ERFKROON, South Africa -- James Brink surveys the pink and yellow flags that dot the mounds of an old riverbed here and wonders if he will add another twist to the "Out of Africa" saga.

Not the romantic drama by Isak Dinesen, brought to the screen by Robert Redford and Meryl Streep, but the scientific thriller suggesting that all modern humans -- black, brown, white and yellow -- are descendants of African progenitors.

There is no doubt among the experts that ancient man, or Homo erectus, emerged from Africa about 1.5 million years ago. The latest suggestion is that there was a second exodus from the continent, a mere 100,000 to 150,000 years or so ago, when Homo sapiens became a globe-trotter.

"The idea is gaining ground," said Brink, a paleoanthropologist who specializes in mammal fossils of the past 2 million years. "As more fossils are discovered and as we do more dating, I believe it all points back to the African origins of modern man."

Brink is spending this month in South Africa, surveying the old bed of the Modder River on a remote Orange Free State farm outside Bloemfontein to decide whether it is worth conducting a major dig here. On the eroded surface, there are only animal fossils, bone and teeth, and a plethora of flint implements. Should he unearth any human remains, it would be a major find.

"Everybody wants to find a hominid," or early human, said Katherine Brust, a Duke University graduate student who is helping mark the animal remains with colored flags.

"It would be a great moment," said Brink. "If we find humans, then at least there is some kind of context [from the rest of the fossils] for them."

At his research station at nearby Florisbad Springs, Brink keeps a cast of the 260,000-year-old partial skull of Florisbad man. In other parts of the world, traces of modern humans date back only 50,000 years or less.

"The documentation of the origin of the modern anatomy is only available in Africa," says Gunter Brauer, professor of paleoanthropology at Germany's Hamburg University and originator of the "Out of Africa" theory. "We have, in other parts of the world, good reason to assume there was not such a process."

While the "Out of Africa" concept is gaining ground, not everyone is convinced.

"Homo sapiens didn't suddenly pack his suitcase between 100,000 and 200,000 years ago and say, 'I'm off to Europe and I'm going to stay there,' " said Ron Clarke, paleoanthropologist with Witwatersrand University in Johannesburg.

"From what one knows of human history, people have always moved around," he said. "You only stay in a place if you have a good standard of living, whether you happen to be a gorilla, a chimpanzee or human being.

"If, however, you have a lack of water and a lack of food, or aggressive animals or people are harassing you, you move on. I think modern man could have occurred all over the world."

This sort of thinking has produced the "multi-regionalist" concept, which sees modern man developing as the result of intermingling or hybridization between African emigrants and archaic local species, such as Peking man in China and Java man in Indonesia.

"These [human intermingling] processes are going on right now," says Alan Thorne, of the Australian National University, Canberra, and a leading multi-regionalist. "There is no reason to believe that has not been going on the whole time since we have been a species.

"I don't see a series of extinct species. I see different species evolving. We know that humans evolved in Africa, and nowhere else. But sometime between 1 million and 1.5 million years ago, they began to take international holidays.

"For me, modern humanity emerged in slow steps. One day in China, there might have been motivation for a better form of speech. At the same time, the knee joint improved in Africa and a better form of spear-throwing developed in Europe. These ideas moved back and forth, so the whole of humanity moved toward modernity."

This form of continuous evolution, according to Thorne, explains racial and regional differences.

But Christopher Stringer, researcher in human origins at London's National History Museum and an ardent member of the "Out of Africa" school, argues that physical evidence reveals that racial and regional differences emerged only during the past 30,000 years, much more recently than previously thought.

They are, according to Stringer, the likely result of differences in diet, climate, geography and natural selection rather than hybridization.

"I do believe we are talking about a single origin," said Stringer. "The evidence certainly supports that the origin occurred in Africa."

If there is still controversy over the origins and movement of modern humans, there is broad consensus that man's primitive forebears were certainly "Out of Africa."

Paleoanthropologists in eastern Africa are digging and scraping their way closer to those beginnings. The holy grail for them is the elusive "missing link," the apelike common ancestor of man and chimpanzee.

The common ancestor is believed to have lived in Africa 5 million to 6 million years ago, developing into the two distinct but similar species, with the split probably influenced by geographic, climatic or dietetic differences.

The earliest traces of hominids have been unearthed in eastern Africa. The oldest species, Ardipithecus ramidus, traced to 4.39 million years ago, was found in Ethiopia's Middle Awash Valley in 1992 by a team led by Tim D. White, research paleoanthropologist from the University of California.

Crawling shoulder-to-shoulder across earth so hot it blistered their hands, White and his team unearthed the remains of what he calls "the most fragmentary and fragile fossil hominid ever found."

The dig yielded a fairly complete foot and hand, some long bones and portions of skulls. Extracting them, said White, was like getting a piece of school chalk out of a block of concrete. The bones are being analyzed in a laboratory in Addis Ababa, the Ethiopian capital.

One thing they are likely to reveal: whether Ardipithecus was a knuckle-walker like an ape or had the upright gait of a human.

"I think it will show an animal that is not a chimp and not a human, and effectively not of this world, meaning the modern world.

"We evolved from some creature, and Ardipithecus is that creature we evolved from," said White. "There was a Y-fork between the chimp and the human. It is the last link in the chain going toward that common ancestor."

Close to where Ardipithecus was found, the search has now begun, in terrain dated 5 million to 6 million years old, for its forebear -- the common ancestor.

Ardipithecus, according to White, cannot be that link. The common ancestor will have no exclusively human features, such as Ardipithecus' humanlike small teeth and extended thumb.

"It means it had already evolved toward us," White said of Ardipithecus. "What we have found is what appears to be the rTC first link in the exclusively human chain."

Pub Date: 8/03/98