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It has been more than 40 years since anyone has spotted a Japanese river otter. And the once common Yangtze River dolphins have either disappeared or are very rarely seen. These are just a few of the species that have been listed as extinct or locally extinct in recent years. But the advancement of technology could mean that the expunction of other species is not a given. 

A huge challenge scientists and conservationists encounter is tracking species facing extinction in order to help them. This is where artificial intelligence (AI) has brought about a revolution in the way data on these species is collected and analyzed. One example is the Maui dolphin, one of the rarest and most threatened dolphins in the ocean. Familiar with their summer. Behavior, researchers knew that there were just 54 of these elusive mammals living off the coast of New Zealand. However, because of weather conditions, researchers knew next to nothing about their winter behavior. After four years of developing, testing and fundraising, these scientists received permission to use a drone (无人机) with AI that tracked the dolphins no matter the season. The result was the extension of a marine sanctuary to protect their habitat. 

In parts of Australia, the koala was declared endangered in 2022 due to bushfires, habitat destruction and road accidents. Saving them was challenging because their whereabouts and numbers were relatively unknown. So Grant Hamilton, an associate professor of eco logy at Queensland University of Technology, began using drones with infrared imaging to locate them. An AI algorithm analyzes images to determine if a sighting is a koala. That information is then used to monitor and protect the species by restoring their habitats and providing health protection. 

In Zambia's Kafue National Park, home to 15 more than 6, 000 elephants, AI is being used to enhance traditional methods of preventing poaching. Cameras record any boats that try to enter the park on Lake Itezhi-Tezhi, an illegal entry point. Al immediately detects this activity and alerts park rangers, who deal with the illegal hunters.

The use of Al has helped to expedite action and increase conservationists' ability to protect the natural world for generations to come.

In an era led by texting and messaging apps, phone calls seem to be becoming a relic of the past, particularly among younger generations. A recent survey by Sky highlight s this shift, revealing that a quarter of 18–24-year-olds refuse to pick up the phone, and over half ignore calls from their parents. 

This raises the question: Why do we find phone calls so awkward, and is avoiding them damaging our relationships? The avoidance of phone calls isn't just a preference; it's a sign of worry. The immediacy and directness of a phone call, without the ability to carefully responses as in text-based communication, can be discouraging. This nervousness is not entirely new. Even traditional forms of speaking can cause it.

Phone conversations can be awkward due, to the lack of non-verbal cues. In face-to-face interactions, we rely heavily on gestures, facial expressions, and body language to interpret messages, which are absent in phone conversations. This can lead to misunderstandings and a feeling of disconnect. Additionally, the pressure to respond immediately without the buffer (缓冲) of time to think, as afforded by messaging apps, can increase the anxiety associated with phone calls. 

Despite the discomfort they may cause, phone conversations are an important skill. In the professional world, the ability to communicate effectively over the phone remains a critical skill. As I emphasise in my teachings and workshops, clear, confident, and authentic communication can significantly impact personal and professional success. . Therefore, it's crucial to teach younger generations, including Gen Z, the art of phone conversation, not just for professional success but also for fostering personal relationships.

Moreover, as I advocate in my approach to public speaking, incorporating emotional elements into communication enhances memorability and impact. Phone conversations, with their immediate and personal nature, can foster a deeper emotional connection than text-based communication. 

While it's understandable why phone calls can feel awkward in today's digital age, it's essential to recognize the value they hold in effective communication and relationship building.

As we guide this "phone anxiety pandemic (流行病)", it is crucial to encourage and relearn the art of phone conversation.

Steam trains paved the way for modern-day transportation, but just how much do you know about them?

The roots of steam trains can be traced back to the 18th century when the Scottish engineer James Watt improved steam engine technology. Watt's improvements significantly enhanced the efficiency of steam engines. This breakthrough paved the way for the application of steam power in various industries, marking the beginning of the Industrial Revolution. As the 19th century started, George Stephenson used the power of steam to power locomotives (火车头), telling the age of steam-powered transportation.

