Listening and Reading Comprehension


1.  Who discovered the Americas?


2.  Who may have discovered the Americas before the Italian sailor?


3.  Why do scientists think the Americas were discovered before the Italian sailor?


4.  Where did scientists find evidence of this theory?


5.  What have scientists determined based on this evidence?


[Lesson Credits:  Listening Building MP3 TOEFL, Track 8]

05 History

M: Okay now. History books teach us that the Italian sailor Christopher Columbus was the first outsider to discover the Americas. He accidentally came across the Americas in 1492 while searching for a better way to get to Asia. Therefore, he is credited as the discoverer of the Americas.

W: But Professor, isn’t there some debate about whether Columbus was the first person to “discover” the Americas?

M: Correct. In fact, that’s what I’m going to cover today. See, new evidence has revealed that the first outsiders to come to America may have been Polynesian. You know, people from the South Pacific islands like Easter Island and Hawaii.

So how do scientists know that Polynesians came to the Americas first, you might ask? They know this through the discovery of an ancient chicken bone.

W: A chicken bone?
M: Yes. Scientists have recently uncovered a chicken

bone off the coast of Chile. Now, chickens aren’t native to South America, so it had to have been brought in by explorers. DNA testing has revealed that the chicken bone belonged to a type of chicken found in the Polynesian Islands.

W: But I’m not sure I’m convinced that a chicken bone disproves that Christopher Columbus came to America first. Couldn’t Columbus or, a later explorer, have brought the chicken bone with him? 



1.  What disease is carried by mosquitoes?


2.  Where does sickle-cell disease occur?


3.  What are sickle-cells?


4.  What happens when a child inherits both sickle-cell traits from both parents?


5.  What happens when someone has the sickle-cell trait? 


[Lesson Credits:  Listening Building MP3 TOEFL, Track 9]

06 Biology

W: Did you know that a harmful disease might actually have evolved as a solution to malaria, a horrible sickness passed on by mosquitoes? Let’s talk a bit about how this occurs.

The disease is known as sickle-cell disease. It occurs when a person’s red blood cells look like sickles, or, uh, are curved-shaped. This causes people to be very sick and eventually kills them. However, not everyone who carries the sickle-cell trait develops the disease. It all comes down to a person’s DNA.

Everyone in the world has a genetic code called DNA. Each person’s DNA contains half their mother’s and half their father’s genetic makeup. There are sometimes random changes in this code, called “mutations.” Sickle-cells are a mutation. Now, some children are born with a sickle-cell trait. This means that they inherited the genetic trait from one parent. They are a carrier of the sickle-cell trait, but they don’t get the disease. The problem occurs when a child inherits the sickle-cell trait from both parents. When this occurs, the child develops sickle-cell disease.

So this means that the sickle-cell trait is bad, right? Not necessarily. See, children with the sickle-cell trait, not the disease, but the trait, are more immune to the malaria parasite. Some scientists believe that the sickle-cell trait developed as a way to protect against malaria. In fact, the people who have the sickle-cell trait almost all come from Africa, an area where malaria is common. This demonstrates that people likely developed the trait to combat malaria. It’s actually a useful trait to have, as long as a child doesn’t inherit it from both parents. So we have an unusual instance of a potentially dangerous mutation saving lives. 

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