[tolbiny]

While not an expert i do have some background in this.

"If man evolved from apes, then why aren't there any half man-apes around in the process of becoming fully man?"

The simple answer to your first questionis that the half man half apes were out competed by humans. Around 200,000k yrs ago we find evidence of what are considered the first anatomically modern [censored] sapiens. At this time there exists a different species, [censored] neanderthalensis. There are also the last survivors of a species know as [censored] erectus. erectus is probably the "apeman" you are thinking off- he walked upright, had an average brain size of around 1000ccs (humas average around 1400, chimps around 450 iirc), made and used stone tools and controlled fire. His skeleton diffeered from H. sapiens in a couple of ways- 1 obviously he had a smally skull (smaller brain)- but it was shaped differently as well. It is longer than it is high (in humans its higher than it is long) and it is wider at the base of the cranium than it is at the top (in humans it is widest just above the ears) and erectus exhibits strongly prounounced double arched brow ridges (humans are unnoticible by comparison). There are also dental differences is the size of teeth, and no erectus specimin has been found exhibiting a chin. They are clearly a different species from sapiens. Otherwise they were very similar to anatomically modern [censored] sapiens (AMHS), shared the same diet and habitat. Once they eveolved AMHS outcompeted erectus. Where would you find such apemen? Anywhere they might have lived humans have moved into and driven them to extinction.

"Did the genus of ape we evolved from suddenly stop evolving into man?"

Apes and humans split from a common ancestor around 6 million years ago. Apes have evolved since then, our common ancestor probably looked as different from chimps as we look different from chimps. There were many steps between this common ancestor and us. Adaptations that allowed us to walk upright, carry things more efficiently, communicate, larger brains ect. A million years ago the hominids that walked around weren't human, they were a different species, different from what came before them, and different from what was to follow. We don't show up until around 200k years ago.

"Why do we find that one species is often so clearly defined from other species?"
I can never describe this one well- the easy answer is time. Stuff has been around long enough to specialize into a specific habitat.

"I have some problem with the so-called Cambrian explosion too"
Ask away, while i am not very strong in PE thoery, i can probably answer a question or two.