A common misconception about evolution is that "lower" species evolve into "higher" species. This views evolution as a ladder with humans at the top. But that is not what evolution is.

In evolution there are no higher or lower species and evolution is a tree rather than a ladder. Evolution is a tree with branching limbs, each species evolving from common ancestor with related species.
An example is human ancestry, humans and chimpanzees share a common ancestor and that shares a common ancestor with gorillas.

Wikipedia - Common descent
Understanding Evolution - The family tree
Evolution 101 - Trees, Not Ladders

Part 4
Part 6
Evolution main page

Edit: This is not written well, I'll do a rewrite soon.