Steam trains played a vital role in transforming the world into a connected network of nations. The completion of the Transcontinental Railroad in the United States in 1869 marked a historic moment, as steam locomotives linked the East and West coasts, reducing travel time and expanding economic, opportunities. 

Similarly, the Orient Express in Europe became a symbol of luxury and international travel, carrying passengers from Paris to Istanbul in a quick way. The rhythmic sound of wheels on rails echoed (回响) through diverse landscapes, from the dry deserts of Australia to the snowy expanses of Siberia, as steam trains formed paths of connectivity across continents. During times of war, the role of steam trains extended to soldier transportation. 

While steam trains led the railway landscape for over a century, the mid-20th century witnessed the arrival of electric and diesel locomotives, claiming greater efficiency and lower operational costs, and signaling a transformative shift. 

As steam trains were not mainstream transportation, enthusiasts worldwide have preserved and restored steam locomotives, ensuring that these classic engine s continue to attract new generations with their nostalgic (怀旧的) charm, and that their stories continue to be told for ages to come. 

For Heritage railways, they dedicate to the restoration and operation of classic steam locomotives. From the Bluebell Railway in England to the Strasburg Rail Road in the United States, these living museums allow modern-day travelers to experience the magic of steam travel. Riding the polished carriages and hearing the distinctive whistle, visitors experience a sensory voyage, connecting with a time when steam trains were the heartbeat of progress and adventure. 

When you travel, do you like to dive into new adventures, or do you prefer to stay within your comfort zone? Undoubtedly, your unique personality helps determine what kind of trip you're most comfortable with.

Adventurous travelers

Perhaps you'd like to cage div e with sharks in Australia or jump out of an airplane in Dubai. Maybe you'd enjoy going on-a camel safari in India. Or you might like to river raft in Nepal. If these activities fill you with excitement and enthusiasm, you're probably an adventurous traveler.

Romantic travelers

Maybe your perfect vacation includes staying at an island beach house in Malawi and watching the setting sun's brilliant colors. Or perhaps you've dreamed of a leisurely walk along the Sein e admiring the iconic Eiffel Tower and seeing the lights of Paris. Does a trip to Italy's Amalfi Coast, with its splendid scenery and historical sites, appeal to you? If that's the case, you might be a romantic traveler.

Intellectual travelers

St. Augustine once said, "The world is a book and those who do not travel read only one page . . . "Many agree, and their goal of traveling. is to discover the mysteries, history and. culture within that "book. " They value spending time inside museums, at historical landmarks and visiting traditional cultural experiences.

Does that sound like you? If so, you may be an intellectual traveler. 

First-time travelers

If you've never traveled internationally, you fall into this category. Many first-time travelers worry about how to communicate, how to get around and more. For your first trip outside your country, pick somewhere with a familiar culture. You'll experience less culture shock if the food, language and other things seem somewhat familiar. .

After spending Thanksgiving on Uncle Howard's farm, he gave us two turkey eggs. My younger brother Chris was so excited that he nearly dropped his egg on the way home. Dad put the eggs under an old hen in our backyard. Every day Chris and I would check to see if they'd hatched yet. 26 days later, two little creatures waddled (摇摇摆摆地走) behind the hen. As they got older, one was dead. We named the other Timothy.

Timothy liked to wander in the woods and find tasty berries and weed seeds. Mom kept telling us not to get too attached to Timothy, because we were going to have him for Thanksgiving. But we never paid too much attention to what that really meant. One day, Dad gave Chris and me instructions. "I want you to start giving him corn along with his regular feed, " he said. "We want a nice fat bird for Thanksgiving. " After Dad walked away, Chris's face began to pucker, just as he did before he started to cry.

"Don't worry, Chris, " I said comfortingly. "We'll save Timothy, somehow. "

"Why don't we give him away?" Chris suggested.

