No student of a foreign language needs to be told that grammar is complex. By changing the order of the words and by adding a range of auxiliary verbs (助动词) and suffixes (后缀), we can turn a statement into a question, state whether an action has taken place or is soon to take place, and perform many other word tricks to convey different meanings. However, the question which many language experts can't understand and explain is—who created grammar?

    Some recent languages evolved due to the Atlantic slave trade. Since the slaves didn't know each other's languages, they developed a make-shift language called a pidgin. Pidgins are strings of words copied from the language of the landowners. They have little in the way of grammar, and speakers need to use too many words to make their meaning understood. Interestingly, however, all it takes for a pidgin to become a complex language is for a group of children to be exposed to it at the time when they learn their mother tongue. Slave children didn't simply copy the strings of words used by their elders. They adapted their words to create an expressive language. In this way complex grammar systems which come from pidgins were invented.

    Further evidence can be seen in studying sign languages for the deaf. Sign languages are not simply a group of gestures; they use the same grammatical machinery that is found in spoken languages. The creation of one such language was documented quite recently in Nicaragua. Previously, although deaf children were taught speech and lip reading in the classrooms, in the playgrounds they began to invent their own sign system, using the gestures they used at home. It was basically a pidgin and there was no consistent grammar. However, a new system was born when children who joined the school later developed a quite different sign language. It was based on the signs of the older children, but it was shorter and easier to understand, and it had a large range of special use of grammar to clarify the meaning. What's more, they all used the signs in the same way. So the original pidgin was greatly improved.

    Most experts believe that many of the languages were pidgins at first. They were initially used in different groups of people without standardization and gradually evolved into a widely accepted system. The English past tense—“ed” ending— may have evolved from the verb “do”. “It ended” may once have been “It end-did”. It seems that children have grammatical machinery in their brains. Their minds can serve to create logical and complex structures, even when there is no grammar present for them to copy.

    When you see someone you know, the easiest way to recognize them is by their face—but not everyone can do this. Many people have prosopagnosia, or face blindness, which is a neurological（神经病学的）condition where the part of the brain that recognizes faces fails to develop. It can stop people recognizing partners, family members, friends or even their own reflection. It was once thought to be caused by brain injury (acquired prosopagnosia) but now a genetic link has been proved (development prosopagnosia).

    Acquired prosopagnosia is a very rare but as many as one in 50 people may have developmental prosopagnosia. There's no specific treatment, but training programmes are being developed to help improve facial recognition.

    For many, the situation can be dangerous. I've heard stories of people being robbed by strangers claiming to be family members, or of children wandering off strange men.

    It was only is this century that researchers began to realize exactly how many people in this world were quietly living with the condition.

    Like a blind person who can recognize family members by their footsteps, prosopagnosics are forced to develop unusual ways of discovering who it is they're meeting or talking to. From the obvious markers like hair and voice, to the way one sits, stands or walks, they rely on dozens of means to get through ordinary life.

    Faces are an important part of identity. Not to be recognized feels terrible—it's as if you've been overlooked, like someone's saying you don't matter. But it's nothing to the pain of knowing that you're hurting people's feelings constantly, and yet being completely unaware that you're doing it in the moment. To be alienated（隔离的）from the world of faces is a strange position to be in, but I'm comforted by the thought that articles like this will do a little to help people forgive me and others like me.

    Crossing your legs is an extremely common habit. While you may find it comfortable to sit with one knee crossed over the other, it might be causing health problems that you are not aware of.

    A study published in Blood Pressure Monitoring stated that sitting with your legs crossed can increase your blood pressure. The reason this happens is because the blood in your legs has to work against gravity to be pumped back to your heart, crossing one leg over the other increases resistance, making it even harder for the blood to circulate. You won't feel any immediate effects, but sitting for long periods of time will hurt you forever.

    Crossing your legs can also lead to neck and back pain. Ideally, it's best for our bodies to sit with our feet planted flat, hip width apart, on the floor, but it's not easy to maintain perfect posture all day at the office. When you sit with your legs crossed your hips are in a twisted position, which can cause one of your pelvic bones(骨盆) to rotate. Since your pelvic bone supports your neck and spine（脊椎）, this can cause pressure on your lower and middle back and neck.

