A question for evolustionists

[Rev. Rye]

If evolution got us humans where we are today, why didn't all animals keep evolving until they're humans?

This question makes as much sense as "If all humans are related, why don't they all look like me?"

Also, why are humans the last stop on the evolutionary train?

No, we're not the last stop; merely the current one. Evolution does not claim that there is even supposed to be a final stop. Evolution does not have a specific goal, with the possible exception of "adapt to your surroundings." It's too soon to figure out what the next stop would be; but, with human ability to change the environment to suit its needs, it's unlikely that we'll change too drastically in the next few millennia.

Why haven't humans evolved into 10 armed 3 headed super-humans?

Let me explain how evolution works: It happens when a mutation occurs that turns out to be effective for use in one's environment, to the point where the mutants eventually thrive better than the non-mutants in the environment and, after several generations (a few dozen should suffice, but it could take longer), the mutants have effectively become a new species. So, simply put, since multiple heads and supernumerary limbs haven't yet proven themselves to have had an advantage (indeed, until relatively recently, "Siamese Twins" didn't live long after birth, and, only one person with three fully-formed arms has been recorded and he hasn't yet reached his fifth birthday), and since it's unlikely that two people with multiple heads or arms have ever bred (and even if there were two sets of conjoined twins that married each other, there is no record of a set of conjoined twins giving births or siring another set), the odds of them producing anything coming close to such "10 armed 3 headed super-humans" is very rare. For that matter, conjoined twins (the closest thing to multi-cephalic people you described) have a big problem getting around in the world and don't really have much of an advantage compared to most other "normal" people. Does this answer your question?