Since science stories tend to come from common pools, they're largely cut-and-pastes, so I've generally only given one source. Home pages and editorials generally give more information, but you can't be sure of the quality, so except in a few cases where I thought those were interesting, I've not given those at all.
First, a big of background. Evolution is not a linear process. There is no real fixed starting point. Further, any given point can die out, continue as it is, diverge in any number of other ways, etc. This makes tracing a path from start to finish extremely difficult. Furthermore, fossils are relatively rare. This means that finds are from random points in this gigantic tree. The conditions required tend to be fairly exacting, especially on land, so multiple generations that can be reliably linked are virtually non-existant.
It doesn't help matters that most fossils (with the possible exception of a recent T. Rex find) lack any organic component. This means that you're forced to work from the shapes of replicas made through geological processes. With no genetic material to test, classification of fossils is mostly done by shape, location and era. There is no guarantee, therefore, that groupings are always going to be valid. Groups, therefore, shift as new finds are made and old theories are shown to not make sense with the new data.
In the specific case of the Great Apes, the lineage has become much clearer as a result of recent finds. In essence, there was one common ancestor to all of the Great Apes. Over time, the Great Apes diverged and specialised according to the conditions around them. About a hundred million years ago, the common ancestor to Chimpanzees and Hominids diverged, somewhere in Africa. Hominids don't seem to have been terribly stable, as they diverged many times over a relatively short span of time, with multiple migrations into the outside world.
Chimpanzees show something quite fascinating about this process. Their DNA is very similar to that of humans. The difference is about 95%, with a margin of error of about 3%. There is no reason to assume Chimpanzees have the same DNA as the common ancestor and may well have mutated at the same rate. This would suggest that the common ancestor may have shared as much as 97.5% of their DNA with modern humans.
Given that the structural difference is high and the generic code is so close, it is self-evident that relatively small changes can make a very big difference.
About five hundred thousand years ago, before Neanderthals evolved, there were multiple groups of hominids living in Europe. It is unclear, at this point, whether these were different species of hominids, or the same but with different cultures. That is a very hot topic of debate. What is known is that they already had some exceptionally fine tools and were able to act in coordinated groups. (A recent find in England shows evidence of a group of hominids who attacked a prehistoric elephant - somewhere between two to three times the size of modern elephants - with nothing more than flint knives.)
Most of these lines died out. Nobody quite knows why, although there are plenty of theories - change in climate, change in population density, some species simply being smarter than others and therefore getting to the food first, etc. There is always another possibility, which is that not all of the other species died out. A very tiny hominid has been found where the brain imprint on the skull clearly shows that it is not even remotely close to homo sapien, as hominids go. These miniature hominids lived at least until 10,000 years ago - well into the timeframe of humans. Local legends suggest (but offer no proof of) them surviving as recent as 200 years ago.
This isn't the only intrigue. The largest of the Great Apes stood at between 9'-12' (about 3 meters, 20 cm +/- 40 cm). This is well within the range of the mythological Nephilim from the Old Testament (Torah). It is possible a fossil find sparked that legend. It is significantly less likely, but still possible, that Great Apes of that size survived long enough for humans to develop memories of them. There are simply not enough finds to be sure, and digging up large amounts of the Middle East right now would seem to be a Really Bad Idea.
- Evidence exists for a new species of Great Ape, somewhere between Gorillas and Chimpanzees. This is significant - especially for those who believe extinct species may have survived. Great Apes are hardly invisible, so if one species can survive without science noticing, then so can others.
- Gigantopithecus blacki - Not a recent find, but a fascinating piece of the Great Ape history, being the largest ape that ever lived.
- Ardipithecus member, somewhere between A. ramidus and A. afarensis ("Lucy"). Until recently, the find called "Lucy" was the oldest known hominid that walked predominantly upright. What interested a lot of people was that "Lucy" was NOT a direct ancestor, showing that hominids have discovered walking multiple times in history.
