This is just my opinion, of course, but I believe that no matter how good the research, given the incomplete nature of the fossil record there will never be any deterministic way to differeniate sibling and cousin species from ancestor species. Hence we'll never know for certain the human evolutionary path.
The analyses we're provided are based upon the fossils we have found, because after all we can't analyze what we don't have. But like the drunk looking for his contact lens under the lamplight because the light is better there, they analyze the fossils they have because they can do no more, even though this effort is perhaps doomed due to lack of fossils either still buried unfound in the ground, or perhaps not even preserved in any way at all. There is no guarantee that a fossil record will be made of a species.
In the end this reduces the matter to one of opinion, which is why many hominid paleontologists are not on speaking terms with each other.
--Percy
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