What do Leonardo da Vincii, Marie Curie, and Albert Einstein have in common? They were all left-handed, along with other famous people including Brad Pitt Prince William, and Barack Obama. In fact, an estimated 13 percent of the world's population may be left-handed and still most people around the world are right-handed.

    What makes a person become right-handed rather than left-handed? As yet no one really knows for sure. One simple idea suggests that people normally get right-handedness from their parents. Studies have found that two right-handed parents have only a 9.5 percent chance of having a left-handed child, whereas two left-handed parents have a 26 percent chance of having a left-handed child. Another common theory is that left-handed people suffer mild brain damage during birth, which makes them left-handed. However, if this theory were true, it would not explain why the percentage of left-banded people is so similar in every society, when birth conditions vary so much from society to society.

    Whatever the reasons behind it, people's attitudes toward left-handedness have changed a lot over the years. Statistics show that although 13 percent of young people (10-20 years old) are left-handed, only 6 percent of the elderly are left-handed. Left-handed children used to be punished until they began using their right hand like other children, but today people who are left-handed are no longer looked down on nor are they considered abnormal. For most people today, either case is perfectly acceptable.

Dear Graham,

    My partner and I have recently lost a pet quite suddenly. Normal life is continuing with so much sadness for my pet meant so much to me. Lots of people won't understand my feeling this way about the death of an animal. This obviously isn't the first time someone in my life has passed away: when I was younger we lost elderly relatives who I loved very much, and naturally much-loved family pets died occasionally too. But this has hit me so much harder. I put so much love into the relationship and I'm just finding it hard to get my head around the fact that it's gone.

    Thank you for taking the time to read this.

ANON, VIA EMAIL

Dear Anon,

    Something you loved deeply has gone from your life, so of course you are sad. We love our pets differently from family members or friends and part of that is because we know they will probably die before us. Our time with our dogs or cats is precious precisely because we understand it is limited.

    As humans, we go through most of life understanding we would die one day. But animals don't. We are the keeper of the secret. Of course, living a life unencumbered(不受妨碍) by thoughts of death means that our pets, in general, lead very simple, happy lives. It's one of the reasons why they are such a joy to be round. You are, of course, correct when you say that many people don't understand your grief, so don't talk to them. Share your feelings with like-minded souls. I'm sure a simple search online will reveal many practical advice for moving on.

    And when you are ready, you can welcome another animal into your life and then you will enjoy happiness again.

GRAHAM, VIA EMAIL

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins “Twinkle, twinkle, little star” or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, additional learning experiences increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as “Twinkle, twinkle, little star” and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables (乘法口诀表) are an exception to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

    The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.

    Languages have been coming and going for thousands of years, but in recent times there has been less coming and a lot more going. When the world was still populated by hunter-gatherers, small, tightly knit(联系) groups developed their own patterns of speech, independent of each other. Some language experts believe that 10,000 years ago, when the world had just five to ten million people, they spoke perhaps 12,000 languages between them.

    Soon afterwards, many of those people started settling down to become farmers, and their languages too became more settled and fewer in number. In recent centuries, trade, industrialization, the development of the nation-state and the spread of universal compulsory education, especially globalization and better communications in the past few decades, all have caused many languages to disappear, and dominant languages such as English, Spanish and Chinese are increasingly taking over.

    At present, the world has about 6,800 languages. The distribution of these languages is hugely uneven. The general rule is that mild zones have fewer languages spoken by many people while hot, wet zones have more, often spoken by small numbers. Europe has only around 200 Languages: the Americas about 1,000, Africa 2,400; and Asia and the Pacific perhaps 3,200, of which New Guinea alone accounts for well over 800. The median number(中位数) of speakers is a mere 6,000, which means that half the world's languages are spoken by fewer people than that.

    Now over 400 of the total of 6,800 languages are close to extinction(消亡), with only a few elderly speakers left. None of these seems to have chances of survival.

    Next month, I'm traveling to a remote area of Central Africa and my aim is to know enough Lingala — one of the local languages — to have a conversation. I wasn't sure how I was going to manage this — until I discovered a way to learn all the vocabulary I'm going to need. Thanks to Memrise, the app I'm using, it feels just like a game.

    "People often stop learning things because they feel they're not making progress or because it all feels like too much hard work," says Ed Cooke, one of the people who created Memrise. "We're trying to create a form of learning experience that is fun and is something you'd want to do instead of watching TV."

    Memrise gives you a few new words to learn and these are "seeds" which you plant in your "greenhouse". When you practice the words, you "water your plants". When the app believes that you have really remembered a word, it moves the word to your "garden". And if you forget to log on (登录), the app sends you emails that remind you to "water your plants".

    The app uses two principles about learning. The first is that people remember things better when they link them to a picture in their mind. Memrise translates words into your own language, but it also encourages you to use "mems". For example, I memorized "motele", the Lingala word for "engine", using a mem I created — I imagined an old engine in a motel (汽车旅馆) room.

    The second principle is that we need to stop after studying words and then repeat them again later, leaving time between study sessions. Memrise helps you with this, because it's the kind of app you only use for five or ten minutes a day.

    I've learnt hundreds of Lingala words with Memrise. I know this won't make me a fluent speaker, but I hope I'll be able to do more than just smile when I meet people in Congo. Now, I need to go and water my Vocabulary!

    As I stuck in the mud (泥), with my bike on top of me, I wondered what had forced me to come here. Madagascar is not a good place for a cycling holiday: one of the world's poorest countries, only 11 percent of roadway is paved (铺). South of the town of Antalaha, where I started, the road was in worse condition.

    I appeared from a week in the wilderness and reached the start of the Route National 5 at Maroantsetra, but my dream of a smooth road and speed was suddenly destroyed by mud. The "worst road in the country" changed my bicycle into a burden (负担) for days. Finally, I was claimed by the road. Tired. Alone.

    As I wiped (擦) the mud from my face and looked upwards, I was greeted by a Malagasy man. He helped me stand up and smiled playfully while he pointed to my bike, which sat next to his. I started again. But I fell again in the mud. Angrily, I told him to go on, but if he understood he showed no sign of it. His smile forced me back onto the bike. We continued like this for hours. But I fell less. Studying my quick guide, slowly I learned. As we passed through a village, a group of children saw me and shouted loudly. His only words were: "Their parents tell them while people steal and eat them. Funny, no?"

    I tried to ask why, but he had already set off. I tried to catch up; as I got closer, he took it as a challenge and sped up. We raced along the road. I rode a little faster and I was just behind, about to catch up with him. With a smile, he sped up and was away, leaving me breathless.