If we were asked exactly what we were doing a year ago，we should probably have to say that we could not remember. But if we had kept a book and had written in it an account of what we did each day, we should be able to give an answer to the question．

    It 1s the same in history．Many things have been forgotten because we do not have any written account of them. Sometimes men did keep a record of the most important happenings in their country, but often it was destroyed by fire or in a war．Sometimes there was never any written record at all because the people of that time and place did not know how to write．For example，we know a good deal about the people who lived in China 4,000 years ago，because they could write and leave written records for those who lived after them．But we know almost nothing about the people who lived even 200 years ago in Central Africa，because they had not learned to write．

    Sometimes，of coures，even if the people cannot write，they may know something of the past．They have heard about it from older people，and often songs, dances and stories have been made about the most important happenings, and these have been sung，acted and told for many generations，for most people are proud to tell what their fathers did in the past．This we may call”remembered history”．Some of it had been written down. It is not so exact or so valuable to us as written history is，because words are much more easily changed when used again and again in speech than when copied in writing．But where there are no written records，such spoken stories are often very helpful．

    NOT all memories are sweet. Some people spend all their lives trying to forget bad experiences. Violence and traffic accidents can leave people with terrible physical and emotional scars. Often they relive(再体验)these experiences in nightmares.

    Now American researchers think they are close to developing a pill, which will help people forget bad memories. The pill is designed to be taken immediately after a frightening experience. They hope it might reduce, or possibly erase(抹去), the effect of painful memories.

    In November, experts tested a drug on people in the US and France. The drug stops the body releasing(释放)chemicals that fix memories in the brain. So far the research has suggested that only the emotional effects of memories may be reduced, not that the memories are erased.

    The research has caused a great deal of argument. Some think it is a bad idea, while others support it.

    Supporters say it could lead to pills that prevent or treat soldiers' troubling memories after war. They say that there are many people who suffer from terrible memories.

    "Some memories can ruin people's lives. They come back to you when you don't want to have them in a daydream or nightmare. They usually come with very painful emotions," said Roger Pitman, a professor at Harvard Medical School. "This could reduce lot of that suffering."

    But those who are against the research say that changing memories is very dangerous because memories give us our identity(特质). They also help us all avoid the mistakes of the past.

    " All of us can think of bad events in our lives that were horrible at the time but make us who we are. I'm not sure we want to wipe those memories out," said Rebecca Dresser, a medical expert.

    Are you sick of going to bed late and waking up tired? Then grab your hiking boots and a tent. A new study suggests that camping in the great outdoors for a couple of days can reset your body clock and help you get more sleep.

    The body clock is an internal system that tells our bodies when it's time to go to sleep and when it's time to wake up. Scientists track this clock by measuring the amount of melatonin (褪黑激素) circulating in a person's blood at any given time.

    In a healthy sleeper, melatonin levels rise a few hours before bedtime, stay high through the night, and then settle back down when it's time to wake up.

    In our modern society, however, most of us stay up many hours past sunset and would probably sleep in many hours after sunrise if we could. And the trouble is, your melatonin levels may still be high when your alarm clock goes off in the morning, which leads to fatigue. It may also have other health consequences as well, such as diabetes (糖尿病), overweight and heart disease.

    Professor Kenneth Wright of the University of Colorado in the US wanted to see if our body clocks can be reset by a short stay in nature. His team recruited (招募) fourteen physically active volunteers in their 20s and 30s. Nine went on a weekend camping trip, while the other five stayed home. At the end of the weekend, the researchers reported that in just two days, the campers' body clocks had shifted so that their melatonin levels began to rise more than an hour earlier than they did before they left on the trip. By contrast, the body clocks of the group that stayed home shifted even later over the course of the weekend.

    “This tells us we can reset our clocks fast,” Wright said.

    Therefore, if you want to change your sleep patterns you could try to increase your exposure to natural light during the day and decrease the amount of artificial light you see at night. And if that doesn't work，there's always camping.

