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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Barbara Klein.

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And I'm Bob Doughty. Millions of people around the world will celebrate Earth Day on Friday. On our program this week, a report on the health of the world's coral reefs. And we tell about plants that can change their own genes.

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But first, a study that shows how people have affected Earth's environment.

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Experts have released a report that measures damage to the environment from human activities. The report measures the damage to the services that nature provides for people.

The report was released last month. It is part of a project called the Millennium Ecosystem Assessment. United Nations Secretary-General Kofi Annan proposed the project five years ago.

More than one thousand three hundred ecologists and other scientists from ninety-five countries prepared the report. They studied the ability of ecosystems to perform activities like providing food and making water pure. An ecosystem is a group of living things and the environment in which they live.

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The report says people have changed ecosystems to meet growing demands for food, fresh water, and energy. These changes have helped improve the lives of thousands of millions of people. But they have weakened the ability of nature to provide important services for people.

The report identified several problems. They include reduced numbers of fish in the world's oceans and dangers to people living in dry areas. Another problem is a growing threat to ecosystems from climate change and pollution.

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The study found that sixty percent of the world's ecosystems are being harmed by human actions. These include fishing too much and clearing land to grow crops.

The study considered many kinds of services that an ecosystem provides. These include things like a forest's ability to store water and cool the air. It also includes cultural services, like providing a place for recreation. And, it includes life-support services like soil formation and the process by which plants make food.

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The scientists say many of the areas where the environment is most quickly being damaged are among the world's poorest areas. As a result, they said, damaged environments are likely to harm efforts to help poor people and reduce disease in developing countries.

The report said rich countries also were responsible for some problems. One of them is the increased use of chemical fertilizers. The fertilizers are washed into rivers and coastal waters. Nitrogen in the fertilizers creates areas in the water where nothing can live.

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Many earlier studies examined loss of forests and other wild places on land and in the oceans. The new report also deals with losses in dry-land ecosystems.

The scientists say this is where human populations are growing fastest and depend most heavily on natural systems. One example is Africa south of the Sahara Desert. That is where they say dry conditions and growing demands for water have added to social problems.

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The report says action is needed to prevent additional damage to the environment. The scientists who led the project released a statement. It says: "We must learn to recognize the true value of nature – both in an economic sense and in the richness it provides to our lives."

The statement also said protecting the environment should no longer be seen as something a country considers after more important concerns are dealt with. It said measures to protect natural resources are more likely to be successful if local communities are involved in decisions and share the gains.

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Another report says the world's coral reefs are in trouble. It warns that more than two-thirds of the reefs are threatened or have been destroyed.

Two hundred forty scientists from more than ninety countries studied the condition of corals worldwide.

Corals are groups of small organisms, called polyps. They live within a skeleton made of a substance called limestone. Corals are found in warm water. Millions of corals grow together to form coral reefs. The reefs support many kinds of sea life. Reefs protect coastal communities in storms. They also can be important to local and national economies.

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The Global Coral Reef Monitoring Network produced the report. Clive Wilkinson is coordinator of the group. He says the problems are everywhere. In the Persian Gulf, for example, sixty-five percent of the coral reefs have been destroyed. South and Southeast Asia have lost nearly half their reef cover.

The report names several threats to coral reefs. They include pollution, coastal development, poor land use, and destructive fishing activities. Rising ocean temperatures are another problem. This causes a damaging condition called bleaching, or whitening.

Higher than normal water temperatures cause corals to expel the small plants they feed on. If the water stays too warm, the corals die. Mister Wilkinson says extreme weather severely damaged coral reefs seven years ago. Some of the reefs are recovering. Yet, Mister Wilkinson says many reefs show little signs of renewal.

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The report urges governments, lending organizations, international agencies, and environmental groups to work together to protect coral reefs.

Mister Wilkinson says Australia has taken the lead by expanding protected areas around the Great Barrier Reef. This reef extends more than two thousand kilometers along Australia's northeast coast. Scientists believe the Great Barrier Reef is about thirty million years old. It is the largest group of coral reefs in the world.

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Last year, the Australian government declared one-third of the reef a "no-take zone." The government barred fishing there. People also are barred from collecting live fish or coral in the area.

The Global Coral Reef Monitoring Network supports protected no-take zones. The group also called for a reduction in pollution and a ban of destructive fishing activities. Clive Wilkinson says the coral reefs can recover. But he believes more government involvement is needed.

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American scientists have discovered that some plants are able to correct mistakes in their own genetic material. They say the plants do this by using other genes passed to them from plant ancestors.

The scientists reported their work in the publication Nature. They say that understanding how this gene correction takes place will make it possible to develop new kinds of crops. They also say scientists could learn how to use the process to control the genetic mistakes that lead to disease.

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The discovery appears to dispute the scientific laws of heredity first described by Gregor Mendel in the nineteenth century. Mendel observed how some qualities in plants were passed down from their immediate ancestors, but others were not. He proposed the laws of heredity to explain this. His theory says plants get their qualities from their ancestors. Now, scientists at Purdue University in Indiana say his work may need to be re-examined.

The Purdue scientists studied one kind of plant called Arabidopsis. Arabidopsis is self-reproducing. This means it does not need anything from another plant to reproduce. Some of the plants had a changed gene that caused its flowers to grow together instead of separately.

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Mendel's laws would lead scientists to believe the resulting plants of reproduction also should have the changed gene. The scientists found, however, that ten percent of the resulting plants had no copy of the changed gene.

The scientists studied Arabidopsis for more than a year before they found the plant was fixing itself. They believe that the plant had been storing much more genetic information than anyone had ever thought.

Some of the information came from ancestors that were already dead. The scientists say this other information is affecting the plant so that it does not have the changed gene.

The American scientists still do not understand how this is happening. The scientists say they want to investigate a possible similar genetic situation in animals.

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This program was written by Shelly Gollust, Jill Moss and Edward Stautberg. Cynthia Kirk was our producer. I'm Bob Doughty.

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And I'm Barbara Klein. Join us again next week for SCIENCE IN THE NEWS in VOA Special English.