That finding, announced in August, set the world of anthropology spinning. Once again notions about the early history of human origins had been challenged. And once again it was a member of the Leakey family - anthropology's most famous clan - who was stirring the kettle of controversy.
Leakey, who is the director of the National Museums of Kenya, spoke about the black skull and other discoveries during a recent interview at the National Geographic Society in Washington. He will elaborate on his findings tonight during a lecture at the University Museum, as part of that institution's 100th-anniversary activities. Tickets to the lecture are sold out.
During the last 40 years the Leakey name has become synonymous with the study of human origins. Discoveries by his parents - Louis and Mary Leakey - and himself have been instrumental in understanding how humans evolved.
The Leakeys have helped transform paleoanthropology, the study of the early history of humans, from the relatively simple search for ancient fossils into a sophisticated science that utilizes the latest technological tools.
The Leakeys proved beyond a shadow of doubt that humans originated in Africa, rather than Asia as had earlier been believed. They discovered and named the bones of the first human toolmakers, Homo habilis, and dug up the most complete skeleton of a more recent ancestor, Homo erectus. They found 3.7 million-year-old fossil footprints showing that human ancestors walked upright long before they made tools.
But the Leakeys also have been immersed in controversy. While they have discovered some of the world's most important fossils, they have, on occasion, been proven wrong about the inferences they have drawn from their discoveries.
Some experts disagree with Richard Leakey's frequent contention that man is innately cooperative and food-sharing, rather than a bloody aggressor. They say that there is little evidence to support that view.
Leakey, 41, argues, however, that there is even less scientific evidence to support the widely held belief that prehistoric people were aggressive and
violent. "Many people grew up with images drawn from comics of the cave man as the hairy brute who used to beat fellow brutes on the head in the course of stealing women and dragging away victims," he said. "No weapons of death and destruction - no clubs - have been found. The evidence for aggression and violence does not exist."
Nor is Leakey shy about putting forward the view that the first people were probably black. "It is likely because dark skin would have been required for living in the tropics," he said.
During the last decade Leakey has been engaged in a sometimes bitter dispute over the interpretation of early human fossils put forward by Donald Johanson, an anthropologist at the University of California at Berkeley.
The dispute stems from the discovery by Johanson in 1974 of a rich collection of human fossils in Ethiopia. Johanson, so overwhelmed with his three million-year-old find, christened the bones "Lucy," then serenaded the African desert with the Beatles' song, "Lucy in the Sky With Diamonds."
Johanson and Timothy White, a collaborator at Berkeley, contend that the bones belong to a single species and have named it Australopithecus afarensis. They have maintained that these fossils represent the long-sought "missing link" in evolution - a common ancestor of both humans and a humanlike creature called Australopithecus that became extinct about a million years ago.
Johanson says that although the afarensis species walked on two legs, it had a very small brain and cannot be considered human. He believes that humans evolved from the afarensis species about three million years ago.
Leakey disputes the interpretation that Johanson found a new species, arguing that the Ethiopian fossils represent two different species that coexisted at the time, much as people and great apes coexist today. "We think there might be chicken eggs and duck eggs all thrown together in the same basket," he said.
Leakey believes that the origins of humans are more complex than Johanson believes and that the "missing link" between apes and humans has not yet been discovered. He believes that fossils yet to be found will show that humans first developed up to five million years ago.
That is why the discovery of the black skull in August 1985 by his colleague, Alan Walker of Johns Hopkins University, is considered important. Leakey and Walker believe that the age of the skull - almost as old as Lucy - makes it unlikely that it directly evolved from Lucy.
"This throws cold water on the notion that as recently as three million years ago there was only one species of early man which gave rise to the others," Leakey said. "This is probably more significant than anything we've had for a good number of years."
Other experts agree with Leakey that the find is significant. "This skull is the most exciting find since Lucy," said Eric Delson, an anthropologist at the City University of New York's Lehman College.
Leakey maintains that the media has made too much of his dispute with Johanson. "I'm reluctant to fan the flames of controversy," he said. "The media is creating the disagreement."
He acknowledges that the discovery of the black skull will not end the controversy over the Lucy fossils. "It adds fuel to the discussion but it surely won't resolve it," he said.
Leakey, who spends about 60 days in the field each year with his team of about a dozen scientists, intends to keep searching for human fossils. He says he has no plans to write a book about his recent findings or to take part in a scientific television series, as he did in 1981 in The Making of Mankind.
He said that he expects to continue working at the Lake Turkana site in northern Kenya for 15 to 20 more years and that there is a "good chance" that scientists will eventually find the fossils that will support his views of the complex early history of people.
And he makes no bones about the fact that he hopes it will be he who makes the major discoveries. "We intend to continue our work, probing, pushing, learning as much as we can," he said.