FOR 165 million years after the island of Madagascar tore loose from the African continent, creatures living there evolved in isolation from the larger world. Birds, plants, and animals that were eliminated by competition elsewhere flourished in the forests. Gentle, primitive lemurs were the only primates to emerge. Today, two-thirds of the rain forest has been cleared for pasture land and fuel. With their habitat gone, these creatures, found nowhere else on earth, are disappearing. Scientists believe that if present trends continue, many of the 40 known subspecies of lemurs on Madagascar, the world's fourth-largest island, will be extinct by the year 2000.
But man can protect as well as destroy. Scientific curiosity, economic incentives, and man's sense of affinity with all life have joined to protect the future of Madagascar's treasures.
Madagascar, about twice the size of Arizona, now has 11 nature reserves. With help from the Duke University Primate Center in Durham, N.C., and the World Wildlife Fund it is establishing its third national park. Officials hope that the preserves can attract foreign visitors and generate income for the country.
``Our first priority is to save what is left of the habitat - to establish the parks on Madagascar,'' says Elwyn Simons, a paleontologist and the director of the Duke primate center. This year the center signed an accord with the island government for a joint program of conservation, education, and research to help prevent extinction of the lemurs.
Hunting and logging are still widespread in the preserves, and game wardens lack funds and vehicles to combat the pressures of an expanding population. Eighty percent of Madagascar's 10 million people live by hunting and farming. Many do not know that lemurs and other creatures are unique to the island.
As a ``second line of defense,'' the Duke primate center has bred the world's largest colony of lemurs in captivity. Scientists hope that someday they may be able to release the captive-bred animals safely in their natural home.
With their primitive and sometimes disturbing resemblance to man, lemurs inspire a range of responses from man. Their apposable thumbs (similar to man's), gripping hands, and fingernails look uncannily human.
On Madagascar, the erect and child-size western sifaka lemurs are protected by the local belief that they are ``men of the forest.'' But the nocturnal aye-aye lemurs are feared as an omen of death and often are killed on sight.
Apart from their historical significance, lemurs fascinate scientists with their diversity. On Madagascar, they have evolved into 13 genera, 26 species, and 40 known subspecies. The smallest, the mouse lemur, is the size of a newborn kitten. The indiri is about the size of a three-year-old child. Some species are nocturnal and others diurnal, some arboreal and others terrestrial, some vegetarian and others omnivorous.
Lemurs are also noted for their generally gentle behavior, ``their calm attitude about life,'' says Pat Wright, an anthropologist who is associated with the Duke center.
``Sometimes I think it would do us all good to sit and watch a bamboo lemur for a while,'' says Dr. Wright, who has spent many seasons in the Madagascar forest watching groups of lemurs peacefully munching bamboo.
Since 1972 the Duke primate center has been the only US group permitted by the Madagascar government to take lemurs from their natural habitat. The center is able to breed lemurs much faster than they would naturally reproduce in the arduous conditions of the wild. About 90 percent of the 537 lemurs at the primate center were born in the last 17 years.
All the center's research is benign, designed to monitor the behavior, health, and reproductive cycles of the captive animals and learn their needs.
``We only ... do things you might do for your own children,'' says Dr. Simons, adding that most of the scientists who work with the lemurs ``feel they are very beautiful and very gentle and vulnerable because they are so endangered.''
When a new lemur is brought to the center, it is kept indoors and carefully watched for its tastes and preferences. Its choice of foods includes bamboo grown in the North Carolina forest, mango, mimosa, sumac, and tropical fruits. Walls of the indoor enclosures are painted deep green and crisscrossed with branches and kudzu vines.
Outdoors, ringtailed and ruffed lemurs live in four natural habitat enclosures of one to 12 acres. Here scientists monitor how closely the behavior of captive-born animals resembles that of those born in the wild.
Unlike chimpanzees, which have to be taught basic skills when returned to the wild, lemurs act in largely instinctive ways, says Kay Izard, a reproductive psychologist. Even captive-born lemurs find as many as 20 types of plants they can eat in the North Carolina forest. They avoid poisonous plants and give proper warning calls for ground predators and birds of prey. After acclimatization, they could adapt to a free life in Madagascar, Dr. Izard believes.
To make that return possible, scientists from the Duke primate center are helping to plan education programs for the island's schoolchildren and setting up a captive-breeding program in a zoo on the island. Pat Wright is working with villages to develop alternatives to logging and hunting in the forests.
``The government of Madagascar is well aware now of the importance of their wildlife,'' says anthropologist Wright, who believes that the day will come when lemurs can be returned to their natural home. Then the peaceful and exotic creatures will again lounge in tops of 65-foot bamboo and warm themselves in the bright Madagascar sun.