If you don't understand that, then you don't have a basis for rejecting evolution.
Think of it this way: new breeds of dog are developed all the time. Pit Bulls were developed from other terriers, yet there are still other terriers around. This is because the breeder took a few of the other terriers and bred from them. The other terriers continued to reproduce, and are still around. Or rather, their descendants are: they splintered into other breeds besides.
Likewise with humans: ONE particular group of monkeys developed in such a way as led to humans. All other groups of monkeys developed in different ways.
Please tell me you understand this very basic point now.