"No. " I said. "If we do, he'll just end up on someone else's Thanksgiving table. " Suddenly I had an idea. "Hey, Chris, you know that small cave in the woods?" Chris nodded. "We can take Timothy there. We'll cover the entrance with a wire net and hide him till Thanksgiving is over. " "Yeah!" We were so excited that we gave each other high-fives. We took Timothy out of his cage and left him in the cave with water and plenty of food. We piled branches over the opening to hide the entrance.

One day Dad sent us out to look for him. Both of us felt guilty but we wanted to save Timothy's life, so we kept quiet. Finally, Dad decided that a fox must have gotten him. That year Uncle Howard provided a turkey for our Thanksgiving dinner. The next day a big snowstorm hit. It was days before we could get out and see Timothy. When we got to the cave, we saw something had happened.

注意：1. 续写词数应为150左右；2. 请按如下格式在答题卡的相应位置作答。

The wire net was pulled away from the entrance, and Timothy was gone.

"Look at that！It's Timothy！"Mom cried one day.

注意：1. 写作词数应为80左右；2. 可以适当增加细节，以使行文连贯；3. 请在答题卡的相应位置作答。

A dragon dance performance featured the Mulberry Leaf Dragon (桑叶舞龙) from Deqing county and the Bamboo Leaf Dragon from Anji county, both in Zhejiang province, which were  (impressive) showcased at Hangzhou Olympic Sports Centre Stadium as part of the warm-up festivities for the opening ceremony of the 4th Asian Para Games. 

As  cultural heritage in Zhejiang, the Mulberry Leaf Dragon has become a significant representation of local folk culture. 

Tang Yongming, the deputy secretary of the village Party committee,  (explain) that this dragon was 22 meters in  (long) with a total of 11 parts. Its body was woven from bamboo strips, and it (name) so because the scales were shaped like mulberry leaves. The members of the team were all local villagers  had been learning the dragon dance since childhood. 

The program Dragon Soars in the Bamboo Sea (present) by Anji county is also one of the provincial-level intangible cultural heritages. It involved thirty-five performers disabilities from the county's Disabled People's Federation Art Troupe.

The performance was based on Anji's bamboo culture and the Bamboo Leaf Dragon, including over 20 bamboo musical (instrument), such as pipe organs, flutes and drums. The team's instructor, Gan Huifen, said, "All prepared diligently, rehearsing for over three months, and making efforts (deliver) their best performance. "

Brady has been diagnosed with terminal cancer. It has been 1  for his family and his students. He was 2  not only because he was a rising star, but also because he had recently 3  the highest honors for young researchers at the White House. 

We truly 4 him — as someone put it, "He always has a smile and a kind word for everyone. " It is very 5 to find someone who is extremely intelligent should be so nice.

Last week, I bought a simple card, reading, "Healing thoughts and wishes are coming your way. We are all 6 for your recovery". I met and made all his students, who have worked pretty closely with him, sign and add a 7 on it.

He is still undergoing intense treatment, trying his best to stay 8 and hopeful. He didn't show any trace of self-pity or sadness when I met him. 9 , he paid attention to every word of my presentation and asked me several questions 10 to my work, though being in great 11 . I saw an expression of joy and hope on his face as he opened the card. He said he was 12 to see the messages from the students. Then he 13 , "I am trying to focus on staying positive, hoping to be back this summer. "

Despite being too sick to teach classes, my professor has managed to continue being a great teacher, introducing his last 14  messages to us. It is so important to tell people how much they 15  to us before it is too late. 

A study reveals it's beneficial to write about a painful experience or difficult situation in a way that psychologists refer to as "expressive writing".

Expressive writing is a specific strategy different from keeping a journal. The idea is to reflect honestly and thoughtfully on a particular suffering or challenge. Hundreds of studies have found that it can strengthen the immune system, including for people with illnesses such as depression, cancer, and PTSD.  And it may even help reduce symptoms of depression and PTSD, and prevent colds and flu. 

