While we all try to find happiness, sometimes we still end up feeling low. While most people can control this feeling, low moods can stay with some, leading to depression. About 322 million people suffered from depression in 2015, according to a report by the World Health Organization in February. This is more than 4 percent of the world's population.

    Depression is described by the WHO as a mental disorder. It has several symptoms including sadness, loss of interest and feelings of low self-worth. In severe cases, depression may even lead to suicide.

    The number of people living with depression is increasing. The WHO reported a rise of 18.4 percent between 2005 and 2015. Young people are a group known to suffer with depression. “The pressures on today's youth are like no other generation, perhaps,” Dan Chisholm, an official of WHO, told Reuters.

    In China, depression among young people is on the rise, Zhu Zhuohong, a psychology professor with the Chinese Academy of Sciences, told Xinhua News Agency. Competition to outperform others, especially in education, can cause a lot of pressure for Chinese youth.

    Almost 1.2 million Chinese people aged 15 to 24 suffer from depression, according to a report released by British science journal The Lancet in May.

    Luckily, more and more efforts are being made to deal with this problem. This year's World Health Day, held on April 7, will focus on depression. The day will highlight (强调) the “Depression: let's talk” campaign. The campaign aims to make sure that people with depression both seek and get help.

    Elephants in Uganda are starting to come close to villages near national parks. The big animals are a real danger to people.

    So, the Uganda Wildlife Authority has been giving people new tools to keep the elephants away: vuvuzelas. They are plastic instruments some fans use at sports events.

    The instruments make a loud sound elephants do not like. The animals leave, and no one is harmed. A spokesperson for the Uganda Wildlife Authority says vuvuzelas work because they do not threaten the elephants. That is important because an elephant that feels threatened is more likely to attack. So far, no one has reported an elephant attacking in answer to a vuvuzela.

    Officials and villagers have tried other ways to stop elephants from coming near farms and houses. They have built beehives – houses for flying insects that sting. They have hung ropes covered in spicy oil. They have dug long, deep holes. And they have used guns, called A-K47s.

    An official from the Uganda Wildlife Authority explains that people shoot the gun in the air to scare the elephant. But over time, the elephants have stopped being afraid of the sound of the gun. They only look at the shooter and wave their ears.

    Another official for the Uganda Wildlife Authority, Gessa Simblicious, says one elephant-prevention solution will not work everywhere in Uganda. And one day, elephants may accept the vuvuzela noise, just as they do the sound of the A-K47.

    But right now, vuvuzelas are an effective, non-violent and fun way to deal with a serious problem.

    Back in 1988, Red Delicious made up 70 to 80 percent of the domestic apple market. Over the years, farmers sold a lot of them because they looked great. But they had a floury texture (质地), and people want an apple that's firm, crisp(脆的)and juicy. I started searching for one. By 1994, threatened by varieties from Japan and New Zealand, the U.S. apple industry and Washington State University agreed that we had to grow our own.

    First, we cross-pollinated(授粉) existing apples: Collect pollen from one flower, put it on the tip of a pencil eraser, and rub it into another. We crossed dozens of crisp, tasty varieties such as Gala, Fuji, and Pink Lady. But the best breed came out of Honey Crisp and Enterprise parents. We grew the cross-bred seeds into 5-foot trees, grafted those to rootstocks(根茎) to make them start producing quickly, and planted them in evaluation gardens. A few years later, they fruited—and we began tasting.

    So I would walk down long rows of hundreds and thousands of trees, and when I found an attractive fruit, I'd bite, chew, spit it out. Most were terrible, but when I found one with good texture and taste, I'd pick 10 or 20 of them. Then I put them in cold storage to see how they would hold up after a few months. After that, three or four researchers sat down and tasted every apple. We checked acidity and sugar levels, which can break down over time, and tested firmness and crispness using instruments that measure pressure and cell breakdown.

    When we found exactly what we wanted, we planted and tested them all over again. Eventually, we ended up with the Cosmic Crisp. It can spend nine to 12 months in storage, and stay crisp, firm, juicy and sweet.

    Siblings refer to one's brothers and sisters. We're attached to siblings as adults far longer than we are as children. Our sibling relationships, in fact, are the longest-lasting family ties we have.

    “Paul, my younger brother, and I, kind of annoyed each other when we were kids,” said Anna, an interviewee, “But as adults, we've always had each other's back, especially when dealing with our mother's health crisis. Paul is the first person I want to talk to when something worries me.”

