It is not known for sure which species actually created and used Oldowan tools. It reached its peak with early species of "Homo" such as "H. habilis" and "H. ergaster". Early "Homo erectus" appears to inherit Oldowan technology and refines it into the Acheulean industry beginning 1.7 million years ago. Oldowan tools are sometimes called "pebble tools", so named because the blanks chosen for their production already resemble, in pebble form, the final product. Oldowan tools are sometimes subdivided into types, such as chopper, scrapers and pounders, as these seem to be their main uses.