1 . Modern medicine’s ability to keep us alive makes it tempting to think human evolution may have stopped. But if we look at the rate of our DNA’s evolution, we can see that human evolution hasn’t stopped – it may even be happening faster than before.
Evolution is a gradual change to the DNA of a species over many generations. It can occur by natural selection, when certain traits created by genetic changes help an organism survive or reproduce. Such genes are thus more likely to be passed on to the next generation, so they increase in frequency in a population. Gradually, these changes and their associated traits become more common among the whole group.
By looking at global studies of our DNA, we can see evidence that natural selection has recently made changes and continues to do so. Though modern healthcare disrupts a key driving force of evolution by keeping some people alive longer, in countries without access to good healthcare, populations are continuing to evolve. Survivors of infectious disease outbreaks drive natural selection by giving their genetic resistance to offspring. Our DNA shows evidence for recent selection for resistance of killer diseases like Lassa fever and malaria. Selection in response to malaria remains in regions where the disease remains common.
Humans are also adapting to their environment. Gene change allowing humans to live at high altitudes have become more common in populations in Tibet, Ethiopia, and the Andes. The spread of genetic changes in Tibet is possibly the fastest evolutionary change in humans, occurring over the past 3,000 years. This rapid increase in frequency of a mutated gene that increases blood oxygen content gives locals a survival advantage in higher altitudes, resulting in more surviving children.
Diet is another source for adaptations. Studies show that natural selection favoring a change allowing adults to produce lactase – the enzyme (酶) that breaks down milk sugars – is why some groups of people can digest milk. Over 80 per cent of northwest Europeans can, but in parts of East Asia, where milk is much less commonly drunk, an inability to digest lactose is the norm. Like high altitude adaptation, selection to digest milk has evolved more than once in humans and may be the strongest kind of recent selection.
Yet, despite these changes, natural selection only affects about 8 per cent of our genome. But scientists can’t explain why some genes are evolving much faster than others. We measure the speed of gene evolution by comparing human DNA with that of other species. One fast-evolving gene is human accelerated region 1 (HAR1), which is needed during brain development. A random section of human DNA is on average more than 98 per cent identical to the chimp comparator, but HAR1 is so fast evolving that it’s only around 85 per cent similar. Though scientists can see these changes are happening – and how quickly – we still don’t fully understand why fast evolution happens to some genes but not others.
1. Which of the following statements may the author agree with?| A．Evolution occurs among several people overnight. |
| B．Genes may change and some are beneficial to people’s lives. |
| C．Evolution is done when the whole population possesses a certain gene. |
| D．The changed genes leading to higher survival rates are chosen deliberately. |
| A．explains | B．causes | C．upsets | D．heals |
| A．some people can resist infectious diseases like malaria |
| B．children in Tibet tolerate living environments with thin air |
| C．northwestern Europeans digest lactose better than East Asians |
| D．the human gene HAR1 resembles that of a chimp to a lesser extent |
| A．What Is Natural Selection? |
| B．Are Humans Still Evolving? |
| C．Why Will Certain Genes Evolve? |
| D．How Do Mutated Genes Function? |
2 . Facial expressions carry meaning that is determined by situations and relationships. For example, in American culture (文化) the smile is in general an expression of pleasure. Yet it also has other uses. A woman’s smile at a police officer does not carry the same meaning as the smile she gives to a young child. A smile may show love or politeness. It can also hide true feelings. It often causes confusion (困惑) across cultures. For example, many people in Russia consider smiling at strangers in public to be unusual and even improper. Yet many Americans smile freely at strangers in public places (although this is less common in big cities).Some Russians believe that Americans smile in the wrong places; some Americans believe that Russians don’t smile enough. In Southeast Asian cultures, a smile is frequently used to cover painful feelings. Vietnamese people may tell a sad story but end the story with a smile.
Our faces show emotions (情感), but we should not attempt to "read" people from another culture as we would "read" someone from our own culture. The fact that members of one culture do not express their emotions as openly as do members of another does not mean that they do not experience emotions.
Rather, there are cultural differences in the amount of facial expressions permitted. For example, in public and in formal situations many Japanese do not show their emotions as freely as Americans do. When with friends, Japanese and Americans seem to show their emotions similarly.
It is difficult to generalize about Americans and facial expressiveness because of personal and cultural differences in the United States. People from certain cultural backgrounds in the United States seem to be more facially expressive than others. The key is to try not to judge people whose ways of showing emotion are different. If we judge according to our own cultural habits, we may make the mistake of "reading" the other person incorrectly.
1. What does the smile usually mean in America?| A．Love. | B．Politeness. |
| C．Joy. | D．Thankfulness. |
| A．show friendliness to strangers |
| B．be used to hide true feelings |
| C．be used in the wrong places |
| D．show personal habits |
| A．Learn about their relations with others. |
| B．Understand their cultural backgrounds. |
| C．Find out about their past experience. |
| D．Figure out what they will do next. |
| A．Cultural Differences |
| B．Smiles and Relationship |
| C．Facial Expressiveness |
| D．Habits and Emotions |
