Just a quick mention of these interesting findings. The tools found by Thomas Plummer's team in Kenya are the oldest Olduwayan style tools found in what used to be a savannah habitat (there are older ones but belong to jungle ecosystem). For this reason the researchers are quite confident that they do belong to members of the genus Homo. The oldest dates considered at the moment were of some 1.8 million years.
Thomas W. Plummer et al., Oldest Evidence of Toolmaking Hominins in a Grassland-Dominated Ecosystem. PLoS ONE, 2009 (free access like all PLoS materials).