The discovery by Meave Leakey, a member of a famous family of paleontologists, shows that two species of early human ancestors lived at the same time in Kenya. That pokes holes in the chief theory of man's early evolution — that one of those species evolved from the other.Now, without going into the fact that Homo habilis, the 'great-grandmother' they're talking about here, is kind of a trash-can species, and many anthropologists (namely, my Biological Anthropology professor) argue that it may not even be a separate species, that is not what this discovery is the equivalent of. Rather, it's like finding out your grandmother and great-grandmother were alive at the same time and lived in the same house for awhile. Which I'm willing to bet they did.
...It's the equivalent of finding that your grandmother and great-grandmother were sisters rather than mother-daughter, said study co-author Fred Spoor, a professor of evolutionary anatomy at the University College in London.
The article goes on to make several references to how this proves a 'bush' theory of evolutionary development over a 'ladder' theory, with a more linear development. This seems to me to show a huge misunderstanding in the way both evolution and the fossil record works, and scientist's understanding of them. Of course human evolutionary development is more 'bushy.' That's how evolution works. No anthropologist I've ever studied under, talked to, or whatever has believed this. The evolutionary trees of modern animals are 'bushy.' Why would humans be any different?
The reason that it may seem, with the fossil specimens we have, to be 'ladderish' is because we have so few fossils. The conditions that created, say, Lucy or Turkana Boy in the first place are exceedingly rare. Then you have to consider that they went millions of years without being destroyed and that we happened upon them in the first place. The amount of fossils undiscovered, combined with the amount of fossils already destroyed and the amount of individuals that were never fossilized in the first place is probably overwhelmingly huge.
(Now this is not to say that evolutionary theory is somehow flawed - even with our sparse information, the theory stands. It's like making a map of a coastline you're exploring. Just because you have to keep adding details to the map as you find out new things doesn't mean that maps are 'wrong.')
I blame cheesy articles like this one, combined with poor science education, for the lack of understanding regarding human evolution in the general public. It's really not that complicated to not explain it stupidly.
**Added** Quoth PZ Myers (whose grammar is much more coherent than mine):
These discoveries do not put any seriously held theories in doubt. They do nicely demonstrate that a linear progression is not to be seriously held.What he said.
Just as your mother's life most likely substantially overlapped with your own, the persistence of a parental species so that it overlaps in time with its daughter species is not a challenge to evolution at all.