    There's probably a biological explanation for the close bond of the sibling relationship. Siblings share half their genes, which biologists say should be motivation enough for each other's devotion.

    One thing that can weaken closeness in adulthood is a parent who played favorites in childhood; this sense of hatred can last a lifetime. The simple concept of parental favoritism was enough to shake their relationship.

    “What Paul and I are pretty sure is our parents treated us the same when we were growing up. Yet we're very different people,” Anna said,“ Paul is outgoing while I'm shy. Paul is an amateur pianist while I can't read music or carry a tune. In families with more than one child, every sibling seems to get a label in contrast to every other sibling.”

    The very presence of siblings in the household can be an education. When a new baby is born, the older sibling gains social skills by interacting with the younger, and the younger gains cognitively（认知角度地）by imitating the older. They learn from the friction between them, too, as they fight for their parents' attention. Mild conflict between brothers and sisters teaches them how to interact with friends and co-workers for the rest of their lives.

    It's so sad when things between siblings fall apart, which happens when aging parents need care or die — old feelings of contradiction and jealousy erupt all over again. Many families get through their parents' illnesses just fine, establishing networks where the workload is divided pretty much equally. But about 40 percent of the time there is a single primary caregiver who feels like she is not getting any help from her brothers and sisters, which can lead to serious conflicts.

    Throughout adulthood, the sibling relationship “is powerful and unchanged,” said Jane Mersky Leder, author of the new e-book The Sibling Connection. Whether we are close to our siblings or distant, she writes, they remain our brothers and sisters — for better or for worse.

    So remember the immortal（永恒的）words of folksinger Loudon Wainwright Ⅲ, in a song called Thanksgiving.“ On this brilliant occasion, this special family dinner, if I argue with a loved one, please make me…”

    More than two thirds of the world's polar bears will be wiped out by 2050, according to a shocking new study. By then, scientists say, global warming will have melted 42 percent of the Arctic sea ice. By 2100, only a very few of these important creatures will be left.

    The report has been produced by the US Geological Survey. The scientists have publicized their findings in the hope of influencing US Interior Secretary Dirk Kempthorne, who has been asked to put polar bears on the US endangered species list.

    Polar bears depend on floating sea ice as a platform for hunting seals, which are their main food. Without enough ice, polar bears would be forced to go onto the land, where they are poorly skilled hunters, and would be unlikely to adapt to the life on the land in time. Experts say few little bears would survive and the stress could make many females unable to get pregnant.

    The team of American and Canadian scientists spent six months studying bears, on the ground, from spotter planes and in the lab, using computer models. Some team members fear the result is even worse for the bears than what their report says. They say the Arctic is warming faster than anywhere in the world and much faster than their computer had been forecasting. Satellite observations have showed that the ice has decreased to an all­time low.

    However, not everyone in the scientific community believes that global warming is happening on such an alarming scale. Another investigation has found that polar bears are still being hunted by wealthy “sportsmen” who want their skins and heads. At least ten international companies offer bear­hunting trips.

    Humans and elephants don't always get along. In Africa and Asia, elephants damage equipment, farmers' crops, and natural habitat for other species. If an elephant becomes a problem, humans may kill it. So local people and animal protectionists are trying to find better ways to keep elephants away from sensitive places. Now, researchers think they have a good tool to prevent elephants: honeybee pheromones (信息素).

    “Elephants dislike being stung(叮咬) in the trunk, because it's an extremely sensitive organ. Imagine being stung in your nose by a bee, and multiply that a few thousand times.” said Mark Wright, a professor at the University of Hawaii.

    Kenyan farmers have long known that if they hang live beehives (蜂箱) around their farms, they will drive elephants away. The problem is how to manage hundreds of thousands of hives, if you have a huge area to protect. And then the idea came up to look at the alarm pheromones, which are chemicals that the bees release to launch an attack on something that's damaging the hive.

    So the researchers tested out an artificial mixture of chemicals that imitates (模仿) honey bees' alarm pheromones. The researchers hung white socks treated with the artificial mixture as well as untreated control socks around an elephant watering hole, and then observed the animals' behavior. “Elephants are really curious creatures. They'll walk along and see something like a sock hanging on a branch. If it's not treated with the alarm pheromones, they'll pick it up, throw it around, and try to taste it, things like that. And in the case of the treated ones, they would show immediate signs of unease or uncertainty, and they'd eventually back off from them.”

    In order to avoid the elephants more effectively, the researchers plan to make the pheromone mixture purer. That way, elephants will stay far away from wherever they should not be going-and both elephants and humans can coexist a bit more peacefully.