- Early humanoid cultures? - hints of multiple pre-Neanderthal cultures in Britain, 500,000 years ago
- Pierolapithecus catalaunicus - a "missing link" between early primates and the Great Apes
- The Guardian was another news source that covered the discovery of Pierolapithecus catalaunicus
- Lufengpithecus chiangmuanensis - a "missing link" showing the oldest-known close relative of the Orang-Utang. This is probably what Pierolapithecus catalaunicus became, immediately prior to evolving into the Orang-Utang, which gives us a glimpse into how the Orang-Utang came into being.
- The science behind the study of Lufengpithecus chiangmuanensis. Spectroscopy and synchrotron radiation are fascinating tools and this is an interesting use of them
- Orang-Utangs have an amazingly sophisticated proto-culture, which indicates that early societies likely evolved before humans.
- Sahelanthropus tchadensis - the earliest hominid known, at 7 million years old. The evidence is increasingly strong that hominids followed a great many paths. What is not clear is which path or paths modern humans are related to, or even if the distant (but direct) ancestors of humans are even amongst the species identified. Because scientists rely on shape, and because shape can evolve multiple times, it is hard to tell if or how two similar shapes are related.
- Sahelanthropus tchadensis Homepage - now, if only they could travel back in time and set up a webcam...
- Talkorigins has an excellent page and some good links for Sahelanthropus tchadensis
- Homo floresiensis has been covered quite a bit, here and elsewhere, but if you're going to try for a complete picture, it would be stupid to miss this out
- The Guardian's Editorial/Blog gives a more satirical look at the discovery of Homo floresiensis (though it's modern humans who get the short end!)
The sum of the above seems to be as follows:
- The timespan for the evolution of humans from apes is much shorter than previously believed
- The diversity (and scale) of hominid species is much greater than previously thought
- The maximum number of Great Ape species alive at any one time peaked at about 100. The total number of Great Ape species is unknown but obviously much larger - this is based on known fossils, and estimating the age of a fossil by what it is around that we do know the age of. Since so few specimins fossilize, the peak number of species may get revised, although it seems fairly solid at this point
- No good candidate for a direct ancestor of humans can be found (although some candidates have been ruled out such as Neanderthals). The opinion seems to be that evolution around that time was "messy". Modern humans may be a blend of different hominids, but there just isn't enough hard data to know for certain. The problem is, without genetic data, it is hard to know how "close" or "distant" any fossil find is from homo sapien or its predecessors.
- What seems to be certain, though, is that the rate of change of a species is not fixed, but can vary quite wildly over relatively short timeframes. This suggests the environment impacts genetic material with all the subtlety of a sledge-hammer.
- With the discovery of the "hobbit-like" humans, there is renewed interest in the possibility that folklore is based on far, far older cultural memories, perhaps running tens of thousands of years into the past. This would require that societies capable of preserving such memories have to be equally old
- Creationists, as I expected, are getting increasingly upset with the fact that fossil finds are filling in the gaps well within the expected bounds, thus completing the "missing link" surprisingly well
- Indications of either multiple hominid species OR multiple cultures within Britain about 500,000 years ago is creating a stir, as the indirect evidence builds some amazing possibilities, but the direct evidence for any of them remains elusive
To me, these are fascinating. They not only fill in some irritating gaps in human knowledge, but they also serve to create puzzles and intrigues that might never be solved. How many hominid species were there? How many hominid migrations from Africa were there? How much mixing was possible between them?
Then, there are mysteries which may well be solved but not always to our liking. The "hobbit-like" humanoids MAY have existed up until a few centuries ago. There are clues which suggest that, but nothing definite. Other hominids, therefore, may also have survived, but we've even less evidence of those. But it is possible. The legends may actually be based on factual observations, at some point in history. (But as verbal history can survive thousands of years, that doesn't mean any exist today. Again, though, they might.)
Of course, I'm going to finish this with an evil thought. Let's say that an early hominid species DOES exist, perhaps in America. Would we recognize it as essentially human and grant it rights on that basis, or would we treat it as merely a large monkey and throw it in a zoo? At what point does life have to be "human enough" to get decent treatment?