 Translating that disturbance into language forces you to organize your thoughts. Additionally, creating a story offers you a sense of control. Expressive writing works because it allows you to make meaning out of a painful experience. 

Talking about an event can lead to reflection, where you are lost in emotions and may become overexcited. But writing forces you to slow down. Writing can reduce the neural activity in the brain, leading to a positive mood and an enhanced appreciation for life. 

What if you think you're not expert at writing? Do dig deep into your thoughts and feelings. The goal of writing is to find meaning in an upsetting event. When you acknowledge the pain, you will be able to see the courage to face fears.

But there are a few warnings. People coping with a severe pain or depression may not find it useful to do alone without therapy. It shouldn't be used as a replacement for other treatments. Yet it can be a powerful coping tool for many, because it helps people fight the fear to face emotions.

A. It can relieve pain and improve mood. 

B. Don't worry about spelling or grammar.

C. Expressive writing isn't a magical cure for all.

D. Expressive writing is a recording of what happens. 

E. Spend just a few minutes taking down your feelings. 

F. Realizing what is disturbing you is an important first step. 

G. Writing increases one's acceptance of experiences, and acceptance is calming.

In the summer of 2021, an unseasonal event took place. More than 100 miles of Florida's coast around Tampa Bay became an oxygen-depleted (缺氧的) zone containing dead fish along the nearby shoreline.

Much of the conversation around our climate crisis highlights the emission of greenhouse gases and their effect on warming, sea-level rise and ocean acidification (海洋酸化). We hear little about the effect of climate change on oxygen levels, particularly in oceans and lakes. But water without adequate oxygen cannot support life. For the three billion people who depend on coastal fisheries for income, declining ocean oxygen levels are devastating. 

As ocean and atmospheric scientists focus on climate, we believe that oceanic oxygen levels are the next big victim of global warming. To stop the situation from worsening, we need to expand our attention to include the dangerous state of oceanic oxygen levels — the life-support system of our planet. We need to accelerate ocean-based climate solutions that boost oxygen. Examples include nature-based solutions such as those discussed at the 2021 United Nations Climate Change Conference (COP26) held in Glasgow. 

Enhanced monitoring of oxygen and the establishment of an oxygen-accounting system are a must. Putting oxygen into the climate story motivates us to do the work to understand the deep systemic changes happening in our complex atmospheric and oceanic systems. We celebrated the return of humpback whales in recent years to an increasingly clean New York Harbor and Hudson River. However dead fish blocked the Hudson in the summer as warmer waters carried less oxygen. 

Ecosystem changes connected to physical and chemical system-level data may point the way to new approaches to climate solutions. It includes an enhanced understanding of the life-support system of our planet. Roughly 40 percent of the world's people depend on the ocean for their livelihoods. If we do not save marine life from oxygen starvation, we starve ourselves.

Night owls may be prone to heart disease and diabetes (糖尿病) than early birds because their bodies are less able to burn fat for energy, U. S. researchers say. People who rise early rely more on fat as an energy source. They are often more active in the day than those who stay up later, meaning fat may build up more easily in night owls, the scientists found. 

The findings may help explain why night owls are at greater risk of type 2 diabetes and cardiovascular disease. They may also help doctors to identify patients early on who are more likely to develop the conditions. 

The researchers divided 51 fat middle-aged adults into early birds and night owls, depending on their answers to a questionnaire on sleeping and activity habits. They monitored the volunteers' activity pattern for a week and tested their bodies' fuel preference at rest and while performing moderate or high-intensity exercise on a treadmill.

In Experimental Physiology, the team described how early birds were more sensitive to blood levels of the hormone insulin (胰岛素) and burned more fat than night owls while at rest and during exercise. The night owls were less sensitive to insulin and their bodies favored carbohydrates over fat as an energy source. 

