Getting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt.

    In the early 16th century, people thought that dirt on the skin was a means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken a bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out.

    Though the belief in the merit of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientifically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War II. Advertisements repeatedly sell the idea; clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far?

    Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warn their children off touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist (免疫学家), encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground.

    The US teenager Thomas Cheatham had planned to study Latin during his time at Hebron High School in Texas. But when he learned that the school district was going to offer a Mandarin class, he quickly changed his mind.

    “I thought Mandarin would be more beneficial than Latin,” said Cheatham, who is now in his second year of studying the language. He speaks Mandarin to order food at Chinese restaurants and can read social media posts from his Chinese-speaking friends.

    While it's a difficult language to master, the high school junior, who plans to study computer engineering, thinks it will be important for his career. “Chinese is a good language to know, especially with China becoming a growing power,” he said.

    Many experts agree that proficiency in a language spoken by a billion people worldwide will give American students an edge in the global economy. “People are looking at China as our next economic competitor, and interest in Mandarin is growing,” said Marty Abbott, executive director of the American Council on the Teaching of Foreign Languages. “We're seeing it in all parts of the country. ”

    Abbott estimates that as many as 100, 000 students are now studying Mandarin throughout the US, in public and private schools. She said the US government has designated (指定) Mandarin as a “critical needs” language and provides professional development programs for teachers. “Our government wants to increase our language competency for national security and economic competitiveness,” Abbott said.

    At the same time, the Chinese government is spreading knowledge of the Chinese language and culture through Confucius Institutes established in many US states. For example, the Confucius Institute at the University of Texas in Dallas has been the home of a Confucius Institute for 10 years. It sponsors Confucius Classrooms at 21 local public and private schools, where tens of thousands of students are learning Mandarin.

Wilderness

    "In wilderness(荒野) is the preservation of the world." This is a famous saying from a writer regarded as one of the fathers of environmentalism. The frequency with which it is borrowed mirrors a heated debate on environmental protection: whether to place wilderness at the heart of what is to be preserved. 

    As John Sauven of Greenpeace UK points out, there is a strong appeal in images of the wild, the untouched; more than anything else, they speak of the nature that many people value most dearly. The urge to leave the subject of such images untouched is strong, and the danger exploitation(开发) brings to such landscapes(景观) is real. Some of these wildernesses also perform functions that humans need—the rainforests, for example, store carbon in vast quantities. To Mr.Sauven, these "ecosystem services" far outweigh the gains from exploitation.

    Lee Lane, a visiting fellow at the Hudson Institute, takes the opposing view. He acknowledges that wildernesses do provide useful services, such as water conservation. But that is not, he argues, a reason to avoid all human presence, or indeed commercial and industrial exploitation. There are ever more people on the Earth, and they reasonably and rightfully want to have better lives, rather than merely struggle for survival. While the ways of using resources have improved, there is still a growing need for raw materials, and some wildernesses contain them in abundance. If they can be tapped without reducing the services those wildernesses provide, the argument goes, there is no further reason not to do so. Being untouched is not, in itself, a characteristic worth valuing above all others.

    I look forwards to seeing these views taken further, and to their being challenged by the other participants. One challenge that suggests itself to me is that both cases need to take on the question of spiritual value a little more directly. And there is a practical question as to whether wildernesses can be exploited without harm.

    This is a topic that calls for not only free expression of feelings, but also the guidance of reason. What position wilderness should enjoy in the preservation of the world obviously deserves much more serious thinking.

    Some of the people who created many popular apps are telling kids to put their phones away — at least, a bit more often. The Center for Humane Technology is made up of people who used to work for big tech companies like Google, Facebook and Twitter. Now they want kids to stop using those apps and websites so much.

    In early February, the center started a campaign called The Truth About Tech. Its goal is to teach students, parents and teachers about the dangers of spending too much time on smart phones and computers.

    According to studies about kids and technology, more than 95 percent of elementary school-aged children spend at least part of every day using a computer or smart phone. About 78 percent of teens check their phones every hour, and more than half of them sleep with their phones in case they get a call or message during the night.

    The Center for Humane Technology says that the apps and websites we use every day are purposely designed to keep us chatting, playing or watching online as much as possible. That includes social media like Snapchat, Instagram, Facebook and Twitter, websites like YouTube and online games. It also says that the tech companies talk only about the good aspects of their products and don't mention the side effects.

    Some physical problems, like headaches, eyestrain (眼疲劳), and neck pain are caused by using phones or computers too much. Students spending too much time online may find it hard to be focused on school work. Children and teenagers are more likely to have these problems because their brains, bodies and social skills are still developing.

    One goal of The Truth About Tech campaign is to make sure that kids understand how technology affects them so they can make better decisions. The people behind the campaign also want governments and the tech companies themselves to take steps to protect children. When the leaders of the big technology companies are designing tech tools for kids, they should think about what they would want for their own children.

    Humans' invention of zero was vital for modern mathematics and science, but we're not the only species to consider “nothing” a number. Parrots and monkeys understand the concept of zero, and now bees have joined the club, too.

    Honey bees are known to have some numerical skills such as the ability to count to four, which may come in handy when keeping track of landmarks in their environment. To see whether these abilities extended to understanding zero, researchers trained 10 bees to identify the smaller of two numbers. Across a series of trials, they showed the insects two different pictures displaying a few black shapes on a white background. If the bees flew to the picture with the smaller number of shapes, they were given delicious sugar water, but if they flew toward the larger number, they were punished with bitter-tasting food.

    Once the bees had learned to consistently make the correct choice, the researchers gave them a new choice: a white background containing no shapes at all. Even though the bees had never seen an empty picture before, 64% of the time they chose it rather than a picture containing two or three shapes, the authors report today in Science. This suggests that the insects understood that “zero” is less than two or three. And they weren't just going for the empty picture because it was new and interesting. Another group of bees trained to always choose the larger number tended to pick the nonzero image in this test.

    In further experiments, the researchers showed that bees' understanding of zero was even more complex: for example, they were able to distinguish between one and zero-a challenge even for some other members of the zero club. Advanced numerical abilities like this could give animals an evolutionary advantage, helping them keep track of predators（捕食者）and food sources. And if an insect can display such a thorough grasp of the number zero, write the researchers, then this ability may be more common in the animal kingdom than we think.

    We hope you've finally made your peace with Pluto being downgraded from a planet to an ice dwarf (冰矮星)，because we have some more jarring news for you : It seems your teachers may have been wrong about the number of continents on the earth, too.

    Earlier this year, scientists published a report in the journal of the Geological Society of America detailing an eighth continent called Zealandia, roughly the size of India and almost completely hid itself under the Pacific Ocean east of Australia. Covering all of New Zealand as well as several nearby islands, Zealandia likely spent the best of its above-water days as part of the supercontinent Gondwana before fragmenting off Australia and Antarctica some 80 million years ago. This lost, underwater continent is just beginning to reveal its secrets, making for one of the most promising scientific discoveries this year.

    While researchers have been aware of the 1. 9 million-square-mile mass for two decades, Zealandia has only recently become the object of serious study since the Geological Society paper argued that it fits all the criteria for a proper continent, including a continental crust (地壳)that's distinctly separate from the seabed in terms of elevation, thickness, and geology. A team of 32 scientists from 12 countries just completed their first visit to six dig sites around Zealandia, where they drilled up more than 8,000 feet of sediment cores (沉积物岩心)that will help explain the lost continent's 80-million-year history.

    Because there is no official body that formally recognizes continents, whether or not Zealandia ends up in future geography textbooks will come down to its acceptance by the scientific community at large, possibly with a little help from travelers like you.