The Olduvai Gorge in northern Tanzania has a geology that fossil-hunters love. A river cuts through several layers of strata with four distinct beds. Bed I, the oldest, is about 2 million years old.

From the late 1930s, Louis and Mary Leakey found stone tools in Olduvai and elsewhere, found several extinct vertebrates, including the 25-million-year-old Pronconsul primate, one of the first and few fossil ape skulls to be found. Their work at Olduvai Gorge had been interrupted by political uprisings in nearby Kenya, but late in the 1950s, they returned. The Leakeys were interested in prehistoric tools, but more and more wanted to find evidence of the people who made them. In 1959, they did.

Louis (also known as L.S.B.) Leakey wrote about their discovery for National Geographic magazine in 1960: He had a terrible headache and high fever. Mary Leakey insisted he rest that day and recover; if he got worse they'd have to leave the site. Mary went out to work as usual. That day, she found fossilized parts of the upper teeth and skull of a hominid no one had recorded before, eroding out of an area near Bed I. In the next three weeks the Leakeys found more than 400 pieces to comprise an almost complete skull. It was not too different from remains found in South Africa by Raymond Dart in 1924 and by Robert Broom in 1936. (Those finds had not been accurately dated because of the way they were found and the lack of dating technology.) But the Leakeys thought their find different enough to constitute a new category of hominids, and called it Zinjanthropus boisei. They suggested that it lived 1.75 million years agoÑmaking it by far the oldest hominid yet found.

In 1960, Mary Leakey and son Jonathan found another, smaller form of hominid at Olduvai that they believed was different and more advanced. They called it Homo habilis (handy human) because it appeared to be the first human to use tools. The designation of these two new groups raised a great deal of controversy. Zinjanthropus has since been put by most scientists into the Australopithecine genus, which the South African finds also belong to, though in different species. Homo habilis is now widely accepted, dating back about 2 million years. The 1972 discovery by the Leakeys' son Richard of another Homo habilis (often called Turkana Boy or ER-1470), dated to 1,900,000 years ago, helped confirm this. It also supported L.S.B. Leakey's startling suggestion that the Homo genus did not evolve from Australopithecus, but that parallel lineages of hominids were developing at the same time.

The Leakey's finds were spectacular and brought popular attention to the field of paleoanthropology. Public support and interest meant more funding for more expeditions. The number of fossils discovered in East Africa in the next decade caused both confusion and controversy, but ultimately a greater knowledge of early human history.

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