Theory of Evolution terms. What is this called?

I think the term you're looking for is 'transitional form'.

Some people who don't know much about evolution use the term 'missing link', but this is a bogus concept that misunderstands evolution completely.

As for why there are no half-ape/half-men ... this is because the *definition* of the word 'species' is that there is no cross-breeding.

To understand this, it's important to understand the concept of *BRANCHING* ... the way that new species are born.

A given species may get split into two sub-populations that are separated by some barrier (maybe a river cuts through a valley, or a valley between mountain ranges dries up, or a bad drought causes a long migration ... many reasons).

Once these two subpopulations are not interbreeding, they cannot exchange genetics. So changes in one population do not get transmitted (through breeding) to the other population. So the two populations over time get more and more different.

If enough time goes by (say a few hundred-thousand years), the two populations will lose the ability to cross-breed at all ... even if they come into contact. At that point, they are no longer the same 'species' ... they are separate species. This is called 'branching' (or more technically 'speciation' ... there are other ways that speciation can occur besides geographic isolation, but this is the simplest).

Once they are two species, they can never, ever become the same species again. So they will *continue* to get more and more different as the thousands of years stretch into millions.

So one species gets more and more like modern humans and the other species gets more and more like (say) modern chimpanzees.

For each species, as long as all its members can interbreed, so that genetic changes eventually spread throughout the species, the species will continue to change *as a whole*. It's not like some members can remain frozen in some early stage of evolution closer to the ancestor species, while others continue to evolve. So all the members of the same species continue to look like each other within a certain range.

And since humans and chimps cannot cross-breed, there cannot be any new half-chimp/half-man hybrids. It's just not genetically possible.

Hope that answers your question.

Transitional forms / fossils. As stated, everything is transitional, but there are a number of series between major groups.

Some who argue against it call that missing transitional forms. There is no such thing as a creature that is not transitional. All organism evolve so they are all transitional and they are all complete.

To the Additional Details:

People always say that man came from apes...well, I think its Darwin that says this (not 100% sure),but he says that we don't evolve from them, we came from the same ancestor as them.