QUESTION: I often read about the discoveries of fossils of the different species of early man, but have there been discoveries of fossils of "half apes" or discoveries of earlier steps in reaching these stages? Thanks, Bob Walshaw.
PS- I have been an Expert for many years - Bluebirds, birds, job tips.
ANSWER: Hi Bob,
DNA variation among living apes, humans suggests the last common ancestors of apes and humans lived around 6 million years ago. The fossil record for this time period is kind of sketchy, but it is getting much better recently. The lineage leading from the last common ancestor to us is richly populated by species of the genus Australopithecus (and new ones, Ardipithicus, and Sahelanthropus). There appears to have been a radiation in bipedal apes fairly soon after the split with last common ancestor, so there is a lot of controversy over which, if any, of the fossils between 6-2 Million years ago are ancestral to Homo sapiens.
The lineages leading to apes are not well-documented, probably because ancestral apes lived in habitats like forests, in which fossils do not form easily. One exception is Sivapithecus, from Pakistan, that is pretty clearly an ancestral orangutan.
If you are more interested in the evolution primates before humans, then John Fleagle's Primate Evolution and Adaptation is the best reference out there.
For an introduction-level book on human evolution Peter Andrews and Chris Stringer's Complete World of Human Evolution is a good start. The college-level text many of us use for teaching human evolution is Richard Klein's The Human Career (3rd Edition). It emphasizes more recent periods of human evolution.
---------- FOLLOW-UP ----------
QUESTION: Thanks. Well said. What I am curious about is the evolutionary path to the pre-humans or apes. Any indication in the Pakistan fossil? In animals like birds we have a path from some of the dinosaurs for example. Thanks, Bob Walshaw.
The origins of the apes lie in the Oligocene and Miocene Epochs. There are lots of fossils. These periods witnessed a huge diversification of ape species followed by a reduction in species diversity in more recent times (edged out by monkeys on the one side, hominins on the other).
This is not a subject on which I am an expert, but it is one on which my colleague, John Fleagle, is one. The newest edition (3rd?) of his book, Primate Adaptation and Evolution, is the best source of information about this.