New evidence in form of unmistakable stone-tools' marks on bone, push back the earliest known systematic use of tools to an species that was surely not still "human" (in the sense of belonging to the genus Homo) but to Australopithecus afarensis or another similar (but unknown) species. This happened some 3.4 million years ago in the central-northern Ethiopian highlands.
Australopithecus afarensis, the species to which the famous fossil Lucy belonged to, is the only hominin species known to have lived in that space-time. However until now it was commonplace to think that they were vegetarians and did not use tools.
It seems now that such ideas were wrong and that Lucy's species, with a brain barely larger than that of a chimpanzee, was already using not just random rocks but sharp ones able to cut meat. Forensic analysis leaves no room to doubt the marks are product of cutting tools and not animal fangs or paws.
This has potentially interesting implications for the evolutionary history of human brain and intelligence, as well as our highly precise hand, both tightly associated to tool use.
More detailed news stories at Science Daily and BBC.
Ref. Shannon P. McPherron et al., Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature, 2010. Pay per view.