全新版大学英语听说教程第三册 Unit 08（在线收听）

Unit 8

Part B

Text 1

Why Are Some People Left-handed?

Research has shown that 90% of people naturally use their right hands for most tasks. But hundreds of millions of people use their left hands. Then why are some people left-handed? Scientists have been trying to answer that question for many years. A study done in 1992 found that men are more likely to be left-handed than women. It also found that Asian or Hispanic people are less likely to be left-handed than white people, black people or North American Indians. Some cultures accept people who do things mostly with their left hands. Others do not.

Scientists want to know the reason for left-handedness because it is closely linked to mental problems and language difficulties. One idea about the cause of left-handedness is the genetic theory. It says that people are right- or left-handed because of genes passed to them by their parents. For example, it has been shown that the handedness of adopted children is more likely to follow that of their birth parents than their adopted parents. Other evidence of genetic involvement can be found in some families. One famous example is the left-handed members of the present British royal family. These include Queen Elizabeth II, Prince Charles and Prince William.

Another idea is that right-handed people are born with the gene for it. But about 20% of people do not have the right-handed gene. These people could be either left- or right-handed. This idea may explain why two babies who have the same genes use different hands. In 18% of identical twins one twin is right-handed, and the other is left-handed. Probably both twins lack the right-handed gene so each has a chance to be either right- or left-handed.

Some scientists believe that the cause of handedness could include both genetics and development.

Questions:

1. What is the passage mainly about?

2. Which of the following topics is discussed in more detail in the passage?

3. What did the speaker want to convey by an example of the present British royal family?

4. What conclusion can you draw from the passage?

Text 2

Does Being Left-handed Affect One's Life?

There are approximately 30 million left-handed people in the United States, and several hundred million more around the world. Most right-handed people have never even considered the possibility that there might be any serious issues affecting left-handers. Even among all of these left-handed people, there are many different opinions about what these issues are and which issues might be most important to them.

Some left-handers think that being left-handed is a positive factor in their lives, and they feel that there are no serious issues affecting them. Others think that being left-handed is not a significant factor and has not affected their lives one way or another. There are also some left-handers who have no opinion and have never given any thought to what being left-handed has meant to them. But the majority of left-handed people find that being left-handed is at least a small disadvantage and a minor source of frustration in their lives.

There are many things that right-handed people take for granted that are quite difficult for left-handers. These include many basic skills like learning to write, learning to use scissors and other hand tools and utensils, and learning various crafts and other activities. Sometimes left-handers are puzzled by equipment designed for right-handers, and other times they are confused by instructors and instructions geared toward teaching right-handers. For some left-handed people this amounts to occasional difficulties and minor inconveniences. For other left-handers it is a lifetime full of failures and frustrations that may lead to much more serious problems.

Questions:

1. What is the speaker's attitude toward left-handers?

2. What can be inferred from the passage about right-handers?

3. How do the majority of left-handers feel about their left-handedness?

Part C

Left-handedness and Right-handedness in Babies

Approximately 90% of people in the world are naturally right-handed. Why is this so, and are we born one way or the other? The answer to this question is rather complicated.

In babies and young children, no single side becomes dominant until around the age of eight. At 12 weeks, babies usually use both hands equally, but by 16 weeks, they mostly use the left hand for touching. By 24 weeks, they have changed again and start using both hands. Then at 28 weeks, they become one-handed again, although this time it is the right hand that is used more. At 32 weeks, they start using both hands again. When they reach the age of 36 weeks, there is another change, with most babies now preferring to use the left hand. Between 40 and 44 weeks, the right hand is once again more used. At 48 weeks, babies switch to using their left hands again, and then between 52 and 56 weeks, the right hand takes over.

There are further changes still. At 80 weeks, the right hand loses control, and both are used again equally. When the young child reaches the age of two, the right hand takes over again, but between two and a half and three years, both hands are used equally. Things finally become stable at around four years and stay the same until, by the age of eight, one hand is strongly dominant over the other.

Statements:

1. At 12 weeks, both hands become dominant.

2. By 24 weeks, right hand becomes dominant.

3. By 36 weeks, left hand becomes dominant.

4. Between 40 and 44 weeks, both hands become dominant.

5. At 48 weeks, left hand becomes dominant.

6. Between 52 and 56 weeks, both hands becomes dominant.

7. At 80 weeks, both hands become dominant.

8. At the age of two, right hand becomes dominant.

9. Between two and a half and three years, both hands become dominant.

10. By the age of eight, one hand is strongly dominant over the other.

Part D

Brain Organization and Handedness

Scientific studies during the 1970s and early 1980s suggested that differences in left- and right-handers' patterns of brain organization may be associated with differences in skills, abilities, and perhaps even personalities. In the large majority of right-handers, about 98 or 99 percent, speech is controlled by the left side of the brain.

The right side of the brain, however, is usually used for recognizing and remembering faces and understanding relationships in space. In left-handers, it is difficult to know exactly their patterns of brain organization. About 65 to 70 percent of left-handers have speech controlled by the left side of the brain, which is also true of right-handers. But in 30 to 35 percent of left-handers speech is controlled by the right side of the brain. In some left-handers, both sides of the brain are capable of controlling speech.