    You also might notice that when you sit with your legs crossed for long periods of time your feet and legs get painful or have the feeling of being asleep. This is because when one leg sits on top of the other it causes pressure on the veins（静脉） and nerves in your legs and feet. It can cause numbness and/or temporary paralysis in the legs, ankles, or feet. While the feeling of discomfort may only last a minute or two, repeatedly crossing your legs until they feel numb can cause permanent nerve damage.

    So next time you sit down, try to get yourself in the habit of sitting with both of your feet on the floor. Not only will it help your posture and stability, but it will also save your health in the long run.

    Something's happening at the lowest point on our planet, some 1,388 feet below sea level. The Dead Sea, a salt lake close to Israel, Jordan and the West Bank, is shrinking at an alarming rate—about 3.3 feet per year, according to the environmentalist group EcoPeace Middle East.

    “It's not just like one country is punishing the Dead Sea; it's more like the whole region,” said photographer Moritz Küstner, who visited the area in February to work on his series “The Dying Dead Sea”.

    The Dead Sea needs water from the other natural sources surrounding it, such as the Jordan River basin. But around the 1960s, the courses of some water sources it relied upon were diverted. Israel, for instance, built a pipeline during that time so it could supply water throughout the country.

    Mineral extraction(提取)industries are another main reason why the water levels are declining, experts say. The Dead Sea's minerals have been popular for their medical power and can often be found in cosmetics(化妆品)and other consumer products.

    And then, of course, there's the Middle East's hot, dry climate, which makes it difficult for the lake to refill itself. Last year, Israel and Jordan signed a $ 900 million deal in an effort to stabilize the Dead Sea's water levels. It involves building a canal from the Red Sea to the Dead Sea which would be able to not only supply water to Israel and Jordan but also to pump much needed water—some 300 million cubic meters annually—into the Dead Sea.

    “This is the most important and significant agreement since the peace treaty with Jordan (in 1994),” said Silvan Shalom, Israel's energy and water resources minister at the time. Whether the canal—estimated to take three years to complete—will work out positively and as planned remains to be seen.

    For now, Küstner shows us that the Dead Sea remains very much a place of interest, with people from all over the world going there to swim in its salty waters.

    Escaping predators (食肉动物), digestion and other animal activities—including those of humans—require oxygen. But that essential ingredient is no longer so easy for marine life to obtain, several new studies reveal.

    In the past decade ocean oxygen levels have taken a dive—an alarming trend that is linked to climate change, says Andreas Oschlies, an oceanographer at the Helmholtz Center for Ocean Research in Germany, whose team tracks ocean oxygen levels worldwide. "We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are," he says. It is no surprise to scientists that warming oceans are losing oxygen, but the scale of the drop calls for urgent attention. Oxygen levels in some tropical (热带的) regions have dropped by an astonishing 40 percent in the last 50 years, some recent studies reveal. Levels have dropped less significantly elsewhere, with an average loss of 2 percent globally.

    A warming ocean loses oxygen for two reasons: First, the warmer a liquid becomes, the less gas it can hold. That is why carbonated drinks go flat faster when left in the sun. Second, as polar sea ice melts, it forms a layer of water above colder, more salty sea waters. This process creates a sort of lid that can keep currents from mixing surface water down to deeper depths. And because all oxygen enters the surface, less mixing means less of it at depth.

    Ocean animals large and small, however, respond to even slight changes in oxygen by seeking refuge in higher oxygen zones or by adjusting behavior, Oschlies and others in his field have found. These adjustments can expose animals to new predators or force them into food-scarce regions. Climate change already poses serious problems for marine life, such as ocean acidification, but deoxygenation is the most pressing issue facing sea animals today, Oschlies says. After all, he says, "they all have to breathe."

    Aside from food web problems, animals face various other physiological challenges as their bodies adjust to lower oxygen levels. Chinese shrimp (虾) move their tails less vigorously to preserve energy in lower oxygen environments. Some creatures, such as jellyfishes, are more tolerant of low oxygen than others are. But all animals will feel the impact of deoxygenation because they all have evolved their oxygen capacity for a reason, says Oschlies. "Any drop in oxygen is going to damage survivability and performance," he says.