Subject: Logical Problem in evolution?

If I understand the way evolution works correctly, the first stage is a 
random mutation. Then, through the process of selection (survival of the 
fittest) the bad mutations are killed off and only the good mutations 
stay. But not all mutations are life or death - My question is why after 
so many years are we still so similar too our predecesors and why don't we 
have any really useless body parts. For example, if someone is born with 6 
fingers instead of 5, this doesn't kill him off, in fact it even helps 
him. Why dont we all have 6 fingers then? I hope you understood my 
question :-)

Re: Logical Problem in evolution?