Prof Steven Malin, a senior author on the study and an expert in metabolism, said it was unclear why differences in metabolism were seen in night owls and early birds. But one possibility, he believes, is a mismatch between the time people go to bed and wake the next morning and the circadian rhythms (昼夜节奏) that govern their body clocks. 

The findings could affect discussions around the health risks of night-shift work and even changing the clocks to suit daylight hours. "If we promote a timing pattern that is out of sync with nature, it could worsen health risks, " Malin said. "Whether dietary patterns or activity can help reduce these is an area we hope becomes clear in time. "

When I was a girl of eight, living in a town, I used to work for Mrs. White, an elderly lady. She paid me very little for my work, because she didn't have much money. She did, however, promise to give me a Christmas present. The girls I played with had baseball gloves, bicycles and ice skates, and I was so eager to acquire any one of these. On Christmas morning, Mrs. White gave me a little package which could hardly hold anything. I was painfully disappointed but she told me it was a kind of magic. My disappointment turned into curiosity.

With great excitement I opened the package, only to find a pile of ten sheets of black paper inside, each labeled in colorful letters, Carbon Paper Regal Premium. I didn't know what it was. "Is it magic?" I asked. My Aunt Karen, who was a school teacher, answered, "It really is!" She took two pieces of white paper and placed between them one of the black sheets from the box. Then, with a hard pencil, she wrote my name on the upper sheet. Removing it and the Carbon Paper Regal Premium, she handed me the second sheet, which her pencil had in no way touched. There was my name!

I was enthralled. I wrote and wrote, using up whole tablets until the last piece of black paper was used up. It was a game I didn't want to end. I was very happy with my special gift. I can honestly say that, in that one moment, I understood as much about printing, copying words and the mystery of spreading ideas as I have learned in the remaining half-century of my life.

I hope that this year some boys and girls will receive, from thoughtful adults who really love them, gifts that will shock them. It is such gifts and such experiences — usually costing little or nothing — that transform a life and lend it a motivation that may continue for decades. 

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This is the most popular e-book which centers around how to keep one's figure using traditional weight loss methods. The new edition includes two cover stories: Why Your Brain Needs Exercise, which looks at the benefits of exercise in an evolutionary context, and Obesity on the Brain, which examines the effects of unhealthy foods on the brain.

On-Sale Date: January 1, 2023

Price: $7. 66

Mysteries of the Mind

For more than a century, scientists have investigated the workings of nature's most complex organ — the brain. Findings are moving us closer to understanding processes such as how we make decisions. In this e-book, we examine the latest research on how we can improve mental health.

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The Mystery of Sleep

The reason we need sleep has long puzzled scientists, but it's clear that we do need it. In fact, the more we learn about what happens while we sleep, the more we discover new benefits for multiple processes including hormone balance, emotional health, learning and memory. Studies show that even one night of disturbed rest can lead to measurable harm, and for this mini-collection, we've gathered the most recent research on sleep.

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The Science Behind the Debates

People say that they trust scientists, yet evidence often takes a back seat to emotions. In fact, for issues that cause the most public anger — like vaccine safety — there is almost no debate in the scientific community. In this e-book, we examine the science behind today's most arguable debates including GMOs (转基因生物) and evolution, as well as strategies for understanding and coping with denialism (否定主义).

On-Sale Date: March 4, 2022

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Once upon a time, in the midst of a fine summer, Tom and his younger brother Jack went on an amazing trip to a picturesque beach with their family. 

Excitement filled the air as Tom and Jack eagerly packed their buckets and shovels (铲子), ready to explore the sandy wonders that awaited them. The moment they arrived at the beach, they wasted no time and rushed directly towards the shoreline. 

With the wind brushing gently over their cheeks, Tom and Jack dug their hands into the soft grains of sand, laughing happily as they felt grains of sand passing through their fingers. Their laughter was echoing along the coast. 

