【推荐3】During most time of the 1930s, the Great Plains region was destroyed by drought and high winds. Howling across the Great Plains, these winds swept up the soil of the over-farmed land and created serious sandstorms of dust. These black sandstorms were so thick that daylight seemed more like dusk. Year after year having passed without rain, the winds continued to blow, and the dust swirled endlessly. During this terrible period, the region came to be called the Dust Bowl.

But the causes of the sandstorms weren’t just drought and winds. In a strange way, patriotism（爱国主义）was partly to blame. During World War Ⅰ, the U. S. government encouraged farmers to support the war by planting more wheat. As farmers increased their production, their own profits increased. Following the invention of the farm tractor, farmers plowed up thousands of acres of grassland and planted wheat. Wheat production rose fast, but nature soon turned success into disaster.

When the drought began, farmers didn’t realize that, by plowing up the grassland, they had destroyed the land’s natural protection against soil erosion（侵蚀）. As the drought continued, one powerful windstorm after another blew across the Great Plains. Crops dried up and were blown away.

Nothing grew for years. Eventually most of the rich topsoil（表土层）was blown away. As years passed, all the moisture（水汽）in the ground disappeared, leaving even the deep roots of trees in dust.

The Great Plains became a deserted place, as thousands of people fled to California to escape the dust and look for work. Most found only low-paying agricultural jobs. But there were those who refused to leave. For these farmers, a program encouraged them to make use of new ways that would protect the precious topsoil from eroding. But bringing the soil back to life took time, and the farmers still needed rain. Rain meant more to the farmers than it ever had before. It meant a future.

【推荐1】Until recently, several lines of evidence — from fossils genetics, and archaeology — suggested that humans first moved from Africa into Eurasia (the land of Europe and Asia) about 60,000 years ago, quickly replacing other early human species, such as Neanderthals and Denisovans, that they may have met along the way.

However, a series of recent discoveries, including 100,000-year-old human teeth found in a cave in China, have clouded this straightforward statement. And the latest find, a prehistoric jawbone at the Misliya Cave in Israel dating back to nearly 200,000 years ago, which is almost twice as old as any Homo sapiens (智人) remains discovered outside Africa, where our species was thought to have originated from, has added new and unexpected twist.

The find suggests that there were multiple waves of migration across Europe and Asia and could also mean that modern humans in the Middle East were interacting, and possibly mating, with other human species for tens of thousands of years. “Misliya breaks the mould (模式) of existing assumptions of the timing of the first known Homo sapiens in these regions,” said Chris Stringer, head of human origins at the Natural History Museum in London. “It’s important in removing long-lasting-constraint (限制) on our thinking.”

Prof. Hershkovitz, who led the work at Tel Aviv University said, “What Misliya tells us is that modern humans left Africa not 100,000 years ago, but 200,000 years ago. This is revolution in the way we understand the evolution of our own species.” He also added that the record now indicates that humans probably travelled beyond the African continent whenever the climate allowed it. “I don’t believe there was one big departure from Africa,” he said. “I think that throughout hundreds of thousands of years humans were coming in and out of Africa all the time.”

The discovery means that modern humans were potentially meeting and interacting during a longer period with other ancient human groups, providing more opportunity for cultural and biological exchanges. It also raises interesting questions about the fate of the earliest modern human pioneers. Genetic data from modern-day populations around the world strongly suggest that everyone outside Africa can trace their ancestors back to a group that left around 60,000 years ago. So, the inhabitants of the Misliya Cave are probably not the ancestors of anyone alive today, and scientists can only guess why their branch of the family tree came to an end.

【推荐3】You awake with a pounding heart and sweaty hands. Relax, you think to yourself — it was just a bad dream. But are nightmares truly benign(良性的)? Psychologists aren’t so sure. Although some continue to believe nightmares reduce psychological tensions by letting the brain act out its fears, recent research suggests that night ordeals (折磨) are more likely to increase anxiety in waking life.

In one study Australian researchers asked 624 high school students about their lives and nightmares during the past year and assessed their stress levels. It is well known that stressful experiences cause nightmares, but if nightmares serve to ease that tension, troubled sleepers should have an easier time coping with emotional ordeals. The study, published in the journal Dreaming, did not confirm that hypothesis (假设) : not only did nightmares not stave off anxiety, but people who reported being distressed about their dreams were even more likely to suffer from general anxiety than those who experienced an upsetting event such as the divorce of their parents.

It is possible, however, that something is going wrong in the brains of individuals who experience a lot of anxiety, so that normal emotional processing during dreaming fails, says Tore Nielsen, director of the Dream and Nightmare Laboratory at Sacred Heart Hospital in Montreal.

But Nielsen’s most recent results, published in the Journal of Sleep Research last June, actually bear out the Australian findings. To find out how REM sleep — during which most dreaming takes place — affects our emotions, the Canadian researchers showed horrible images(such as death scenes)to a group of healthy volunteers just before they went to bed. When the subjects viewed the same pictures in the morning, those who had been robbed of dream-filled REM sleep were less emotionally affected than those deprived of (剥夺) other sleep periods. The same was true for those who experienced fewer negative emotions in their dreams. In other words, having nightmares did not make dreamers more relieved in waking life — just the opposite.

What is not clear from these studies is whether nightmares play a causal role in anxiety. Most researchers agree that if the dreams give rise to constant anxiety and concern, it may be a good idea to talk to a mental health professional about it.