kept other animals in check. The work could also help develop technology, such as genetic engineering tools and artificial wombs, that could support other conservation work.

The lab-created animals would not be the exact species that went extinct, but hybrids of those species with their DNA filled in by living relatives. The most well-known de-extinction project is an effort to bring back a version of the woolly mammoth by splicing its genome with Asian elephant DNA. The work has been a longtime project of Harvard geneticist George Church, who recently co-founded the bioscience company Colossal, with $75 million in private funding, to accelerate the research.

A radical idea to support the recovery of damaged ecosystems has been gathering steam: resurrect species that have gone extinct and reintroduce them to the wild. Proponents of “de-extinction” argue that by returning species that played an important ecological role to their old habitats, entire regions could benefit.

The eight planets (sorry, Pluto) orbit the sun along a plane. From our position on Earth, it appears as if the sun is tilted at a six-degree angle against that plane. But according to Dr. Brown, it’s actually the planets that are tilted, because of Planet Nine’s gravity. He said it was one of many effects that the elusive planet had on the solar system, and a clue to proving its existence.Video

Earlier this year Michael Brown, a professor of planetary astronomy at the California Institute of Technology, presented evidence that there may be a massive planet beyond Neptune orbiting the sun. The so-called Planet Nine is thought to be about 10 times the mass of Earth and about as large as Neptune. At its farthest point it is about 155 billion miles away from the sun.

Most people think the eight planets in our solar system orbit the sun along a straight plane, like a disc on a record player. But actually, that plane is slightly tilted, and now astronomers think they know why: The elusive Planet Nine.