Then the two little brothers decided to build a splendid sand castle that would leave everyone in awe. With the sound of seabirds singing in the background, they began their grand project. Side by side, they cupped their hands, dug into the soft beach, and started building their dream castle. With great care and precision, they sculpted and shaped the sand with their fingers, crafting each tower and wall. The boys were lost in their work, feeling the warmth of the sand beneath their fingers. They seemed to hear whispering tales of the distant, mysterious ocean. 

Time seemed to stand still as the boys poured their hearts into every detail of their sandy creation. With each passing moment, the sand castle grew in both size and beauty and it began to take shape. Together, they patiently decorated their dream castle with seashells and twigs, imagining a world of soldiers, princesses, and magical creatures. 

Seeing the castle stand proudly before them, the two little brothers breathed out a sigh of relief. Their eyes shone with excitement. They were like architects who were appreciating their masterpiece that expressed their extraordinary imagination. 

注意：1. 续写词数应为150左右；2. 请按如下格式在答题卡的相应位置作答。

However, just before they knew it, the seawater began to rise. 

Jack nodded his head in agreement and they determined to rebuild it 

注意：1. 写作词数应为80左右；2. 请按如下格式在答题卡的相应位置作答。

Dear Caroline, 

Yours sincerely, 

Li Hua

Doing morning exercises is a daily routine in every Chinese kindergarten and school. For the grown-ups, however, familiar schoolyards have already been replaced  public parks. 

The morning scenes in central parks around China are lively. At every corner of the park, you can also see people  (practise) many kinds of sports: square dancing, badminton and so on. 

But the most eye-catching groups in the park are the so-called "Kung Fu Grandpas/ Grannies", videos have gone viral on the Internet. Most of them are ordinary workers from different industries who only started working out after their (retire). They say age is just a number when it comes to fitness.

The  (benefit) of exercise are endless: a healthier body together with a slimmer figure and a  (happy) mood. No matter how old they are or when during the day they exercise, they will always strengthen the body. 

Social connection is also  the elderly seek during their morning workout. Feng, who is seventy-two years old, plays Taichi every day. He  (keep) this exercise routine for six years and now he is managing a WeChat group of 270 members who share  same hobby. 

"What I like about this place is that newcomers are always welcome. Everyone in the park feels (include), " said Feng. It is like a chorus of life.

Elmer Whitaker sighed as he looked over his muddy crops. A terrible 1  had swept through his farm the night before, and his crops were now covered in 2  and destroyed. His neighbor, a kind young man named Thomas, 3  to offer his help. 

"What a disaster, "Whitaker said. " My whole family has always survived on the harvests of this field. I feel 4 and don't know what to do now.

Thomas calmed him down and thought for a moment. "I see this not as a disaster but as an 5 , " he said. Whitaker looked at him 6 . "How can it be?" he asked. Thomas smiled 7 , "Now you have a chance to try something new. You've always grown beans and cabbages. Why not try planting 8 crops that will also fit in this soil? You can diversify and therefore 9 your farm once again. "

Elmer Whitaker considered this. Thomas was right-he had become set in his ways. This disaster could push him to make his farm 10 and sustainable in a new way. "You have 11 me, " Whitaker said. He clapped Thomas on the back. "Thank you for showing me the opportunity in this difficulty. "

And so Whitaker 12 new crops and soon, the farm was full of life again. Farmers from neighboring towns were 13 with the wonder of Whitaker's fields, and they began to 14 their crops as well. Elmer Whitaker's farm has become a 15 of adaptability and hope, telling everyone that in every storm, there is a chance for new growth.

If you are seeking a job, you need to pay attention to your social media and online comments.  The following reminders may help you use social media well and grow your career. 

∙ Choose online platforms wisely. 

Instead, decide on one specific platform where you know what to expect and where you can feel safe and supported, and then build your personal channel there. It's often where people look first to find out more about you. Make it as a space to show the best reflection of you and a place to tell your story and how you want it to be told.

