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Earlier protohumans had used tools too -- bits of horn or bone for digging, sticks for fishing termites out of their mounds (something modern chimps still do). But H. habilis deliberately hammered on rocks to crack and flake them into useful shapes. The tools were probably not used for hunting, as anthropologists once thought; H. habilis, on average, was less than 5 ft. tall and weighed under 100 lbs., and it could hardly have competed with the lions and leopards that stalked the African landscape. The hominids were almost certainly scavengers instead, supplementing a mostly vegetarian diet with meat left over from predators' kills. Even other scavengers -- hyenas, jackals and the like -- were stronger and tougher than early humans. But H. habilis presumably had the intelligence to anticipate the habits of predators and scavengers, and probably used tools to butcher leftovers quickly and get back to safety.
Their adaptations to the rigors of prehistoric African life enabled members of the H. habilis clan to survive as a species for 500,000 years or more, and at least one group of them apparently evolved, around 2 million years B.P., into a taller, stronger, smarter variety of human. From the neck down, Homo erectus, on average about 5 ft. 6 in. tall, was probably almost indistinguishable from a modern human. Above the neck -- well, these were still primitive humans. The skulls have flattened foreheads and prominent brow ridges like those of a gorilla or chimpanzee, and the jawbone shows no hint of anything resembling a chin. Braincases got bigger and bigger over the years, but at first an adult H. erectus probably had a brain no larger than that of a modern four-year-old. Anyone who has spent time with a four-year-old, though, knows that such a brain can perform impressive feats of reasoning and creativity.
H. erectus was an extraordinarily successful and mobile group, so well traveled, in fact, that fossils from the species were first found thousands of miles away from its original home in Africa. In the 1890s, Eugene Dubois, an adventurous Dutch physician, joined his country's army as an excuse to get to the Dutch East Indies (now Indonesia). Dubois agreed with Charles Darwin's idea that early humans and great apes were closely related. Since the East Indies had orangutans, Dubois thought, they might have fossils of the "missing link."
While Dubois didn't find anything like Lucy, he discovered some intriguingly primitive fossils, a skullcap and a leg bone, in eroded sediments along the Solo River in Java. They looked partly human, partly simian, and Dubois decided that they belonged to an ancient race of ape-men. He called his creature Anthropopithecus erectus; its popular name was Java man. Over the next several decades, comparable bones were found in China (Peking man) and finally, starting in the 1950s, in Africa.