    On a cool morning, Wilson Kasaine heads out along a dirt path in southern Kenya. His calmness makes it easy to forget that he's tracking one of the most dangerous animals in the world. Kasaine is tracking lions—especially one lion called Marti, who is the real-life Lion King of Selenkay Conservancy.

    Tracking lions on foot may sound like a death wish, but Kasaine has been doing it for most of his life. Born into a traditional Maasai family he quickly grew to understand the beauty and danger of wildlife. Living with big wild animals forces him to develop a good sense of where they have been and where they may be going. During his 12-kilometer walks to and from school, he learned how to tell the paw prints (爪印)of a lion from those of other animals.

    Growing up, Kasaine knew that improving his tracking abilities would help him avoid surprise meetings with dangerous animals. For many Maasai, tracking is mainly a matter of self-protection. But Kasaine is tracking lions to meet them and to protect them. He leads a small group of wide-eyed tourists over the red sandy path, searching for the lion that has left upon it his prints.

    Each year, thousands of tourists crowd Kenya's national parks to try to have a look at the “big five”; elephants, rhinoceros, leopards, buffaloes and lions. The international draw of these animals matters a lot because the nation's economy is tied to the protection of its wildlife. If Kenya's wildlife disappears, so does its second-largest source of income.

    Wildlife protection efforts in Kenya meant marking off land exclusively (专门地) for animals. But it also meant that the people who had originally lived in the area were forced to leave their land and into smaller surrounding areas. They are also finding it increasingly hard to keep a traditional Maasai lifestyle. But people are glad that it really makes a difference to wildlife protection.

    Darwin noted that some human emotional expressions might have started as part of a physiological function: for example, exposing the teeth to bite food. The function, however, took on meaning and became a form of communication which signals anger.

    The same may be true for the animals. Baby monkeys cry for attention. They also cry to signal to an adult that they want to be carried.

    “Chimpanzees do make upset voice when they are being weaned (断奶) by their mothers or have lost their mothers or another individual,” says Anne Pusey, a professor at the University of Minnesota. “They whimper (呜咽) and cry and scream. When we hear these calls, the emotion involved seems obvious. However, they do not weep in the sense of producing tears. I have seen an adolescent male whimpering when he lost sight of his older brother with whom he had been traveling.”

    Babies of many mammalian species, including rats, cry. Moreover, when a baby rat cries, often his mother brings the fallen pup back into the nest. This is probably a straightforward communication, as it is with humans. However, psychologists at the University of Iowa aren't convinced.

    The Iowan researchers can cause the same crying sounds by producing large decreases and then increases in blood flow. The blood flow also goes down when baby rats get cold. Thus, they conclude baby rats cry in the same way that we sneeze. Of course the rat baby could be crying because he's cold and wants his mother to know.

    “All young mammals make cries when separated from their mother,” says Jaak Panksepp, a psychologist at Bowling Green State University. “If you're willing to call this crying, then certainly other animals show this emotional response.” he says, “Some of us take seriously that animals do have emotions.”

    Hundreds of children are being treated for sleep problems in Wales every year. In some cases, babies, infants and teenagers have been admitted to hospital while in north Wales alone.

    The Children's Sleep Charity said many children were suffering from lack of sleep mainly because of technology use. Public Health Wales said sleep was as important to a child's health as healthy eating and exercise, and children with poor sleep patterns were more likely to be fat.

    Statistics obtained under the Freedom of Information Act by BBC Wales found at least 408 children have been admitted to hospitals across Wales suffering from sleep disorders since March 2013.

    Children aged between 0 and4 made up the highest number of inpatients (住院病人), with some newborns being treated for sleep-related problems from the day of birth.

    Vicki Dawson, who set up the Children's Sleep Charity (CSC), said sleepless nights were putting both children and parents in anxiety. "Their weight and growth may also be affected as well as their mental health," she said.

    Teachers said children showing signs of sleep shortage and tiredness in class were a concern as they couldn't concentrate for long periods.

    Psychologist Amy McClelland, of Sleep Wales, said a common problem was children being "over excited" and "not having the chance to relax property" before bed and families should get back to basics. "Think 1950s family home. Dinner as a family, read, chat, a film maybe, lights off and then bed." She added.