∙ 

Know that people are watching-and it is not just your followers. Your potential clients and employers are paying attention, too. They want to learn about you and see if you are a good fit. The key is defining your professional image. Understand how you want to present yourself to the world, show what you want to be known for, and impress them with your best image. 

∙ Keep it clean and legal. 

This is not to limit free speech but to set rules for a respectful, professional environment. Besides, knowing and understanding the basics of copyright law can help. For example, photos are protected by copyright from the moment they are taken, whether they are registered or not. It is OK to share online videos and photos with your friends, without asking for the owner's permission and without paying fines.

If you use social media to your advantage, jobs will flow your way, not away. It's all in your hands.

A. Befriend your future colleagues. 

B. Define your own personal image. 

C. You don't have to register every online platform.

D. Consider setting ground rules for your online channel. 

E. Anything that has ever been shared on the Internet is rediscoverable. 

F. However, using them in your social media is against the copyright law. 

G. They are open for any and all to see-including your future employers. 

One of the biggest challenges that traditional educators face is how to unlock students' love of learning. Once students overcome their fear or unwillingness, they will be on the track of becoming motivated learners.

In order to help students discover the joy in learning, some teachers are turning to a simple but effective strategy called gamification-using game-related elements such as activities and rewards to promote students' engagement in class. With an origin in educational psychology, this approach is designed to reach students by making the learning process funny and interesting.

What's more researches show that gamification can also make assignments less stressful. Without too much pressure, students will associate learning with curiosity and joy. Accordingly, they feel like continuing the journey because positive feelings have boosted their confidence.

But like any other strategies, gamification has its drawbacks when used incorrectly. It is very likely that some students only focus on winning rewards but have no interest in understanding concepts or learning new skills-exactly the opposite of the desired outcome. To avoid this, teachers can help prevent students from becoming wrongly motivated by choosing suitable rewards. Instead of class parties or snacks, try rewards that help students develop a passion for academic subjects. 

For example, have students earn points towards a class field trip by behaving and doing their assignments, or pair subjects that a student dislikes with fun books or activities to encourage motivation. That way, they associate fun with reading, math, or other skills. More examples include competing on a leader-board, holding a talent show, or playing other team-building games. All activities and rewards need to be carefully selected and well arranged. 

If you're having a hard time getting your class interested in learning, talk with them together or individually about what motivates them and include it into your student engagement strategies.

If "Why?" is the first question in science, "Why not?" must be the second one. It's interesting to think about why something does not exist in nature, such as a three-legged animal.

In an online lecture, David Jackson, a biologist in Earth and Planetary Sciences, was challenged to come up with "an animal or plant that does not and cannot exist". Jackson told the audience that in nature, no species known to date has ever been born with a third leg.

Jackson pointed out that, however, many animals do use a particular three-legged pose for support. Examples include meerkats (猫鼬) resting on their tail and back feet and woodpeckers (啄木鸟) using tail feathers to weigh themselves against a tree trunk, which is more stable and requires less energy. Given that three-legged movement does work in some situations, why are there no animals with three legs?

The answer may be at the core of evolution. Over a long time in history, almost all animals have adapted themselves and developed into a body shape which is organized around a central point and can be divided into two similar halves. Butterflies are an excellent example. Not only can their body shape be divided into two matching halves, but also the patterns on each wing are exactly the same. The law of having two sides to everything has been in our DNA since the first animals appeared on the earth. 

And it is important to remember that only those biological changes that prove to have brought advantages can be passed down to next generations. If there were three-legged animals, there would be some good reasons for that to happen. However, three-legged animals would not be able to run as fast as four-legged animals. And they would also not be as efficient as two-legged animals. Three legs would simply make climbing, walking, running, and sleeping more difficult. 

"The non-existence of three-legged animals can also be seen as the result of natural selection, " Jackson explained to the curious audience.