The oldest tradition of human toolmaking, named after the simple stone tools found at Olduvai Gorge, Tanzania but now known from many other early human occupation sites in Africa. The oldest certain stone tools, from the Hadar and Omo regions in Ethiopia and from the east of the Democratic Republic of Congo, were made between 2.5 and 2 million years ago, probably by Homo habilis. Usually, the toolmaker started with a large cobble, probably picked out of a stream bed, and flaked it with a hammerstone into the required shape. The detached flakes were also trimmed and put to use. Several distinct types of Oldowan tools were made and were probably used for different tasks. A more advanced tradition, Developed Oldowan, occurs also at Olduvai Gorge around 1.5 million years ago, the maker probably being Homo erectus.