Tibetan people can survive on the roof of the world—one of the most inhospitable places that anybody calls home—thanks to a version of a gene that they inherited from a group of extinct humans called Denisovans, who were only discovered four years ago thanks to 41,000-year-old DNA recovered from a couple of bones that would fit in your palm. If any sentence can encapsulate why the study of human evolution has never been more exciting, it’s that one.
In 2010, Rasmus Nielsen from the University of California, Berkeley found that Tibetan people have a mutation in a gene called EPAS1, which helps them handle low levels of oxygen. Thanks to this mutation, they can cope with air that has 40 percent less oxygen than what most of us inhale, and they can live on a 4,000-metre-high plateau where most of us would fare poorly. To date, this is still “strongest instance of natural selection documented in a human population”—the EPAS1 mutation is found in 87 percent of Tibetans and just 9 percent of Han Chinese, even though the two groups have been separated for less than 3,000 years.
But when the team sequenced EPAS1 in 40 more Tibetans and 40 Han Chinese, they noticed that the Tibetan version is incredibly different to those in other people. It was so different that it couldn’t have gradually arisen in the Tibetan lineage. Instead, it looked like it was inherited from a different group of people.
By searching other complete genomes, the team finally found the source: the Denisovans! The Tibetan EPAS1 is almost identical to the Denisovan version. It’s now a Tibetan speciality, but it was a Denisovan innovation.
This discovery is all the more astonishing because we still have absolutely no idea what the Denisovans looked like. The only fossils that we have are a finger bone, a toe, and two teeth. Just by sequencing DNA from these fragments, scientists divined the existence of this previously unknown group of humans, deciphered their entire genome, and showed how their genes live on in modern people. Denisovan DNA makes up 5 to 7 percent of the genomes of people from the Pacific islands of Melanesia. Much tinier proportions live on in East Asians. And now, we know that some very useful Denisovan DNA lives on in Tibetans.
Svante Paabo, who sequenced the Denisovan genome, is delighted. “It’s very satisfying to see that gene flow from Denisovans, an extinct group of archaic humans which we discovered only four years ago, is now found to have had important consequences for people living today,” he says.
“It was a complete surprise,” says Nielsen. “It took years after the Denisovan genome was published for us to even try this, because we thought it was so far-fetched.”
The discovery also adds to a growing picture of human evolution—one involving a lot of cross-breeding. Humans evolved in Africa, and everyone outside that continent descends from a relatively small group of pioneers who left it at some point in our prehistory. These trailblazers were adapted to life on the tropical savannah. As they migrated, they experienced all the varied challenges that the world has to offer, such as extreme temperatures and new diseases.
At the time, the world was already populated by other groups of humans, like Neanderthals and Denisovans. As the African immigrants met up with these groups, they had sex. And through these liaisons, their genomes became infused with DNA from people who had long adapted to these new continents. “It’s a new way of thinking of human evolution—a network of exchange of genes between many lineages,” says Nielsen.
Nielsen suspects that modern humans had sex with Denisovans in Asia, somewhere between 30,000 and 40,000 years ago. They inherited the Denisovan version of EPAS1, which lingered in the populations at very low frequencies. The carriers fared better at higher altitudes, and their descendants colonised the Tibetan plateau. This explains why the team found the Denisovan EPAS1 in the vast majority of Tibetans, but also in a couple of Han Chinese people living outside of Tibet.
Other scientists have shown that sex with Neanderthals could also have imported useful genes into our genome, including those involved in skin, hair, and the immune system. “What we’re learning from ancient genomes is that while each of them may have contributed only a little to our ancestry, those genetic streams were full of tiny golden nuggets of useful genes,” says anthropologist John Hawks, who emailed me just before visiting Denisova Cave where the Denisovan fossils were found.
“What is a bit surprising is that Denisova is not at high altitude,” says Hawks. It’s in the Altai mountains of Siberia, but it’s not that high up. If Denisovans had the high-altitude version of EPAS1, this could imply that they also spread through the more mountainous parts of China and South Asia. “This gives a route by which Denisovans might have gotten into Southeast Asia where we know modern humans picked up their genes on the way to Australia,” says Hawks.
Nielsen adds that the Denisovans weren’t necessarily adapted to high altitudes. Their version of EPAS1 could have helped them in other ways, and coincidentally allowed the Tibetans to colonise the roof of the world.
