NEW YORK — In the decades since a preoccupied German butterfly collector almost tumbled headlong into Olduvai Gorge, this gash in Africa's Serengeti Plains has become known as the Grand Canyon of human evolution.
Other sites have yielded more fossils than Olduvai, but none "has produced the concentration of archeological material, cultural material, that Olduvai has produced," said Tim White, a paleontologist at the University of California, Berkeley.
Donald Johanson, director of the Institute of Human Origins in Berkeley, said: "Here you have definitive association between stone tools, animal bones and early hominids in a very well-understood environment."
Heads Research Project
Johanson is leading a new and enlarged research program at Olduvai in cooperation with the Tanzanian government. The effort resulted in a major find almost as soon as it began in the summer of 1986, suggesting that the gorge has many secrets yet to divulge.
Johanson is to explore the ravine and train Tanzanian paleontologists.
"It's a marvelous, exciting place," said Richard Hay of the University of Illinois in Urbana, who did the definitive research on Olduvai's geology. "It has had a very important catalytic influence on research elsewhere and in developing our present-day notions of our family tree."
But the findings at Olduvai have often confounded paleontologists and provoked lively debate, such as the 1986 discovery of a 1.8-million-year-old skull and partial skeleton of a woman with surprisingly long, apelike arms.
"It tells us something extraordinary, something we've never anticipated before," Johanson said recently. "It must suggest that natural selection was keeping those arms long." The creatures, he said, "were probably participating in some degree of tree climbing."
But Milford Wolpoff, an anthropologist at the University of Michigan, said the hominids may have had long arms for other reasons. "Maybe swinging clubs makes good sense as well."
"I think the question of climbing trees can be handled when there's a good enough analysis of the shoulder," Wolpoff said. "This shouldn't be speculation. Somebody should be able to show they were climbing trees or they (were) not."
Johanson and White say their find represents the species Homo habilis , the first toolmakers.
Collection Too Diverse
But Bernard Wood of Liverpool University in England has pointed out that the collection of skeletons identified as Homo habilis may be too different from one another to be grouped together.
Once again, Olduvai has challenged widely held notions about human evolution.
Olduvai Gorge lies in northeastern Tanzania, 100 miles west of Mt. Kilimanjaro and the same distance south of the Kenyan border. It cuts across a corner of the Serengeti Plains, inhabited only by vast herds of migrating animals and roving bands of Masai tribesmen.
Olduvai is a corruption of the Masai words for "the place of the wild sisal," a reference to the cactus-like plants scattered on Olduvai's slopes.
Lions, leopards and cobras roam the gorge. Its red, brown and gray soils are littered with bones, primitive stone tools and the stone flakes that have been chipped off them.
"There are places you can't walk without stepping on a stone flake," White said.
Smaller Than Grand Canyon
The Y-shaped gorge is 25 miles long and 300 feet deep, much smaller than the Grand Canyon. It is green during the rains of spring and fall, parched in summer and winter. And its elevation on the Serengeti makes it cooler than other East African fossil sites.
"It can get hot, but when one compares it to Koobi Fora in Kenya or the Lucy site in Ethiopia, it's Club Med," White said.
Olduvai developed 500,000 years ago when two streams met and began slowly to slice into the Serengeti's earth. Climate and geography conspired to direct the streams across an ancient oasis where, 2 million years ago, a fresh river emptied into an alkaline lake.
Roving groups of hominids--early humans, their human-like ancestors and extinct cousins--gathered there, ate there and died there, leaving their remains first to be covered by time and then uncovered by the eroding action of water against rock.
A cluster of nearby volcanoes that are now extinct periodically dusted the ground with whitish ash that has, by chance, allowed precise dating of Olduvai's sediments.
"You can stand on the bedrock and gaze at millennium after millennium, stacked neatly as a layer cake," wrote Richard Leakey, an anthropologist and the son of Louis Leakey, who made Olduvai famous.
Sixty-two skeletons of hominids have been uncovered at Olduvai, skeletons that would not have been found if the streams that formed the gorge had meandered even a few miles away from the prehistoric lakeside oasis.