About 50 million kinds of plants, animals, and microorganisms have made this planet home since the beginning time. Today there are five to ten million species, two-thirds of which live in the tropics. Thus, 490 million species have become extinct, lost forever. Extinction is the evolutionary fact of life. But natural extinction differs considerably from impending doom now facing the rhino and tens of thousands of plants and other animals. There are two reasons why natural extinction differs from the accelerated extinction now taking today.
First, during the course of millennia old species evolved into new ones. Consequently, many of the 490 million extinct species are represented today by their descendants. Modern extinctions, on the other hand, eliminate species entirely. If the rhino should vanish, it would leave no evolutionary legacy. It would be gone forever.
Second, rate of extinction varies considerably. Even through some species did vanish because of severe climate changes or increasing environmental resistance created by excess predation or disease, the rate of natural extinction was slow compared with today's accelerated extinction. Currently, one vertebrate (backboned) species becomes extinct every nine months, compared with a natural rate of one species every 1,000 years. When plants, insects, and microorganisms are added, the extinction rate climbs to one species a day. Many experts fear that we have entered a new era of extinction unparalleled in the history of the earth.
If the world's population continues to grow and nations continue to destroy wildlife habitat at current rates, many expert predict, an average of 40,000 to 50,000 species will destroyed per a year over the next 20 years. By the end of the century we may be losing one species per hour.
Pandas, blue whales, tigers, and chimpanzees are the endangered species that make the headlines, largely because there are the most appealing or visible victims. But these species are, in fact, only a small part of the picture. Today, about 25,000 species of plants are threatened with extinction-one of every ten plants species on the earth. Far more insect species teeter on brinks on extinction. Interest in less appealing species is often difficult to stir.
Plant and animal extinction results from any underlying forces, such as economics, politics, and psychology. The most important are: habitat alteration, hunting for commercial products, introduction of alien and domestic species, hunting for sport, pest and predator control.
Òåêñò 16. CAN VITAMINS BEAT BACK THE KLLERS?
Vitamins, garlic and fish oils have all been suggested as aids to a longer life. Can fighting disease really be so simple?
Scientists from research centers all round the world claim that foods containing anti-oxidant vitamins can protect the public from developing cancer and might also slow down the growth of early tumors. The long list of other beneficial effects included protection against heart disease, cataracts and the effects of smoking, the delaying of ageing and slowing the progress of Parkinson’s disease.
The latest research reinforces what many experts in disease patterns have long suspected — that a Mediterranean-type diet rich in fish, garlic, olive oil and with plenty of fruit and vegetables can prevent premature death from the leading killer diseases. a report published in The Lancet last week revealed hat a diet rich in fatty fish has a protective effect on the heart. This study from the Medical Research Council's Epidemiology Unit in Cardiff found that men with heart disease who ate two or three kipper meals a week had a lower death rate from all causes than those who reduced their dietary fat intake or increased the amount of fiber they ate.
Fatty fish such as herring, mackerel, sardines, salmon, halibut and trout are high in two essential fatty acids, EPA and DHA. These are known to have a thinning effect on the blood, making it less likely to form clots in the blood vessels.
Fish oils are also believed to have a lowering effect on blood fats. The Cardiff researchers conclude that men with heart disease may reduce their chances of dying prematurely by adding 12 ounces of oily fish to their diet each week.
But this was not the only good news on the nutrition front. It was announced that garlic pills may also reduce mortality among heart disease patients. Studies in West Germany have shown that garlic treatment reduced the death rate by half and the number of non- fatal heart attacks by a third. As with fish the effects are thought to result from a lowering of blood cholesterol and a thinning of the blood.
The British researchers are impressed by the growing evidence of the protective effects of the nutrients contained in fruit and vegetables.
Vitamins are anti-oxidants, vitamin C, vitamin D and beta-carotene. Vitamin C is found in cauliflower , potatoes, sweet potatoes, broccoli, Brussels, sprouts and citrus fruits and vitamin E in vegetable oils, corn oil, sunflower oil, margarine, wheat germ, nuts, whole grains and leafy green vegetables.
Beta-carotene is known as a provitamin because it is partially converted to vitamin A in the body. Unlike vitamin A itself, large quantities are not harmful. It is found in carrots, cress, spinach, broccoli, tomatoes, mangoes, melons, apricots, peaches and oranges.
Anti-oxidant vitamins are said to prevent illness by canceling out the effects of free radicals. These are highly unstable oxygen molecules believed to cause cell damage and possibly promote both cancer and the laying down of fatty deposits in the arteries.
About 178,000 people die of heartdisease and 160,000 of cancer in the U K each year. The concept of reducing the toll of Britain's big two killers simply by eating more sensibly is enticing, but is it really possible? And if so, what other dietary measures should people take to protect their health?