If I travelled to the Tibetan plateau, my body would try to cope by making more red blood cells, which transport oxygen around my body. But I’d overcompensate and make too many of these cells. My blood would become thick and viscous, leaving me prone to high blood pressure and stroke. Tibetans don’t have this problem. Their EPAS1 stops them from overproducing red blood cells and helps them acclimatise to the altitude without doing themselves harm. But cold climates can also raise blood pressure by constricting blood vessels. So perhaps the Denisovan version of EPAS1 helped them to adapt to extreme cold, rather than a lack of oxygen.
“To give you a definitive answer, I’d need to find a Denisovan and do some physiological experiments,” he says. “And I can’t.”
Eyes are testaments to evolution’s creativity. They all do the same basic things—detect light, and convert it into electrical signals—but in such a wondrous variety of ways. There are single and compound eyes, bifocal lensesand rocky ones, mirrors and optic fibres. And there are eyes that are so alien, so constantly surprising, that after decades of research, scientists have only just about figured out how they work, let alone why they evolved that way. To find them, you need to go for a swim.
This is the eye of a mantis shrimp—an marine animal that’s neither a mantis nor a shrimp, but a close relative of crabs and lobsters. It’s a compound eye, made of thousands of small units that each detects light independently. Those in the midband—the central stripe you can see in the photo—are special. They’re the ones that let the animal see colour.
Most people have three types of light-detecting cells, or photoreceptors, which are sensitive to red, green and blue light. But the mantis shrimp has anywhere from 12 to 16 different photoreceptors in its midband. Most people assume that they must therefore be really good at seeing a wide range of colours—a “thermonuclear bomb of light and beauty”, as the Oatmeal put it. But last year, Hanna Thoen from the University of Queensland found thatthey’re much worse at discriminating between colours than most other animals! They seem to use their dozen-plus receptors to recognise colours in a unique way that’s very different to other animals but oddly similar to some satellites.
Thoen focused on the receptors that detect colours from red to violet—the same rainbow we can see. But these ultra-violent animals can also see ultraviolet (UV). The rock mantis shrimp, for example, has six photoreceptors dedicated to this part of the spectrum, each one tuned to a different wavelength. That’s the most complex UV-detecting system found in nature. Michael Bok from the University of Maryland wanted to know how it works.
In the course of my travels–and my career as a promoter and practitioner of sustainable tourism–one question comes up again and again: “What can I do to be a more responsible traveler?” So I thought I’d pen a primer.
Here are seven things globetrotters can do to lessen their impact on the planet:
1. Avoid the plane and take the train (when possible).
Become part of the emerging “slow travel” trend by going to fewer places and spending more time in each. Train travel is a good way to do this. Not only will you experience a deeper sense of place, you’ll also decrease your carbon footprint. Some of my favorite travel-by-train destinations include India, Southeast Asia, East Africa, and China.
2. Give, the right way. Many well-intentioned travelers bring sweets, used clothing, books, and pencils to hand out to children and villagers in developing nations. Sadly, this kind giving often has unintended consequences–it can sew community conflict and encourage a culture of dependency and begging. I watched two Maasai women in Africa fight over a T-shirt that a smiling tourist had handed out; in some parts of Asia, the first English words children learn are “Give me sweet.”
It is better to give–be it money or goods–to reputable local organizations that work on social welfare programs, or to international groups that partner with them. A good one is Pack for a Purpose.
3. Understand the following two terms and be part of the new age of intelligent travel:
> Ecotourism: Two decades ago, I joined a dozen scientists, conservationists, and modern-day explorers in an old farm house outside of Washington, D.C. It was the first board meeting of the International Ecotourism Society.
Our task? To define what, exactly, ecotourism was. After two days, we agreed on what is now the most widely used definition of ecotourism in the world today: “Responsible travel to natural areas that conserves nature and sustains the wellbeing of local people.”
> Sustainable Tourism: This movement takes ecotourism’s core principles and applies them across the full spectrum of the travel and tourism industry–from city hotels to cruise lines. The three pillars of sustainable tourism are employing environmentally friendly practices (reduce, reuse, recycle); protecting cultural and natural heritage (e.g., restoring historic buildings or saving endangered species); and providing tangible social and economic benefits for local communities (ranging from upholding the rights of indigenous peoples to supporting fair wages for employees).
4. Say no to plastic. The Great Pacific Garbage Patch, a swirling mass of human trash stretching across thousands of miles of the ocean, includes gazillions of throw-away plastic bottles and bags that will take hundreds of years, if ever, to break down–all the while wreaking havoc on marine ecosystems.
Be a part of the solution by opting for locally purified water in recyclable glass bottles (in the tropics, I rely mainly on green coconuts to stay hydrated) and carrying tote bags in your luggage that you can use while perusing street markets and shops. Not only will this cut back on plastic waste, it will also reduce your carbon footprint–petroleum-based ingredients are a staple in manufacturing plastic bottles and bags.
