1 . Most animal species in the world have developed some sort of natural camouflage that helps them find food and avoid attack. The specific nature of this camouflage varies considerably from species to species.

Camouflage develops differently depending on the physiology and behavior of an animal.    1    

An animal's environment is often the most important factor in what the camouflage looks like. The simplest camouflage technique is for an animal to match the "background" of its surroundings.

Since the ultimate goal of camouflage is to hide from other animals, the physiology and behavior of an animal's predators or prey is highly significant.     2    . For example, there’s no point in an animal replicating the color of its surroundings if is main predator is color-blind.

In addition to background-matching coloration, many animals have distinctive designs on their bodies that serve to conceal them. These designs, which might be spots, stripes or a group of patches, can help the animal in a couple of ways. First, they may match the pattern of "the model", the background of the animal's surroundings. Second, they may serve as visual disruptions. Usually, the patterns are positioned out-of-line with the body's contours (外形).     3    . This makes it hard for the predator to get a clear sense of where the animal begins and ends — the pattern on the body seems to nun of in every direction.

Other animals use a more aggressive sort of mimicry. Several moth species have developed striking designs on their wings that resemble the eyes of a larger animal. The back of the hawk moth caterpillar actually looks like a snake head, a frightening visage for most predators he moth would come across.

Mimicry is a different approach than ordinary camouflage, but it works toward the same end. By developing a certain appearance, an animal species makes itself a harder target for predators and a sneakier hunter for prey. As animal species evolve, they become more and more in tune with their environment.     4    . After all, being entirely overlooked by a predator is preferable to having to put up a fight.

2 . A breed of upstart apps is taking on an internet function that might seem unneeded or even ill—advised: helping teens talk to strangers.

Branded as “social discovery” services, these apps pitch themselves as alternatives to outlets that already specialize in online connections, like Facebook and Instagram. They say they are better at helping young users meet like —minded people outside their existing circles. And they say they have safeguards, such as separating users by age and using artificial intelligence, to protect against their appropriate or unsafe behavior that has plagued previous attempts to connect young people online.

Their user numbers suggest that, whether they succeed in striking the right balance, apps like Yubo and Hoop are tapping into a need among teens and 20 —somethings for new ways to branch out online.

“There is no place today to socialize online,” says Sacha Lazimi, the 26—year—old French co—founder of Yubo, which connects strangers with messaging and live streaming.

It is a counterintuitive statement for anyone who had seen teens sending Snaps rapid fire to their friends, responding to videos on TikToK, Face Timing for hours, or using Instagram. But Mr. Lazimi thinks those platforms allow for too much passive participation. “Snapchat, Instagram and Tik Tok are all about performance, content and individual”, he says.

Yubo features a swiping interface similar to that of Tinder. But Mr. Lazimi insists it is not adating app. The point, he says, is to facilitate communication between people all over the world who share mutual interests. Yubo isn’t present everywhere in the lives of American teens yet —and may be never will be—but the company says the app has 25 million users signed up, with nearly half of daily use now coming from America.

But some of these apps have also been the subject of safety concerns. Yubo has also faced its own safety challenges. In Florida, law—enforcement officially say they arrested a man who reportedly lured a teenager through Yubo.

In a statement, Yubo said that the prevention of child abuse has been a key priority for the past three years. “Yubo recognizes its responsibility in protecting young people using its service and has gone far beyond many of the main social media services.”

However, actually teens are doing more to protect themselves than many give them credit for, says Dr. Hinduja. “They are doing something to keep themselves safe or we would have strikingly more victimization than we do.”

5 . Recently I attended several meetings where we talked about ways to attract students and keep younger faculty members from going elsewhere. It seems higher education has become an industry of meeting-holders whose task is to “solve” problems — real or imagined. And in my position as a professor at three different colleges, the actual problems in educating our young people and older students have deepened, while the number of people hired — not to teach but to hold meetings — has increased significantly. Every new problem creates a new job for an administrative fixer. Take our Center for Teaching Excellence. Contrary to its title, the center is a clearing house (信息交流中心) for using technology in classrooms and in online courses. It's an administrative sham (欺诈) of the kind that has multiplied over the last 30 years.

I offer a simple proposal in response: Many of our problems — class attendance, educational success, student happiness and well-being — might be improved by cutting down the bureaucratic (官僚的) mechanisms and meetings and hiring an army of good teachers instead.

