The first reason is that Homo habilis is thought to be the direct ancestor of modern man, as opposed to earlier austrolopithecines. Second, the genus Homo is differentiated from earlier hominids (and modern primates) largely by brain size. Homo habilis had a larger brain capacity than its ancestors. It was once believed that Homo habilis was the first hominid to use tools (hence the scientific name, which basically means "handy man.") But subsequent discoveries have demonstrated that earlier hominids used simple tools. It should be noted that Homo habilis is not believed to be the direct ancestor of Homo erectus, and so scientists are unsure of the link between the "handy man" and modern man, though they believe that one exists. Like many of the important australopithicine finds, the first fossils of Homo habilis were discovered by a an expedition led by Louis and Mary Leakey.