VOA慢速英语 2007 0904b（在线收听）

VOICE ONE:

This is SCIENCE IN THE NEWS in VOA Special English. I'm Faith Lapidus.

VOICE TWO:

And I'm Steve Ember. This week, we will tell how a discovery in Kenya has started a scientific debate about early human ancestors. We also will tell how people might have influenced the diet of birds on Antarctica. And, we will answer a question from Vietnam about an eye disease.

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VOICE ONE:

 
A complete Homo erectus skull and the upper jaw of Homo habilis at a news conference at the National Museum of Kenya
A team of researchers recently announced discovery of two fossils that it says should change the theory of human development. The Koobi Fora Research Project says the fossils came from two ancestors of human beings. Their remains were discovered seven years ago in Kenya.  The British magazine Nature published a report on the discovery.

One fossil is an upper jawbone -- a long curved bone along the mouth. The other is a skull -- the bone that holds and helps protects the brain. The researchers say the upper jawbone is about one million four hundred forty thousand years old. They believe the skull fossil is even older.  It is believed to be about one million five hundred fifty thousand years old. 

VOICE TWO:

Anthropologists Maeve Leakey and her daughter, Louise, are leading the Koobi Fora Project. They say the jawbone belonged to the early human ancestor Homo habilis. They say it is from a period when scientists thought Homo habilis had already disappeared from Earth. 

The Leakeys say the discovery means that Homo habilis lived at the same time as Homo erectus. If confirmed, that could change scientific theories about the development of modern human beings. 

VOICE ONE:

Many scientists believe that humans, or Homo sapiens, developed from Homo erectus. They also believe that Homo erectus developed from Homo habilis.

The Leakeys say the shared period of existence makes it unlikely that Homo erectus developed from Homo habilis. They say both species probably developed two million to three million years ago. And, they say, the long period as separate species probably means they were not competing for food and shelter. They survived as species using different methods.

Other anthropologists are not persuaded that the jawbone forces a change in the theory of human development. They say it is likely that the Leakey's mistakenly identified a Homo erectus jawbone as a Homo habilis one.

VOICE TWO:

The Koobi Fora Project researchers also found a skull they identified Homo erectus. However, it is the smallest Homo erectus skull ever found. The researchers say the small skull suggests a sexual dimorphism was common among the Homo erectus species. Sexual dimorphism is when the size difference between the sexes is great. This quality would make Homo erectus closer to gorillas than human beings.

But, other scientists argue that what the researchers found is simply the skull of a very young Homo erectus, not of a small adult. They also say two fossils are not enough evidence to change a theory of development based on hundreds of finds.

There are also fossil experts who support the Leakey findings. They note that the skull found is in especially good condition making identification easier.

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VOICE ONE:

You are listening to SCIENCE IN THE NEWS in VOA Special English.  With Steve Ember. I'm Faith Lapidus in Washington.

 
Adelie penguin
Two hundred years ago, Adelie penguins ate a diet rich in fish along the coast of Antarctica. But researchers say the diet of these black and white birds is very different now. They say the penguins began to depend on small sea organisms for food after fish populations decreased.

Scientists from universities in the United States and Canada announced the discovery. They reported their findings in the Proceedings of the National Academy of Sciences.

VOICE TWO:

Steven Emslie and William Patterson studied the chemistry of the eggshells of Adelie penguins. They used pieces of the shells from Ross Island in the Ross Sea.  Explorers collected the eggs there in the nineteen hundreds. The cold Antarctic climate kept them in good condition. 

The most recent eggs in the study were one hundred years old. The oldest were thirty eight thousand years old. The researchers compared the chemistry of the shells with the chemistry of fish and small sea organisms like krill. 

VOICE ONE:

One finding was surprising. Climate change about ten thousand years ago did not make major changes in what the animals ate, the researchers say. But they found that the chemistry of the eggshells became very different during the past two centuries. The chemistry changed from heavier to lighter isotopes of carbon and nitrogen. Isotopes are a form of chemical element.

The researchers believe that people were important in this change. They say the populations of krill in the southern seas increased after hunters killed almost all the Antarctic fur seals in the nineteenth century. 

VOICE TWO:

In the twentieth century, hunting of whales greatly decreased the whale population. Whales and seals eat large amounts of krill. So the reduction of those animals increased the krill population. The researchers believe the penguins started eating more krill because it was easily available to them. It was also easier for the birds to gather krill than catch fish.

Today, the population of krill also is threatened by an increased number of krill fisheries. The researchers say climate warming caused by humans also is reducing the sea organisms. They say this means the choice of foods for Adelie penguins has gotten smaller.

Mister Emslie works at the University of North Carolina in Wilmington, North Carolina. Mister Patterson is at the University of Saskatchewan in Saskatoon. 

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VOICE ONE:

The retina is the sensory tissue in the back part of the eye. It gathers light and captures images from the lens, much like film in a camera. The retina processes these images into signals that travel through the optic nerve to the brain.

Diseases of the retina can cause vision loss over time.

A thirty-year-old listener in Vietnam says he cannot see well and doctors have told him he has retinal degeneration. This is the loss or destruction of the sensory tissue of the retina. Trinh Phuong Bac says he first developed problems in his right eye when he was a child. He would like to know more about this disease.

VOICE TWO:

Emily Chew is a deputy division director at America's National Eye Institute. She says it is true what doctors have told our listener: there is no cure for retinal degeneration.

She says most cases are considered genetic. Scientists have been attempting to develop gene treatments for it.  In recent years, there have been some reports of possible progress. But Doctor Chew says these studies of experimental gene therapies have only involved animals.

VOICE ONE:

Recently, the National Eye Institute reported the findings of a study of diet and a disease called retinopathy. It says the omega-three fatty acids EPA and DHA, both found in fish, protected mice against the development and progression of retinopathy. The study showed that decreasing omega-six fatty acids in the diet also helped. The study was published recently in Nature Medicine.

The findings could be useful to research into retinopathy in humans, including a common cause of vision loss in diabetics. A separate form can lead to permanent blindness in babies born too early.

VOICE TWO:

However, Doctor Chew says this study may have no connection to treating retinal degeneration. She also says there is disagreement about whether taking high levels of vitamin A could reduce the severity of the disease. She says one study suggested that vitamin A helped some people with retinitis pigmentosa. But she notes that other investigators have disputed these findings.

Retinitis pigmentosa, or R.P, is a form of retinal degeneration. R.P. is the name for a group of diseases that can be found as early as when a person is a teenager. People with R.P. have genes that give incorrect orders to cells that receive light. As a result, the retina can begin to self-destruct.

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VOICE ONE:

This SCIENCE IN THE NEWS program was written by Jerilyn Watson and Caty Weaver. Brianna Blake was our producer. I'm Faith Lapidus.

VOICE TWO:

And I'm Steve Ember. Read and listen to our programs at voaspecialenglish.com. Join us again at this time next week for more news about science in Special English on the Voice of America.