If we replaced half of our administrative staff with classroom teachers, we might actually get a majority of our classes back to 20 or fewer students per teacher. This would be an environment in which teachers and students actually knew each other. The teachers must be free to teach in their own way — the curriculum should be flexible enough so that they can use their individual talents to achieve the goals of the course.

Additionally, they should be allowed to teach, and be rewarded for doing it well. Teachers are not people who are great at and consumed by research and happen to appear in a classroom. Good teaching and research are not exclusive, but they are also not automatic companions. Teaching is an art and a craft, talent and practice; it is not something that just anyone can be good at. It is utterly confusing to me that people do not recognize this, despite the fact that pretty much anyone who has been a student can tell the difference between their best and worst teachers.

6 . Patients often come into my office and ask, “How can I look younger?” While I always suggest healthy living — a balanced diet and regular exercise — in order to look and feel younger, I have never thought of facial exercises as part of that plan. That is, until a recent study, published in JAMA Dermatology (皮肤学), showed promising results that routine facial exercise may slow the merciless tide of time.

The theory behind the study originates from the fact that a major part of facial aging is due to the loss of fat and soft tissue, which leads to the growth and spread of wrinkles. If we can lift weights at the gym and enlarge muscles in arms, why couldn’t the same be done for muscles in our faces, therefore to create a more youthful face?

The concept of facial exercise is not a new one. A simple Internet search will produce a lot of blog posts and books on the subject, as well as various programmes that promise to be the next fountain of youth. What the JAMA Dermatology researchers did in their study, which was the first of its kind, was to examine this question from a more strict scientific aspect. They enrolled 27 women between the ages of 40 and 65 to perform daily, 30-minute exercises for eight weeks, and then continue every other day for a total of 20 weeks.

Dermatologists who did not know the participants were asked to rate their photographs before and after the exercise. The dermatologists found an improvement in cheek fullness and estimated the age of the participants at 51 years of age at the start of the programme and 48 at the end of the 20-week study. Furthermore, all the participants felt improvement in their own facial appearance at the end of the study.

While these results seem exalting, the study has some obvious limitations. Of the 27 patients involved, 11 gave up before completing the study. One reason may be that the programme was to time-consuming, clocking in at 30 minutes a day. The overall small size of the study also limits its generalizability to the larger population. In addition, there was also no control group, which would have helped reduce the possibility that this improvement happened by chance.

It’s also hard to draw conclusions about the longevity of these results. Probably the exercises must be continued to keep their effects. But for how long? And how frequently? Which exercises are most effective? Most studies are need to answer these questions.

7 . Last year, 138,000 San Francisco residents used Airbnb, a popular app designed to connect home renters and travelers. It’s a striking number for a city with a population of about 850,000, and it was enough for Airbnb to win a major victory in local elections, as San Francisco voters struck down a debatable rule that would have placed time restrictions and other regulations on short-term rental services.

The company fiercely opposed the measure, Proposition F, with a nearly $10 million advertising campaign. It also contacted its San Franciscan users with messages urging them to vote against Proposition F.

Most people think of Airbnb as a kind of couch-surfing app. The service works for one-night stays on road trips and longer stays in cities, and it often has more competitive pricing than hotels. It’s a textbook example of the “sharing economy”, but not everyone is a fan.

The app has had unintended consequences in San Francisco. As the San Francisco Chronicle reported last year, a significant amount of renting on Airbnb is not in line with the company’s image: middle-class families putting up a spare room to help make ends meet. Some users have taken advantage of the service, using it to turn their multiple properties into vacation rentals or even full-time rentals. Backers of Proposition F argued that this trend takes spaces off the conventional, better-regulated housing market and contributes to rising costs.

“The fact is, widespread abuse of short-term rentals is taking much needed housing off the market and harming our neighborhoods,” said ShareBetter SF, a group that supported Proposition F. Hotel unions have protested the company’s practices in San Francisco and other cities, saying that it creates an illegal hotel system.

San Francisco is in the middle of a long-term, deeply rooted housing crisis that has seen the cost of living explode. Actually, explode is a generous term. The average monthly rent for an apartment is around $4, 000. Located on a narrow outcropping of land overlooking the bay, San Francisco simply doesn’t have enough space to accommodate the massive inflow of young, high-salaried tech employees flocking to Silicon Valley.

As the Los Angeles Times reported, some San Francisco residents supported the measure simply because it seemed like a way to check a big corporation. Opponents of Proposition F countered that the housing crisis runs much deeper, and that passing the rule would have discouraged a popular service while doing little to solve the city’s existing problems.