Yours,
Li Hua
Your letter reached me with pleasure.
Yours,
Li Hua
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? |
Notice
Apr. 20th, 2023
Students’ Union
I was given a voice. That’s what people said about me I trained my voice, because it would be a shame to waste such a gift. I pictured this voice as a greenhouse plant and made sure it was provided with the right temperature, the right amount of water. I relieved its fears. I told it not to tremble. I nursed it, I trained it, and I watched it climb up inside my neck
My voice bloomed. People said I had grown into my voice. Invitations to perform flooded over us. All the best places wanted us. I was sought after, or rather my voice was. We went everywhere together and gave performances. Bouquets （花束）were thrown to it. Money was presented to it. Men fell on their knees before it. Applause flew around it.
Then my voice began to shrivel. People said my voice would bloom only for a certain term: finally it would drop off and gone with it would be all the fame and wealth. I have noticed it so far. Fear has entered me since my voice has used up most of my life. I’ve given it all my love. But my voice is still as greedy as ever. It wants more: more and more, more of everything it has had so far.
Now it’s evening: the bright lights come on, and excitement quickens in the streets. We sit in this hotel room. Soon it will be time for us to go out. We have to attend a grand occasion. The two of us chained together as always. I have to put on its favourite dress, its favourite necklace and wind a fur around it. Then I have to go out: shining like ice: my voice attached to my throat like an invisible vampire （吸血鬼）.
1．Why did the author compare her voice to a greenhouse plant?| A．To introduce her way to grow a plant. |
| B．To stress her hard efforts to train her voice. |
| C．To express her determination to show her gift. |
| D．To indicate her strong desire to improve her skill. |
| A．go up | B．die away |
| C．grow more pleasant | D．become less attractive |
| A．The author totally ruined her fame. |
| B．The author gradually lost her freedom. |
| C．The author eventually accepted her voice. |
| D．The author greatly enjoyed her performances. |
A Mountain-climbing Activity
| A．is proved; where | B．proves; with which |
| C．proving; to which | D．prove; how |
“Ugh, chicken rolls again? I hate chicken rolls!” Matt yelled. “I’m not eating this.” Matt’s mom and dad looked at each other. Matt’s outbursts had been happening at least once a week all summer long.
“You know what, Matt? We re going to let you take over dinnertime from now on. You can pick the meals and cook them, as long as they’re healthy,” Mom said.
“Good, we’re going to eat good food every night!” Matt answered.
The next day, Dad sat down with Matt to make the meal plan so he could go grocery shopping. Matt had already been thinking about his favorite dinners. “We’re going to have beef tonight, and spaghetti tomorrow, and macaroni (通心粉) and cheese the next day,” Matt started.
“Woah, hold on now,” Dad said. “What else are we going to have with the beef? We need to have at least one vegetable with each meal, and usually we have another side to go with it.”
“Oh, yeah. Um, we can have corn with the beef,” Matt said.
“Sophia does not like corn,” said Dad.
“Well, it’s my choice, so I’m going to make corn,” Matt replied.
“OK, but she might complain at dinner tonight. Are you ready for that?” Dad asked.
“Yeah, whatever,” Matt answered.
Matt and his dad spent the next hour figuring out the whole week’s meals and side dishes. It was a lot more work than Matt expected, and almost every time he picked something out, his dad would tell him that someone in the family wouldn’t like it. It was very frustrating. “This is impossible!” Matt said.
“Yes, it is hard. Your mother and I try very hard to make everyone happy, but everyone has different tastes, and sometimes, we just can’t please everyone.”
“Fine, we’ll have to just go with this plan this week. Next week I’ll try to make everyone happy,” replied Matt.
When finishing grocery shopping, it was time for Matt to make his first meal.
Two hours had passed by before the dishes were ready on the table.
Molly ran back home from school and dropped her schoolbag on the sofa. Then on the table she saw “Mum’s Wish Book” —a mail order catalog from a gift shop. “Mum,” she said excitedly to herself, “this year you’ll get the gloves you want!” Molly had walked a dog for a neighbor and saved her money all year to buy Mum the gloves.
She opened “Mum’s Wish Book” and hoped that she could find these gloves in it. So carefully did she look through that tears ran down her face when she saw the gloves in the catalog. Mum wouldn’t buy them for herself, because the family had a hard time on the farm. She once heard Mum say to Dad, “Maybe some day, I’ll have the money to get them.”
Molly ran out by the back door and went straight to the post office. There she carefully filled out the order form torn from the catalog.
“I need to buy a stamp to send the form.” She said to Mr. Smith, the only worker in the post office.
“Umm, a pair of gloves?” said Mr. Smith, as he passed a stamp to her.
“Yes, It’s a Christmas gift for Mum, but please don’t tell her. It’s our secret, OK?” Molly didn’t realize how white Mr. Smith’s beard was until that moment. In fact, he reminded her of Santa Claus.
As Molly walked back home, she decided to tell Dad her secret. “You’ve got to check the mailbox every day,” said Molly quietly to Dad. He nodded, with a big smile.
Coming home from school every day, Molly peeked at Dad when Mum wasn’t looking , but every time he shook his head.
On Christmas Eve, Dad came back from the mailbox, still empty handed. Molly felt sad when she went to bed, because she didn’t have the gloves for Mum.
Before Christmas dinner, Molly felt so hopeless.
Mum thanked Mr. Smith and took the box .
| A．was damaged | B．were damaged | C．has been damaged | D．have been damaged |
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