【推荐1】A new study suggests that identical twins are not exactly the same genetically. Identical twins are two babies that come from the same fertilized egg (受精卵). Scientists in Iceland examined DNA from 387 pairs of identical twins, their parents, children, husbands or wives. “The examinations led the team to find early mutations (突变) that separate identical twins,” lead researcher and geneticist Kari Stefansson said. He is a professor at the University of Iceland and founder of the company deCODE genetics.

Mutations are small changes in DNA that can happen when a cell divides in an attempt to copy itself. These small changes can influence a person’s physical appearance or control a person’s ability to fight a disease. The newly-discovered mutations show that identical twins do have genetic differences, the researchers said. The results were recently published in Nature Genetics.

On average, identical twins have 5.2 of these early genetic differences, the researchers found. But about 15 percent of identical twin pairs have more than that. Some may have as many as 100 genetic differences, Stefansson said. These differences represent a small part of each twin’s genetic material. But they could influence why one twin is taller or why one is at greater risk of some cancers than the other.

In the past, many researchers believed physical differences seen in identical twins were related mostly to environmental influences, such as nutrition or lifestyle behaviors. Jan Dumanski is a geneticist at Sweden’s Uppsala University. He was not involved in the study. He praised the findings as a clear and important contribution to medical research. “It suggests we have to be very careful when we are using twins as a model for examining the influences of genetics or the environment,” Dumanski said.

A 2008 paper in The American Journal of Human Genetics found some genetic differences between identical twins. The new study, however, goes beyond earlier work by including the DNA of parents, children, husbands and wives of identical twins. Studying family members permitted the researchers to examine when genetic mutations happened in two different kinds of cells: those present in only one individual and those passed on to the person’s children.

Stefansson said his team found twins where a mutation is present in all cells of the body of one twin, but not in the other twin at all. “However, sometimes the second twin may show the mutation in some cells, but not all cells,” he added. The researchers said they also found mutations that came about before the developing embryo (胚胎) split in two.

Nancy Segal is a psychologist who studies twins at California State University, Fullerton. She was not involved in the study. But she called the result “heroic and really significant”. Segal added that the research is likely to persuade more scientists to rethink the influences of genetics and environment on twins. “Twins are very alike, but it is not a perfect similarity,” she said.

【推荐1】A short while ago, I lost access to my We Chat account.I am not sure why it wouldn’t let me log in; perhaps it was my ancient, out-of-date phone. But I wasn’t upset because it offered me an opportunity to take a break from social media-something more and more people are doing.

In the United States, Twitter and Facebook has seen a 44 percent decline among its younger users. Stars such as Taylor Swift and Ed Sheeren have taken a break from social media because they were tired of so many Internet trolls leaving negative comments. Ordinary people (like me) are turning away from it because of the feeling that they were spending more time online and enjoying less.

It is not unusual for people to spend two or three hours a day posting or reading posts, to the point where it becomes an addiction.And it is an addiction. There is a chemical in your brain known as dopamine (多巴胺) which is sometimes called the “reward molecule”and its release gives you a feeling of pleasure. For instance, when you post a photo on We Chat and get a hundred likes, you feel happy. That’s dopamine at work.

In my case, being off We Chat is actually an added bonus. No doubt I missed my dopamine. And I got e-mails from friends wondering if I was fine or if I was just being anti-social. But I soon began to feel quite peaceful and started to worry less about what other people were doing and concentrate more on my personal life. And I’m getting better sleep at night.

I’m not advocating that all of you quit social media, but spending less time on these platforms does bring you advantages.

【推荐2】The Internet has become part of teenage life. There’s a report on 3375 students aged from 10 to18 in seven Chinese cities. It says that 38% of them believe they use the Internet often. While most of them get useful information and use the Internet to help in their studies, some are not using it in a good way. Many are playing online games too much. A few even visit Websites they should not look at. Bad things can happen if young people spend too much time on the Internet.

In order to help young people use the Internet in a good way, a textbook on good Internet behavior has started to be used in some Shanghai middle schools this term. It uses real examples to teach students all about good ways of using the Internet. Some students also make online friends. But if you are meeting a friend offline, let your parents know.

Teachers and parents all think the book is a very good idea. It will teach students how to be a good person in the online world. It will be a guide for teens using the Internet and keep students away from bad sites.