古时保护人类的基因可能与现代疾病有关

胡静

Scientists have compiled the largest database of ancient DNA based on the bones and teeth of almost 5，000 humans who lived across Western Europe and parts of Central Asia from 34，000 years ago until medieval times.

Analysis of this uniquely detailed pool of ancient genetic information suggests genes that may have once protected prehistoric hunter-gatherers or Bronze Age herders from harmful pathogens（病菌） may today increase the risk of neurodegenerative diseases such as multiple sclerosis and Alzheimer’s in Europeans.

By comparing the ancient DNA with modern-day samples， the researchers gained a new biological understanding of debilitating（衰弱的） disorders and physical traits in the present day.

One of the key findings from the first batch of research was connected to MS. It’s a complex condition shaped by multiple environmental and genetic factors with many potential symptoms. Northern Europeans are among those most prone to the the disease， the study noted， but the reasons why are little understood. By using the database， researchers found that genetic risk of having the condition correlates to the proportion of ancestry（血统） from a group of ancient pastoralists.

These nomadic（游牧的） herders， known as the Yamnaya， originated from the Pontic steppe. It’s thought they were the first horse riders， making them highly mobile. They brought specific genetic variants when they moved westward into Europe， these genetic variants may be beneficial to European populations in making the shift from hunting and gathering to farming.

The team concluded that the increased proportion of pastoralist ancestry in present-day northern Europeans might be partly responsible for the higher prevalence（流行） of the disease there.

Today， the protective benefits of these genetic variants are no longer as useful. We now lead very different lives to those of our ancestors in terms of hygiene， diet， and medical treatment options and we may be more susceptible to certain diseases than our ancestors were.

However， both then and now， all these genetic effects are modulated by the environment. For most traits， MS included， the genetic effects are the result of multiple genetic variants. Ultimately， we can’t say that MS came from Bronze Age populations， but these populations’ movements and environments contribute to differences in MS risk today.

（材料出自CNN網站，有删改）

1. What can we know about the research？

A. Comparison was made between current DNA and ancient ones.

B. It indicates ancient genes still has protective benefits.

C. It indicates ancient genes are the major causes of MS.

D. The causes of MS were widely known before the study.

2. What does “prone” underlined in Paragraph 4 refer to？

A. Hard to imagine.

B. Extremely uncommon.

C. Resistant to a disease.

D. Easily infected.

3. What was the result of the specific genetic variants in Paragraph 5？

A. It contributed to the change in people’s agricultural development.

B. It made Yamnaya highly mobile.

C. It made Yamnaya weigh heavily on their life.

D. It led to Yamnaya’s movement to the western Europe.

4. Which statement will the author probably agree with？

A. Genetic variants is usually considered useful.

B. Genetic effects correlates with surroundings.

C. The environment have little impact on genetic effects.

D. Genetic variants was of little use in Bronze Age.

1. A。解析：细节理解题。材料第三段大意为“通过将古代DNA与现代样本进行比较，研究人员对当今的衰弱性疾病和身体特征有了新的生物学理解”，选项A的意思为“比较了现有的和古代的DNA”，故选A。

2. D。解析：词义猜测题。材料第四段最后两句的大意为——研究指出北欧人是最容易患上这种疾病的人群之一，但人们对相关原因却知之甚少；通过使用该数据库，研究人员发现，患有这种疾病的遗传风险与一群古代牧民的血统占比相关。据此，“prone”应该指的是容易患病，故选D。

3. A。解析：细节理解题。根据材料第五段最后一句中的“these genetic variants may be beneficial to European populations in making the shift from hunting and gathering to farming”，我們可知这些基因变异可能有利于欧洲人从狩猎和采集到耕作的转变，故选A。

4. B。解析：推理判断题。材料最后一段中的第二句提到“对于包括多发性硬化症在内的大多数性状来说，遗传效应是多种遗传变异的结果”，由此可推出“遗传效应与周围环境相关”，故选B。