5. Do your research when it comes to tour operators. I explore on my own most of the time when I travel, but when I do seek out the services of a tour outfitter, I always ask three questions before signing on: What are some of your tour company’s environmentally friendly practices? Can you give me an example of how your trips help to protect and support wildlife or cultural heritage? Do you employ local guides on your trips?
These days, any outfitter that cannot provide a clear answer is behind the times. Find another one.
6. Support the real local economy. Locally made crafts and souvenirs are not always cheaper, but purchasing them ensures your contribution to the economy will have a more direct and positive impact.
In Cancun, for example, some gift shops sell “traditional” Mexican sombreros that are imported from China because they cost less, while village artisans who make the hats by hand charge more. The difference is not just in the price. Buying the real sombreros supports authentic cultural heritage and provides needed jobs for the locals who make them.
7. Never buy wildlife products–period. On a trip to Vietnam’s Halong Bay, I watched a group of American tourists haggling with villagers who were selling some of the most beautiful sea shells I have come across in my travels.
Similarly, in Mongolia, I witnessed a couple of backpackers bargain in an outdoor market to buy a hand-stitched eagle hunter’s hat made from plush wolf fur. These travelers were inadvertently helping to support a growing marketplace for trafficking rare and endangered wildlife products as souvenirs. Just say no.
A stunning photo snapped by astronauts aboard the International Space Station shows Hurricane Arthur churning off the coast of Florida, heading north.
The image, taken on Wednesday morning (July 2) by a crewmember of the orbiting lab’s current Expedition 40, actually captures Arthur when it was still classified as a tropical storm. (Arthur strengthened to hurricane status early Thursday.)
“Surrounded by bright green waters, the Bahamas Islands are south of the storm in the lower right corner of the photo,” NASA officials wrote in adescription of the picture. “The U.S. coastline stretches along the left side of the photo.”
Robotic eyes are keeping tabs on Arthur from orbit as well. NASA’s Aqua satellite took a picture on Wednesday afternoon as it passed over the storm, for example, revealing that Arthur’s eye was still covered by clouds at the time.
Credit: NASA Goddard MODIS Rapid Response Team
Aqua has also been gathering data on Arthur in infrared light. One infrared image captured Thursday (July 3) shows thunderstorms around the storm’s center with temperatures around minus 63 degrees Fahrenheit (minus 53 degrees Celsius), NASA officials said.
Arthur is the first tropical storm of the 2014 Atlantic hurricane season. It took shape off southern Florida on Tuesday (July 1) and is currently heading north off the East Coast.
As of Thursday afternoon, Arthur was about 70 miles (113 kilometers) south-southwest of Cape Fear, North Carolina and featured maximum sustained winds of 90 mph (150 km/h). The National Hurricane Center (NHC), which is run by the U.S. National Weather Service, has issued a hurricane warning for areas from Surf City, North Carolina north to the Virginia border.
Arthur will likely come close to North Carolina’s Outer Banks later Thursday and early Friday (July 4) but should then turn to the northeast, forecasters say.
The storm is expected to be a Category 2 hurricane when it passes over or near the North Carolina coast, NHC officials said in an advisory Thursday. (Meteorologists classify hurricanes based on wind speed from Category 1, the weakest, to Category 5, the most powerful.) But Arthur should begin weakening Friday night and will likely be downgraded to a “post-tropical cyclone” on Saturday (July 5), they added.
With 6 colored sides, 21 pieces and 54 outer surfaces, there’s a combined total of over 43 quintillion different possible configurations. To put that into perspective: if you turned the Rubik’s cube once every second it would take you1400 trillion yearsto finish to go through all the configurations.If you had started this project during the Big Bang, you still wouldn’t be done yet.
Another way to think about this is, if a person had as many Rubik’s cubes as there were possible configurations, they could cover the surface of the Earth 275 times. And if one considers the number of configurations you could reach by disassembling and reassembling the cube, the number would be nearly 12 times that many
You may have heard of frozen grapes as a tasty snack, but what about heating grapes in the microwave? You probably shouldn’t try this one. It turns out that grapes react very oddly when they’re microwaved.
Since grapes are full of moisture, when they are microwaved, that moisture turns to steam. If the stem is still attached to the grape and there is nowhere for the steam to escape, it will explode slightly and rupture the skin.
If you place two grapes close together with their stem holes facing each other, some arcing and sparking will occur. If there is just a single grape with its stem hole open, it will let out a stream of steam. Good thing we don’t serve grapes warm.